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In many nuclear families, dependent offspring receive unequal shares of parental investment. Initial overproduction can be adaptive from the perspective of parents, but parents must be able to identify appropriate candidates for favourite status. We studied early nestling development in house sparrows (Passer domesticus), a species in which the loss of some brood members is common, testing the prediction that body mass and carotenoid-rich flange colours are important to nestling success. There was substantial variation in both traits within broods, even only 1 day after hatching. Nestlings low in the within-brood mass hierarchy gained more mass if they displayed more carotenoid-rich flanges than broodmates. Position in the colour hierarchy did not, however, predict mass gain for individuals that were heavier than their broodmates. Nestlings that were heavier or had more carotenoid-rich mouths were also less likely to be the victim of brood reduction. Our results suggest that house sparrow parents use both nestling body size and mouth colour when making allocation decisions. Understanding both how and when offspring traits and parental preferences function is key to understanding how selective pressures act on offspring–parent communication. [ABSTRACT FROM AUTHOR]

Altricial birds often display biased preferences in providing parental care for their dependent offspring, especially during food shortages. During this process, such inflexible rules may result in provisioning errors. To demonstrate how parents optimize their provisioning strategies, we proposed a "diagnosis model" of parental care to posit that parents will undergo a diagnosis procedure to test whether selecting against some particular offspring based on phenotype is an optimal strategy. We tested this model in an asynchronous hatching bird, the Azure-winged Magpie Cyanopica cyanus , based on 10 years of data about demography and parental provisioning behaviors. Given their higher daily survival rates, core offspring (those hatched on the first day) merits an investment priority compared with their marginal brood mates (those hatched on later days). However, a marginal offspring also merited a priority if it displayed greater weight gain than the expected value at the early post-hatching days. Parents could detect such a marginal offspring via a diagnosis strategy, in which they provisioned the brood at the diagnosis stage by delivering food to every nestling that begged, then biased food toward high-value nestlings at the subsequent decision stage by making a negative response to the begging of low-value nestlings. In this provisioning strategy, the growth performance of a nestling became a more reliable indicator of its investment value than its hatching order or competitive ability. Our findings provide evidence for this "diagnosis model of parental care" wherein parents use a diagnosis method to optimize their provisioning strategy in brood reduction. [ABSTRACT FROM AUTHOR]

Resource limitations, either due to environmental conditions or constraints on parental provisioning effort, can drive intense competition among offspring. In communal groups, resource availability may increase if parents receive assistance from other group members; however, if those caregivers also produce young, offspring demand may increase at the same time. It is possible, therefore, that the costs of intrabrood competition in large broods may outweigh the benefits of provisioning from additional caregivers. We tested the relationships between group size, brood size, and provisioning rates in the greater ani (Crotophaga major), a communally nesting cuckoo in which multiple breeding pairs and nonreproductive helpers cooperatively raise a shared brood. Crucially, brood and group size can vary independently in this species, allowing us to test changes in each variable separately. Using video footage of 2255 prey deliveries across 10 nests, we found that an increase in the number of adult caregivers within a group did not sufficiently offset a corresponding increase in the number of dependent young within a brood: prey availability per average nestling decreased with brood size, regardless of group size. In larger broods, last-hatched nestlings received significantly less prey than their broodmates, in part due to greater hatching asynchrony that exacerbated competitive asymmetries and facilitated inequality in food allocation. Our results indicate that last-hatched ani nestlings suffer a "double cost" in large broods: they must compete with more nestmates, and suffer disproportionately from asynchronous hatching. These costs may contribute to increased parent–offspring conflict and may constrain group size in communal breeders. [ABSTRACT FROM AUTHOR]

Simple Summary: In some species of birds, asynchronous hatching occurs when incubation begins before completion of clutch, resulting in age differences between nestlings. According to the brood reduction hypothesis, which explains the reason for asynchronous hatching, selective survival is permitted only for older nestlings when availability of food is unpredictable. Due to the feature of food distribution, passerines are not likely to practice selective feeding of older nestlings. The essential purpose of this study is to determine whether the brood reduction hypothesis can explain asynchronous hatching in passerines. Infrared cameras were installed inside nest boxes to determine whether great tit (Parus major) parents, which show asynchronous hatching, practices selective feeding of older nestlings. The results of this study showed that great tit parents did not practice selective feeding of older nestlings, highlighting that using the brood reduction hypothesis to explain asynchronous hatching of great tits is not reasonable. Further research is needed in order to explain the adaptiveness of asynchronous hatching. The brood reduction hypothesis, which explains asynchronous hatching in birds, as an adaptation that enables selective survival of older nestlings when availability of food is unpredictable. This study was conducted in order to determine whether the brood reduction hypothesis can explain asynchronous hatching in passerines. Infrared cameras were installed inside nest boxes where great tits (Parus major) were attempting to reproduce in order to determine whether the parents practiced selective feeding of older nestlings. According to the results of the study, no significant difference was observed between the hatching order and the average number of feedings per nestling. In addition, when examining the distribution of food according to hatching order over time, every 30 min, beginning at 9 a.m., selective distribution of food to older nestlings was not observed. In conclusion, use of the brood reduction hypothesis, which supports selective provision of beneficial feeding of older and larger nestlings, to explain the asynchronous hatching of passerines is problematic, thus conduct of future studies focusing on other hypotheses in order to explain the asynchronous hatching of this passerine bird will be necessary. [ABSTRACT FROM AUTHOR]

I examined sex allocation of offspring in northern flickers, Colaptes auratus , a woodpecker with biparental care and sexual size dimorphism. The analysis of data involving 8321 nestlings that were sexed over a span of 16 years revealed no significant bias towards the smaller sex (females) at the population level (all fledglings pooled), counter to the Fisherian hypothesis of equal investment at the end of parental care. At the level of the brood, high-quality parents (older and in better body condition) did not produce more of the expensive sex (males) counter to the Trivers–Willard hypothesis. Brood sex ratios were somewhat repeatable among females but did not vary significantly with year, clutch size or hatching date probably because the main food of flickers, ground-dwelling ants, is relatively invariable. Mother flickers allocated more of the cheaper sex to last-hatched offspring in asynchronous broods, consistent with the 'intrabrood sharing-out hypothesis' but not the 'competitive advantage hypothesis'. The female-bias in last-laid eggs was present in complete broods, which had no nestling mortality, suggesting that primary sex ratio manipulation was involved. However, a small shift in the direction of female-bias occurred as a result of a greater mortality of the more costly (male) nestlings. Female flickers may therefore attempt to minimize maladaptive brood reduction by allocating more of the cheaper sex to positions later in the laying sequence. • Population level offspring sex ratio of northern flickers did not differ from parity. • High-quality parents did not produce more males (the expensive sex). • Flickers allocated more females to last-hatched offspring within asynchronous broods. • Female bias in last-laid eggs was present in broods without nestling mortality. • Sex allocation was consistent with the 'intrabrood sharing-out hypothesis'. [ABSTRACT FROM AUTHOR]

Sex allocation theory predicts that species with reversed sexual size dimorphism frequently overproduce the cheapest sex at the brood level. A sex ratio deviation from parity is frequently documented among the offspring of raptors and is largely produced by sex-biased survival or parental adjustment as a response to environmental variability or demographic conditions. The Eleonora's falcon is a long-distance migrant wintering in Madagascar and southeast Africa and breeding colonially primarily in the Mediterranean Sea and the Canary Islands. It feeds on migratory passerines and thus depends greatly on the autumn migration flow and the prevailing winds. Being sexually size dimorphic (i.e. females are larger than males) and depending greatly on the migration, the species is a good case for investigating whether brood sex ratio variation is adaptive. In the present study, we examined the proportion of males and females reared during 2009–2020 in a falcon colony in southeast Crete (Greece) in relation to specific ecological and biological attributes. Female nestlings were shown to be costlier to produce as they are heavier than males. Overall, an unbiased sex ratio was observed across the years, although a consistent trend was recorded towards females early in the breeding season and first-hatched chicks and males late in the breeding season and third-hatched chicks. Our results provide strong evidence that parental condition, habitat quality and a brood reduction effect were the significant drivers for the observed sex ratio patterns. The overproduction of the costlier sex and a high survival of the cheaper one during food-rich years should be regarded as an adaptive evolutionary strategy of the species for maximizing its fitness returns per clutch and for maintaining a balanced offspring sex ratio in the population. • The overall sex ratio in 2009–2020 was 1:1. • The sex ratio was biased towards females in early and first-hatched chicks. • The sex ratio was biased towards males in late and third-hatched chicks. • Parental condition and habitat quality are significant drivers for sex ratio. • Sex ratio adjustment is an adaptive evolutionary strategy. [ABSTRACT FROM AUTHOR]

Brood reduction is a frequent outcome in asynchronously hatching birds. In these species, first-hatched nestlings get a disproportionately larger share of the food delivered by parents, often leading the youngest nestling to starve to death soon after hatching. However, we still do not know the proximate mechanisms of such brood reduction. Starvation of the smallest nestling may be the outcome of scramble competition among nestmates (due to brood size hierarchies) or, alternatively, be caused by parents that ignore the persistent begging from their smallest nestling. To determine whether parents or scramble competition among siblings induces brood reduction, we used a cross-fostering approach to experimentally create asynchronous Eurasian blackbird, Turdus merula , broods. Then, we assessed food allocation by parents in two different situations: when sibling competition was allowed and when competition was prevented by physically separating nestlings with wooden barriers placed within the nest. We found that smaller nestlings experimentally introduced into blackbird nests received less food than their larger nestmates regardless of whether scramble competition among nestlings was allowed or not. Males preferentially fed larger nestlings regardless of the competitive context, while females showed no feeding differences. Our results suggest that nestlings may exert limited control over parental food allocation. • The smallest nestling usually starves in asynchronously hatched broods. • This can be due to nestling control, parental control or both. • Smaller nestlings received less food regardless of the competitive situation. • Parents actively ignore the smallest nestling. [ABSTRACT FROM AUTHOR]

Generalist brood parasites that share nests with host nestlings can optimize resource acquisition from host parents by balancing the benefits that host nest-mates provide, including attracting increased provisions to the nest, against the costs of competing with the same host young over foster parental resources. However, it is unclear how parasitic chicks cope when faced with more nest-mates than are optimal for their survival upon hatching. We suggest that, in the obligate brood parasitic brown-headed cowbird (Molothrus ater), chicks use a niche construction strategy and reduce larger, more competitive host broods to maximize the parasites' survival to fledging. We experimentally altered brood sizes to test for Goldilocks principle patterns (i.e. a 'just right' intermediate brood size) of cowbird survival in nests of prothonotary warbler (Protonotaria citrea) hosts. We found that intermediate brood sizes of two host nestlings maximized cowbird fledging success relative to 0 or 4 host nest-mates at hatching. Specifically, cowbird nestlings lowered host brood sizes towards this optimum when placed in broods with more host nestlings. The results suggest that cowbirds reduce, but do not eliminate, host broods as a niche construction mechanism to improve their own probability of survival. [ABSTRACT FROM AUTHOR]

Post-natal growth has long-term consequences for survival and fitness in birds and is subject to strong directional selection. Highly variable patterns of nestling development are influenced by an array of extrinsic and intrinsic factors. This study analysed the impacts of hatching order, nestling subperiod, brood size and weather conditions, all of which could influence the growth rate of Marsh Harrier Circus aeruginosus nestlings. It was conducted over a period of 6 years, during which measurements of 173 nestlings from 66 nests were made at fishpond complexes in eastern Poland. Relative growth rates (RGR) were calculated on the basis of tarsus and wing lengths during two subperiods of nestling development. Linear mixed models showed that the hatching order and nestling subperiod influenced nestling growth, whereas brood size did not affect wing or tarsus relative growth rates. The effect of hatching order differed between the two traits and between subperiods. Marginal nestlings in broods of five exhibited poor wing growth and perished before fledging. In contrast to wing growth, tarsus growth rates were similar in all the siblings in the first subperiod. During the second developmental subperiod, the growth rates of both locomotor traits exhibited the same pattern, i.e., higher values in the later-hatched chicks than in the earlier ones. Precipitation, but not temperature, had a negative impact on growth in the second subperiod. Our results show a variation in growth patterns between nestmates, which was the most evident in the rate of wing growth. The study enhances our understanding of brood reduction and cainism in birds of prey. [ABSTRACT FROM AUTHOR]

The article explores Fisheries managers used the fish toxicant rotenone to eradicate an undesirable brown bullhead (Ameiurus nebulosus) population and all other fish species at Hyatt Reservoir, Oregon, on 12 October 1989. This 4-yr study (1988–1990, 1992) compared effects of that rotenone project on Ospreys (Pandion haliaetus) nesting at Hyatt Reservoir.

The article presents the discussion on sibling aggression leading to siblicide documented in a wide variety of bird species. Topics include facultative siblicide resulting from competition for limited food resources; and showing asynchronous hatching, altricial development, sexual size dimorphism, spatial and temporal concentration of food, and small brood size.

Filial cannibalism (cannibalistic infanticide) is a common strategy among raptors though rare among other groups of birds. We describe the first case of possible parental infanticide followed by cannibalism by an adult and nestmates of Red-legged Seriema (Cariama cristata) in a brood of 3 in the Cerrado (savanna-like) ecosystem. A 20 min video recording showed a possible parent killing and eviscerating 1 of its nestlings and subsequently feeding it to the other 2 nestmates. This new record of brood reduction for wild Cariamidae might be a common behavior in both species of the family and may increase food availability and survival of the larger nestlings. [ABSTRACT FROM AUTHOR]

The effect of asynchronous hatching on nestling health and condition in ardeids is still in need of empirical evidence from populations living in different environmental conditions. Using morphometric and hematologic data from Little Egret Egretta garzetta nestlings in a Tunisian breeding colony, we assessed the relationship between hatching order and nestling condition, while accounting for the effects of brood size, age and hatching date. Our results showed that the youngest nestlings had lower values of hematocrit and body condition index but higher levels of fluctuating asymmetry compared with their older siblings. These trends seem to stem from increased nutritional stress experienced by younger nestlings who would have received less food from their parents than their siblings due to their less competitive nature. Additional constraints during the rearing period, such as possible injuries resulting from conflicts with siblings and the energy cost of thermoregulation, may also have contributed to the deterioration of the condition of last nestlings. Overall, our findings provide empirical evidence of the short-term repercussions of asynchronous hatching in a North African population of Little Egrets. They also highlight the great complexity of mechanisms by which asynchronous hatching may affect body condition and health of bird nestlings. [ABSTRACT FROM AUTHOR]

In animals with uniparental care, the quality of care provided by one sex can deeply impact the reproductive success of both sexes. Studying variation in parental care quality within a species and which factors may affect it can, therefore, shed important light on patterns of mate choice and other reproductive decisions observed in nature. Using Syngnathus typhle , a pipefish species with extensive uniparental male care, with embryos developing inside a brood pouch during a lengthy pregnancy, we assessed how egg size (which correlates positively with female size), male size, and water temperature affect brooding traits that relate to male care quality, all measured on day 18, approximately 1/3, of the brooding period. We found that larger males brooded eggs at lower densities, and their embryos were heavier than those of small males independent of initial egg size. However, large males had lower embryo survival relative to small males. We found no effect of egg size or of paternal size on within-pouch oxygen levels, but oxygen levels were significantly higher in the bottom than the middle section of the pouch. Males that brooded at higher temperatures had lower pouch oxygen levels presumably because of higher embryo developmental rates, as more developed embryos consume more oxygen. Together, our results suggest that small and large males follow distinct paternal strategies: large males positively affect embryo size whereas small males favor embryo survival. As females prefer large mates, offspring size at independence may be more important to female fitness than offspring survival during development. [ABSTRACT FROM AUTHOR]

Selective elimination of excess offspring with poor fitness prospects may occur prenatally (selective abortion) or postnatally (brood reduction). Postnatal reduction is the dominant strategy, presumably because surplus progeny serves as a hedge against environmental and developmental uncertainty. In birds, its main proximate mechanism is asynchronous hatching, generating within-brood competitive asymmetry. Here, clutch-size reduction via last-egg abandonment was investigated in the asynchronous [ABSTRACT FROM AUTHOR]

Earlier offspring mortality before independence saves resources for kin, which should be more beneficial when food is short. Using 24 years of data on age-specific common tern (Sterna hirundo) chick mortality, best described by the Gompertz function, and estimates of energy consumption per age of mortality, we investigated how energy wasted on nonfledged chicks depends on brood size, hatching order, and annual abundance of herring (Clupea harengus), the main food source. We found mortality directly after hatching (Gompertz baseline mortality) to be high and to increase with decreasing herring abundance. Mortality declined with age at a rate relatively insensitive to herring abundance. The sensitivity of baseline mortality to herring abundance reduced energy wasted on nonfledged chicks when herring was in short supply. Among chicks that did not fledge, last-hatched chicks were less costly than earlier-hatched chicks because of their earlier mortality. However, per hatchling produced, the least energy was wasted on chicks without siblings because their baseline mortality was most sensitive to herring abundance. We suggest that earlier mortality of offspring when food is short facilitates economic adjustment of posthatching parental investment to food abundance but that such economic brood reduction may be constrained by sibling competition. [ABSTRACT FROM AUTHOR]

In a food-limited system, parents may have to allocate resources in ways that do not benefit all their offspring equally. We investigated food allocation and parent and chick behaviours in Magellanic penguins at their colony in Punta Tombo, Argentina, by observing feedings in one- and two-chick broods after the chicks were more than 20 days of age. Feeds lasted 21 min on average, and the length of a feed was not correlated either with the number of chicks in a brood, or with the amount of food the parents gave. Parents with two-chick broods distributed food evenly to both chicks. Although single chicks were fed more than chicks with siblings, as a proportion of a chick's start weight, both single chicks and lighter chicks in two-chick broods received significantly more food than heavier chicks. Chicks continued begging after the last feed in nearly half of the two-chick broods, suggesting they were not sated and so are food-limited. In linear mixed-effects models that considered, respectively, the absolute amount of food a chick received and the amount of food it received as a proportion of its start weight, chick begging was the most significant predictor of how much it was fed. Jostling behaviours between the chicks did not correlate with the amount of food either one received. Parental nonfeeding behaviours in two-chick broods (e.g. bending towards a chick and opening the bill but not regurgitating food) were more frequently directed at the lighter chick, but did not correlate with the amount of food a chick received. These results suggest (1) parents are motived to feed their chicks quickly, (2) parents try to allocate food equally to chicks of this age and (3) chicks devote most of their energy trying to get fed by the parent, rather than competing antagonistically with one another. Highlights • We observed parental and chick behaviour of Magellanic penguins during feeds. • Parents distributed food equally between heavier and lighter chicks >20 days old. • As a proportion of a chick's start weight, lighter chicks received more food. • A chick's begging was the most significant predictor of how much it was fed. • Chicks begged energetically for food but did not generally antagonize each other. [ABSTRACT FROM AUTHOR]

Brood reduction by parents via infanticide is considered rare in passerine birds; however, this behavior may be underreported because of the difficulties observing behaviors at the nest and because researchers tend to attribute partial nestling loss to other causes. Here, we report a confirmed incidence of parental infanticide by Dickcissels (Spiza americana). While video-recording parental behavior, we documented a 4-day-old nestling being removed by a female Dickcissel. This bird was also observed brooding and feeding, so this event was likely a parental infanticide. We subsequently examined monitoring data from 162 hatched Dickcissel nests across 2 breeding seasons to identify instances of unexplained partial nestling loss, which could potentially be attributable to infanticide. Our data indicate that 9.1-12.7% of hatched nests experienced these events. Infanticide by genetic parents could (1) benefit survival of remaining brood mates by reducing food requirements, disease, or predation risk; (2) represent responses to cuckoldry or intraspecific brood parasitism; (3) represent cases of mistaken chick identity; or (4) be triggered by unusual stressors. We recommend that ecologists monitoring bird nests consider infanticide as a possible explanation for partial nestling loss. [ABSTRACT FROM AUTHOR]

Brood reduction by parents via infanticide is considered rare in passerine birds; however, this behavior may be underreported because of the difficulties observing behaviors at the nest and because researchers tend to attribute partial nestling loss to other causes. Here, we report a confirmed incidence of parental infanticide by Dickcissels ( Spiza americana). While video-recording parental behavior, we documented a 4-day-old nestling being removed by a female Dickcissel. This bird was also observed brooding and feeding, so this event was likely a parental infanticide. We subsequently examined monitoring data from 162 hatched Dickcissel nests across 2 breeding seasons to identify instances of unexplained partial nestling loss, which could potentially be attributable to infanticide. Our data indicate that 9.1-12.7% of hatched nests experienced these events. Infanticide by genetic parents could (1) benefit survival of remaining brood mates by reducing food requirements, disease, or predation risk; (2) represent responses to cuckoldry or intraspecific brood parasitism; (3) represent cases of mistaken chick identity; or (4) be triggered by unusual stressors. We recommend that ecologists monitoring bird nests consider infanticide as a possible explanation for partial nestling loss. Received 3 November 2016. Accepted 27 November 2017. [ABSTRACT FROM AUTHOR]

The article focuses on the asynchronous hatching in birds. It includes information on the siblicide, parental infanticide, and cannibalism in the nest of Northern Goshawks. It also discusses topics including brood reduction, impact of nesting season on the brood size, and setup of video recording system by the author for bird observation.

Hatching asynchrony occurs primarily as a consequence of the timing of embryonic development. Despite over 50 years of study, it is unclear why, ultimately, most birds initiate embryonic development (incubation) before all eggs are laid. One hypothesis focuses on prehatching (embryo) survival and predicts that early incubation maximizes embryo survival by reducing exposure of unincubated eggs (egg viability hypothesis). Another set of hypotheses focuses on posthatching growth and survival and predicts that females time incubation to maximize the number or quality of hatched offspring that fledge (adaptive hatching pattern hypotheses). I experimentally manipulated when females could begin incubation to test how timing of embryonic development influences prehatching survival and posthatching growth and survival in the house sparrow, Passer domesticus . Despite high embryo survival in both naturally asynchronous and experimentally synchronized nests, early incubation appeared to maximize embryo survival in all but the earliest-laid eggs, suggesting that house sparrows begin incubation too late to maximize survival of all embryos. Early incubation had little effect on overall (i.e. mean) patterns of posthatching growth and survival. However, early incubation increased the initial variation in offspring size because last-hatched young were relatively small when all eggs had completed hatching. Nestlings that were small at hatch completion grew slowly and exhibited a reduced probability of survival, suggesting that house sparrows begin incubation too early to maximize growth and survival of hatched offspring. These results suggest that timing of incubation neither maximizes embryo survival nor maximizes posthatching growth and survival. Instead, early incubation appears to be a trade-off between maintaining both embryo survival and growth and survival of late-hatched offspring. Thus, house sparrow females likely time incubation as an adaptive strategy to maximize the number of embryos that survive the incubation and nestling periods to fledge. [ABSTRACT FROM AUTHOR]

Artificial selection of the domestic pig ( Sus scrofa domesticus ) offers a useful model for investigating changes in behaviour associated with reproductive trade-offs between litter size and fitness of offspring. The aim of this study was to evaluate effects of litter size on teat stimulation, sibling competition, and pre-weaning survival and growth in three populations of domestic pigs subjected to different selection pressures (a maternal line selected for high reproductive investment, a paternal line selected for meat production traits, and a crossbred line). We predicted that, with increasing litter size, piglets would spend more time in udder massage, be less likely to gain access to a teat during milk letdown and, if surviving to weaning, have lower, more variable body weights. We also predicted that maternal line sows would wean more piglets of higher weight, despite larger litter sizes, than paternal line sows. Sows (maternal line, n = 12, paternal line, n = 12, crossbred line, n = 14) were loose-housed with their litters in individual farrowing pens. We collected data on piglet behaviour during nursings at 1 day of age, when sibling competition was expected to be most intense. Piglets were weaned at 35 days of age, when they were weighed and cumulative mortality was calculated. As predicted, piglets in larger litters spent more time in pre- and post-letdown udder massage ( P = 0.050 and P < 0.001, respectively). In larger litters, more piglets survived to weaning ( P = 0.002), but at a cost of a lower proportion of nursings with letdown ( P < 0.001), longer nursing intervals on average ( P = 0.018), more piglets without a functional teat at letdown ( P < 0.001), an increased risk of mortality due to starvation ( P < 0.001) and crushing ( P = 0.002), and lower ( P = 0.039), more variable ( P = 0.002) body weights at weaning. In the maternal line, nursing intervals lengthened with increasing litter size (litter size × breed: P < 0.001) despite more post-letdown udder massage ( P < 0.001), and mortality due to crushing rose with increasing litter size ( P < 0.001), without differential increments in number, weight or weight uniformity of weaned piglets with increasing litter size between breeds (litter size × breed: P > 0.1). Our results suggest that further artificial selection for larger litters in maternal lines will be unsustainable because increments in the number of piglets weaned have increasing costs (e.g. sibling competition, mortality, uneven growth) that compromise piglet welfare and fitness. [ABSTRACT FROM AUTHOR]

A parent's nutritional state may influence its ability to provide care to offspring and ability to handle infections. In the broad-nosed pipefish, Syngnathus typhle, males care for their offspring by brooding the developing embryos in a brood pouch, providing nutrients and oxygen, resembling a pregnancy. Here, we demonstrate that the nutritional state of pregnant males covaries with their own survival during a selective event. Brooding males surviving a Vibrio sp. infection were in a significantly better nutritional state, as estimated by their hepatosomatic index. Furthermore, a higher nutritional state of the brooding male correlated with a lower embryo mortality, while feeding treatment (low vs. high) had no effect on male survival, nutritional state or embryo mortality. Finally, males brooding heavier embryos also showed a lower embryo mortality. This may reflect a maternal effect (if large eggs result in higher embryo survival), a paternal effect (if higher provisioning of male care promotes both embryo growth and survival), or a combination thereof (males caring more for large embryos). The results demonstrate the importance of a good nutritional state for a caring parent when their immunity is challenged. [ABSTRACT FROM AUTHOR]

Offspring are often produced in excess as insurance against stochastic events or unpredictable resources. This strategy may result in high early-life mortality, yet age-specific mortality before offspring independence and its associated costs have rarely been quantified. In this study, we modelled age-specific survival from hatching to fledging using 24 years of data on hatching order (HO), growth and age of mortality of more than 15 000 common tern (Sterna hirundo) chicks. We found that mortality peaked directly after hatching, after which it declined rapidly. Mortality hazard was best described with the Gompertz function, and was higher with later HO, mainly due to differences in baseline mortality hazard, rather than age-dependent mortality. Based on allometric mass-metabolism relationships and detailed growth curves of starving chicks, we estimated that the average metabolizable energy intake of non-fledged chicks was only 8.7% of the metabolizable energy intake of successful chicks during the nestling phase. Although 54% of hatchlings did not fledge, our estimates suggest them to have consumed only 9.3% of the total energy consumption of all hatched chicks in the population before fledging. We suggest that rapid mortality of excess offspring is part of an adaptive brood reduction strategy to the benefit of the parents. [ABSTRACT FROM AUTHOR]

Decision-making during different life-history stages requires information, which is obtained through own or others' experience and interaction with the environment. In birds, song is important for territory defense and mate attraction. Although song has evolved to purposely convey information, it can be inadvertently exploited by conspecifics. Experiments attempting to attract focal species by playing back their song are numerous, yet the consequences for reproductive performance remain little understood. In 2013 and 2014, settlement, reproduction, and extrapair paternity of Phylloscopus sibilatrix were assessed in a randomized experiment. We hypothesized that territory number, reproductive performance, and extrapair paternity would be higher on song plots (wood warbler song playbacks during prebreeding periods) than on control plots (no wood warbler song playback). On song plots, 3 times more territories were established, settlement occurred faster, and maximum plot occupancy was higher compared with control plots. Pairing rate, daily nest survival rate, mean clutch size, mean number of nestlings and fledglings, rates of extrapair young, nest abandonment, and nest predation did not differ between treatments, but fledging success was lower on song plots compared with control plots. This study shows the important role social cues can play for territory selection of birds, but also exemplifies the necessity for postattraction evaluation of reproduction to rule out negative effects of artificial attraction. Decreased fledging success on song plots and ambiguity about consequences of artificial attraction for distribution and settling dynamics of the species give reason to further evaluate whether acoustic attraction represents a suitable method for songbird conservation. [ABSTRACT FROM AUTHOR]

Hatching asynchrony is common among bird species. It results from starting incubation before clutch completion and is often accompanied by brood reduction, an adaptive strategy of the parents to selectively starve the younger chicks in times of food scarcity. The different developmental stages of nestlings are expected to affect their competitive abilities, their hunger state and thereby parental food allocation patterns. Here we used the combination of a correlative and an experimental field study to investigate sex-specific feeding patterns in the hoopoe, Upupa epops , in relation to a chick's rank and hunger state. Male parents showed a strong bias in their feeding pattern towards larger chicks, while females' feeding pattern was significantly more even. Only females were responsive to experimentally altered chicks' hunger state, especially so with small chicks at the lower end of the size hierarchy. This differential food allocation pattern mainly resulted from females mostly entering the nestbox to feed the chicks, while males more often delivered prey from the nestbox entrance hole without entering the cavity. Hence, when entering the nestbox, females can exert some parental control over food allocation, whereas competition among chicks to access the entrance hole mainly rules food allocation when the parents feed from the nestbox entrance hole. Similar sex-specific feeding patterns might be widespread in cavity breeders and it remains to be investigated to what extent variation in these male and female feeding patterns can affect nestling mortality and ultimately breeding success. [ABSTRACT FROM AUTHOR]

Maternal effects occur when the mother's phenotype influences her offspring's phenotype. In birds, differential allocation in egg yolk components can allow mothers to compensate for the competitive disadvantage of junior chicks. We hypothesize that the parent-older chick conflict peaks at intermediate conditions: parents benefit from the younger chick(s) survival, but its death benefits the older chick in terms of growth and survival. We thus expect maternal compensation to follow a bell-shaped pattern in relation to environmental conditions. We studied a black-legged kittiwake ( Rissa tridactyla) population where previous results revealed increased allocation of yolk testosterone in younger as compared to older chicks in intermediate conditions, in line with our theoretical framework. We therefore predicted a maternally induced increase in aggressiveness, growth, and survival for younger chicks born in intermediate environmental conditions. Controlling for parental effects and chick sex, we manipulated food availability before egg laying to create a situation with intermediate (Unfed group) and good (Fed group) environmental conditions. Within each feeding treatment, we further created experimental broods where the natural hatching order was reversed to maximize our chances to observe an effect of feeding treatment on the younger chicks' aggressiveness. As predicted, we found that chick aggressiveness was higher in younger chicks born from the Unfed group (i.e., in intermediate environmental conditions), but only when they were put in a senior position, in reversed broods. Predictions on growth and survival were not confirmed. Mothers thus seem to favor the competitiveness of their younger chick in intermediate conditions via egg yolk components, but our study also suggests that hatching asynchrony need to be small for maternal compensation to be efficient. We emphasize the need for further studies investigating other chick behaviors (e.g., begging) and focusing on the relative role of different yolk components in shaping parent-offspring conflict over sibling competition. [ABSTRACT FROM AUTHOR]

Sibling rivalry and brood reduction are traditionally considered to derive from food shortage. The aim of this study was to check this in the case of the Arabian babbler (Turdoides squamiceps) and to enhance our understanding of the negative and positive effects of each nestling on its siblings. We carried out 2 experiments: 1) we added for 1 day a foreign nestling to 18 nests in which a nestling had died on the previous day and 2) we removed from the nest for 2 h each individual from 10 four-nestling nests. We found that parents adequately adjusted their feeding rate to the introduction of a foreign nestling and that nestlings received less feeds when the removed nestling was smaller than them and more feeds when the removed nestling was larger than them. This finding corroborates Forbes's (2007) hypothesis by which smaller, hungrier nestlings are effective in soliciting additional feeds, many of which are eventually appropriated by the larger nestlings when brought to the nest. Nevertheless, a game-theoretic analysis shows that if the 4 nestlings are close in size, in terms of net energy gains, the larger nestlings actually lose from the presence of their youngest sibling, due to the increased evolutionarily stable strategy level of aggression in the nest; only if the youngest nestling is sufficiently smaller than them, aggression gets sufficiently diminished so that these additional feeds translate into net energy gains. A medium extent of clutch asymmetry, preventing excessive aggression while sustaining the smallest chick, may thus be beneficial to all. [ABSTRACT FROM AUTHOR]

Aerial insectivorous birds depend highly on favourable weather conditions for successful foraging because flight activity of insects is constrained by daily weather. Thus, the variation in weather conditions during reproduction, mediated by prey limitations, should be mirrored in annual reproduction performance, and finally in annual breeding success. We analysed the effect of local weather conditions on the availability of airborne insects and on the variation in brood size and nestling condition of European bee-eaters Merops apiaster at the northern edge of their range where years with adverse weather frequently occur. The availability of large flying insects, the common prey of bee-eaters, increased with air temperatures and duration of daily sunshine. As predicted, local weather conditions affected reproductive performance with annual breeding success (mean 3.7 nestlings per breeding pair, range 1.7-4.9 nestlings) being up to 32 % higher in extraordinary dry and hot summers. Additionally, a nestling's body condition (residual mass) was also affected by sunshine duration during their growth period and internally was co-affected by the number of siblings and the individual rank within the sibling hierarchy. Thus, a prolonged duration of daily sunshine causes a cascade from higher insect flight activity, and, thus, higher food availability for chick-rearing bee-eaters, which finally translates into better chick body conditions and higher annual breeding success. Consequently reproduction and population development of European bee-eaters might be especially susceptible to regional changes in weather and climatic conditions. [ABSTRACT FROM AUTHOR]

The asynchronous laying and hatching is one of the main aspects of the reproductive strategy of Ardeidae family and many hypotheses have been formulated to explain this phenomenon. In this paper I evaluate the morphometric differences between siblings at hatch and during growth, with data obtained in the Birama swamp, Cuba, for Nycticorax nycticorax, Bubulcus ibis, Ardea alba, Butorides virescens, Egretta tricolor, Egretta rufescens and Egretta thula. From 582 daily monitored nests I measured bill length, tarsus and body weight of siblings of known age. With these data, daily proportional difference between siblings was calculated for each variable and the trend of these differences during growth was analyzed. The differences between siblings at hatch were not significant in magnitude, been the highest percentual difference between first and third nestling detected in B. ibis. The species with greater intra-nest differentiation were N. nycticorax and E. rufescens, and species with more similar siblings was Ardea alba and the group of medium-sized herons and egrets. The trends of siblings asymmetries during the growth was different between species, and in four cases it was not associated with age. Ardea alba showed a definite decrease in hierarchy among siblings in all its variables, ranging from 6% to 2% during the first 14 days. In N. nycticorax relative differences between siblings increased significantly during growth (differences in peak range from 13 % at hatch to 68 % at 14 days of age). These results support that intra-nest hierarchy of sizes in nestlings depends more on hatching asynchrony and growth patterns, than on eggs size variation. [ABSTRACT FROM AUTHOR]

Parental phenotype and environment have cascading effects on offspring performance. Such 'maternal' effects are often mediated by the size and quality of the eggs in terms of maternal endogenous substances or exogenous components., Maternal effects can function to maximize parental fitness via adaptive allocation of components among sibling eggs. In birds, the often documented variation in concentration of egg dietary antioxidants or other egg compounds with laying order may thus reflect adaptive parental favouritism or maternal physiological constraints., Vitamins are found in the yolk at high concentrations and accomplish important physiological functions. Tocopherols ('vitamin E') have major roles in antioxidant protection, but the consequence of variation in their concentration for chick phenotype has never been experimentally investigated under a natural selection regime., In the yellow-legged gull ( Larus michahellis) free-ranging population we studied, vitamin E concentration and egg size decline from the first to the third (last) egg. Chicks from third eggs are smaller and have lower viability compared to those from sibling eggs. Here, we tested the effect of injecting a physiological dose of vitamin E in the egg yolk on chick body size at hatching by comparison with chicks from sham-injected eggs., As predicted, chicks from vitamin E injected third eggs were larger than chicks from control third eggs, whereas vitamin E had no effect on chicks from the other eggs. Thus, vitamin E injection disrupted the brood size hierarchy according to laying order normally found in this species., In species that adopt a brood reduction strategy, differential allocation of vitamin E to the eggs can contribute to establish a hierarchy of reproductive value among progeny members functioning to maximize parental fitness. The present results therefore have general implications for the study of the evolution of maternal effects mediated by transfer of potentially limiting maternal antioxidants to the eggs. [ABSTRACT FROM AUTHOR]

Siblicide may be “facultative” or “obligate”. When food resources provided by the parents are insufficient to rear a whole litter successfully, dominants may kill their subordinate siblings, either directly by physical damage, or indirectly through enforced starvation. This phenomenon is termed “facultative siblicide” and occurs in a wide range of bird species and at least one mammalian species. In contrast, when the lowest ranking sibling is routinely killed by its dominant brood mate or littermate this is called “obligate siblicide”, and seems to affect in particular large, long-lived species characterized by intense competition for breeding sites. This “obligate siblicide” has intrigued researchers for decades, trying to find an evolutionarily satisfactory explanation for this extreme behaviour. We review all scientific literature concerning sibling aggression published in the last 66 years. A bibliography search resulted in 104 references during the last 66 years, where birds represented 88% of the total published papers. Eleven hypotheses have been formulated for explaining these results, finding that siblicide is a complicated behaviour not controlled only for parents or chicks or environmental changes, but for a whole range of factors. These hypotheses have been identified and discussed according to actual supporting data. The relationship between food resources and brood reduction was widely documented; a sustained increase in food availability led to a highly significant decrease in both frequency and intensity of aggressiveness of the older chick towards its younger sibling in facultative species, also finding similar results in obligate siblicidal species. These results would suggest siblicide is an adaptive behaviour. This review tends to show that there is probably more than a single cause behind this behaviour. We conclude that more aspects must be considered in the design of future studies in order to understand the potential evolutionary sense of aggressive behaviour among siblings, especially those concerning food allocation decisions by parents. [ABSTRACT FROM PUBLISHER]

Intraclutch egg size variation in birds depends on many ecological factors and on the evolutive history of each species. In wading birds, a trend to smaller eggs with laying order has been described, but comparative reports are scarce. In this study, egg size variation patterns were described for nine Egrets and Heron species nesting in Birama' Swamp, Cuba. The patterns were described using external dimensions of 3 142 eggs from 1 875 nests of Butorides virescens, Bubulcus ibis, Ardea alba, Nycticorax nycticorax, Nyctanassa violacea and four Egretta species, taken in the field between 1998 and 2006. Results showed that eggs were 4.9-10% of adult weight and had volume variation coefficients between 6-9%. There were no general and consistent interspecies relationship between clutch size and egg sizes. Average volumes tend to get smaller with laying order, but it is not statistically detectable in Butorides and Bubulcus. Last egg was between 0.2% and 15% smaller than the first, showing an inverse relationship with it. Intraclutch asymmetry is light in E. thula and fluctuating around null in Bubulcus. Size only predicted laying or hatching order for the last egg, in nests with more than two eggs, with 72.4% of confidence. [ABSTRACT FROM AUTHOR]

We documented an occurrence of infanticide on a young nestling Florida Grasshopper Sparrow ( Ammodramus savannarum floridanus) while conducting a nest camera study on this critically endangered songbird in south-central Florida. The live nestling was removed from the nest by an adult and died on the ground within 5 hrs of eviction. We suspect that this was a case of parental infanticide based on the behaviors of the infanticidal adult, which were consistent with the breeding female at this nest. The adaptive or nonadaptive motivations for the deliberate eviction of a live nestling remain unknown. This is the first report of infanticide in the Grasshopper Sparrow and the genus Ammodramus. [ABSTRACT FROM AUTHOR]

In gull species, the level of carotenoids in egg yolks is known to decrease along the egg laying sequence. However, the extent of this laying order effect is expected to vary among clutches according to laying date, due to possible differences between early-nesting and late-nesting females with regards to their ability to control the transfer of maternal resources to the eggs. A laying date effect could also result from a seasonal decline in the availability of dietary carotenoids. In this study, we collected data from Yellow-legged Gulls ( Larus michahellis) breeding in southern Tunisia to investigate how nesting date interacts with egg-laying order in shaping patterns of within-clutch variation in yolk lutein, the most abundant carotenoid in this species. In particular, we examined (1) whether yolk lutein concentration declined along the laying sequence and (2) whether the extent of the decline differed among clutches according to laying date. Our results show that yolk lutein decreased along the laying sequence at the clutch level. More interestingly, they also show that the decrease in yolk lutein levels along the laying sequence was more pronounced in late clutches than in early clutches, although lutein levels in adult plasma did not vary according to laying date. Overall, these results support the hypothesis that the Yellow-legged Gull employs the brood reduction strategy and that said strategy is more drastically applied in late clutches than in early clutches. The relevance of female age and seasonal variation in chick-rearing conditions for these findings is discussed. [ABSTRACT FROM AUTHOR]

The number of White Storks ( Ciconia ciconia) has been decreasing in many parts of Europe at least since the middle of the 20th century. Intensification of agriculture and continuous conversion of natural habitats, such as wetlands, into agricultural landscapes have been recognized as the most important determinants of dramatic reductions in population sizes of this species. For this reason, providing quantitative estimates of habitat requirements may allow us to identify the key biota which should be prioritized for conservation. The aim of this study was to investigate White Storks' habitat selection in a mosaic agricultural landscape in central Poland. We found that territories associated with large river valleys were highly preferred by first-arriving storks. We also recorded lower intensity of brood reduction and higher reproductive success of storks breeding in such territories. Thus, it seems likely that location of nests close to river valleys provided easy access to rich food resources associated with wetlands. In fact, distance to nearest wetland was the second strongest predictor of nest-site selection in the studied population. We also demonstrated that pairs nesting in the territories with a high proportion of wetlands showed lower levels of brood reduction in comparison to pairs having poorer access to wet habitat patches. Finally, we found that although early arriving storks avoided settling in an urbanized landscape, they selected nesting sites located close to buildings. The results of this study confirmed high importance of wet grasslands for the core central European population of White Storks. [ABSTRACT FROM AUTHOR]

The article presents a study on the hypothesis that food supplementation would increase reproductive rates of Burrowing Owls. It explains how the researchers supplemented food from clutch completion to brood-rearing of the owls in California. It reveals that supplemented food affected the growth and survival rates of the young and hatchling deaths were higher in nests with non-supplemented food.

Parental food allocation in birds has long been a focal point for life history and parent-offspring conflict theories. In asynchronously hatching species, parents are thought to either adjust brood size through death of marginal offspring (brood reduction), or feed the disadvantaged chicks to reduce the competitive hierarchy (parental compensation). Here, we show that parent American coots ( Fulica americana) practice both strategies by switching from brood reduction to compensation across time. Late-hatching chicks suffer higher mortality only for the first few days after hatching. Later, parents begin to exhibit parental aggression towards older chicks and each parent favours a single chick, both of which are typically the youngest of the surviving offspring. The late-hatched survivors can equal or exceed their older siblings in size prior to independence. A mixed allocation strategy allows parents to compensate for the costs of competitive hierarchies while gaining the benefits of hatching asynchrony. [ABSTRACT FROM AUTHOR]

In many species, embryos are exposed to maternal hormones in utero, in the egg, or in the seed. In birds, mothers deposit substantial testosterone into their eggs, which enhances competitive ability of offspring. These maternal testosterone concentrations vary systematically within clutches in different patterns and may enable mothers to adaptively fine-tune competitive hierarchies within broods. We performed a comparative analysis to investigate this hypothesis using a broad set of avian species. We expected species with small size differences among siblings (arising from small hatching asynchrony or slow growth rates) to aim for survival of the whole brood in good years and therefore compensate last-hatching eggs with relatively more testosterone. We expected species with large size differences among siblings (large hatching asynchrony or fast growth rates) to produce surplus young as insurance against failed offspring and to facilitate elimination of redundant surplus young by bestowing last-hatching eggs with relatively less testosterone. As predicted, we found that maternal testosterone compensation to last-hatching eggs is stronger when size differences among siblings become smaller. Maternal testosterone compensation to last-hatching eggs also correlated negatively with hatching asynchrony and growth rates. These findings provide evidence for correlated evolution of several maternal effects that together support different maternal reproductive strategies. [ABSTRACT FROM AUTHOR]

Altricial birds may vary their relative reproductive investment at the egg versus nestling stages as an adaptive strategy to deal with variable or unpredictable food availability between stages. We investigated the parental investment strategies of Giant Babax ( Babax waddelli) breeding in a harsh, high-altitude environment on the Tibetan plateau. In the modal clutch size of three, egg size declined strongly with laying order, resulting in an intra-brood size hierarchy throughout the nestling period. However, provisioners counteracted the initial handicapping of smaller, last-hatching young by two means: (1) preventing siblings from competing over a predictable feeding site; and (2) preferentially feeding the smallest nestling. Consequently, nestling growth curves differed near significantly by hatching order. We suggest this contrasting investment during the egg and nestling stages may be a strategy to maximize reproductive success in a harsh and unpredictable, high-altitude environment. The handicapping of last-laid eggs provides the opportunity for more efficient brood reduction in unfavorable conditions, but can be counteracted by preferential feeding under favorable conditions. [ABSTRACT FROM AUTHOR]

The article presents the study which examined the effects of brood size, food availability and hatching asynchrony on the fledgling success of the brood of the bird specie, American Coot (Fulica america). In the study, the survival of the chicks was calculated through the use of the Cormack-Jolly-Seber mark-resighting models. The study was conducted in an area near Minnedosa, Manitoba.

We explored the effects of multiple mates on male reproductive success in a species with male parental care in which an increase in the number of female mating partners does not increase the number of eggs received. The broad-nosed pipefish (Syngnathus typhle) has a polygynandrous mating system. In this species, the male cares for embryos in a specially developed brood pouch. During brooding, some embryos fail to develop. We experimentally mated males with either one or two females while keeping brood size similar. We found that broods of singly mated males showed significantly lower embryo survival than those of doubly mated males. Furthermore, larger broods showed relatively lower levels of embryo survivorship independent of number of mates. We conclude that embryo survival is affected by postcopulatory processes that appear to result in higher fitness of multiply mated males. We discuss our results in the light of parental care, sibling competition, genetic benefits, and kin selection. [ABSTRACT FROM PUBLISHER]

No environment is truly constant in time. As a result, animals have evolved multiple adjustments to cope with such fluctuations. However, the allocation of effort to costly activities that imply long-term commitments, such as breeding, may be extremely challenging when future resources change constantly and unpredictably, a context that has received little investigation. To fill this gap, we studied the breeding response by a wetland-dependent raptor, the black kite Milvus migrans, to within and between-years fluctuations in resource availability (inundation levels). The breeding performance of the population was decomposed into reproductive components expressed in a sequence of successive tasks along the breeding cycle (e.g. timing of laying, clutch size, hatching success, brood reduction). Variation in each component was related to resource levels observed at different key dates of the season in order to test whether and when population-level reproduction was adjusted to available resources. Along a 22-year time-series, inundation levels fluctuated unpredictably within and among years, and mostly affected the later components of kites' reproduction, such as hatching success and the incidence of brood reduction, which were the main determinants of the population yearly breeding output. Results were consistent with multiple adjustments to cope with uncertainty. As the season progressed and resources became easier to assess, a bet-hedging waiting strategy based on a conservatively small, invariant and asynchronous clutch gave way to real-time resource-tracking mechanisms mediated by progressive adjustments to current prey availability, so that population-level breeding rates were determined and tuned to resources rather late in the season. Such adjustments were the likely outcome of the interaction between parental tactics and environmental constraints. Behavioural flexibility, such as dietary opportunism, probably promoted further resistance to resource oscillations. Given that all ecosystems show some degree of unpredictability, resource-tracking adjustments, such as the ones depicted here, are likely to be commonplace in most communities. [ABSTRACT FROM AUTHOR]

Clutch and brood reduction is widespread in birds and is mainly caused by lower parental effort during incubation or chick rearing. In black-legged kittiwakes Rissa tridactyla, early chick rearing seems to be more costly for females than males. We, thus, hypothesized that energetically constrained females may be responsible for the low feeding delivery causing brood-reduction. Furthermore, as previous studies have experimentally shown that only females reduce their feeding effort after brood-reduction, we hypothesized that females should decrease their investment after natural clutch or brood reduction. For three consecutive years, we observed parental attendance and feeding behaviour during chick rearing in pairs that hatched only one of their eggs, lost one of their two hatchlings or raised two chicks. We found that in pairs that lost one egg, parents behaved as predicted, with females showing low feeding effort. Furthermore, we found that before brood-reduction, females, but not males delivered less food to their chicks than parents that raised two chicks, and that A-chicks were more aggressive when females delivered less food to them. These results suggest that females may be responsible for brood-reduction. However, after brood-reduction, contrary to what was expected, females did not show lower feeding rate than females raising two chicks. We discuss two non-exclusive potential mechanisms at the origin of this result, namely that brood-reduction may be due to (i) low quality females that are not able to feed their two chicks enough or to (ii) females that adaptively restrained their feeding effort to maximize their residual reproductive value. [ABSTRACT FROM AUTHOR]

The amount of food ingested by chicks has often been suggested as being the main proximate factor controlling broodmate aggression in facultatively siblicidal species. Although several experiments have demonstrated that short-term food deprivation causes a temporary increase in aggression, no study has, to our knowledge, experimentally manipulated overall food supplies and considered long-term effects on chick behaviour and life history traits. We provided supplemental food to breeding pairs of black-legged kittiwakes, Rissa tridactyla, over an entire breeding season and compared the aggressive behaviour of their chicks with that of chicks of control pairs. Control A-chicks (first to hatch) showed more frequent and intense aggression than their experimental counterparts. Furthermore, the more A-chicks begged and the lower their growth rate the more aggressive they were. The consequences of increased aggression for B-chicks (second to hatch) were lower begging rate, lower growth rate and lower survival. We thus provide evidence that a sustained increase in food availability affects broodmate aggression and chick survival at the nest and we discuss the various proximate and ultimate causes involved in the evolution of broodmate aggression. [Copyright &y& Elsevier]

Maternal effects are environmental components of phenotypes that complicate relationships between natural selection and evolution because they often affect phenotypes and fitness simultaneously. We studied the effects of egg size variation on juvenile survival in a population of American coots (Fulica americana). We experimentally evaluated egg size variation at three levels: across the population, within natal nests, and within foster nests. Natal nests accounted for the most variation in population egg size. Within clutches, early-laid eggs were larger than later-laid eggs, with the exception of first-laid eggs, which were small. In the fostering experiment, posthatching survival was most strongly related to egg size relative to natal siblings and natal hatching order and less so to egg size within foster nests. These effects on survival were found even though young from natal nests were neither raised together nor raised by genetic parents. These results indicate that females allocate re- sources unequally among offspring such that offspring from larger, early-laid eggs have higher survival than offspring from smaller, later- laid eggs, regardless of their size relative to foster siblings or to mean population egg size. These results suggest that egg size variation can be maintained through selection on maternal investment strategies and not on egg size per se. [ABSTRACT FROM AUTHOR]

Starvation and enforced virginity induce apoptosis (programmed cell death) in the oocytes of female cockroaches of Nauphoeta cinerea, yet the life-history outcome differs among fed and starved virgins. Consistent with the hypothesis that oocytes are absorbed to reallocate resources, apoptosis is followed by an increase in future reproduction and longevity in starved virgins. However, apoptosis induction by enforced virginity in fed females results in reduced fecundity and longevity. It is predicted that this life-history outcome occurs because oocyte apoptosis under these conditions is not part of an adaptive reproductive strategy but simply is the result of cellular ageing and clearance to maintain reproductive synchrony. In the present study, reproductive and somatic allocation are examined over time to test whether resources are recouped by the fat body, reinvested in reproduction or lost altogether when apoptosis is associated with enforced virginity. To assay reproductive investment, the number of ovarioles is counted, apoptosis levels are analysed and the size of all oocytes within the vitellaerium is measured. To assay somatic investment, dry fat body mass is measured. In conjunction with apoptosis, the number of ovarioles declines, whereas the size of surviving oocytes increases. By contrast to the cellular ageing hypothesis, apoptosis associated with enforced virginity appears to be adaptive if resources from sacrificed oocytes are recycled into the survivors to maintain the quality of ageing oocytes. This reinvestment in current reproduction may trade-off with future reproductive capacity. [ABSTRACT FROM AUTHOR]

Because parental investment for multiple offspring often proves insufficient, diverse taxa have evolved systems for reducing family size secondarily. We found brood reduction to be common (42% of 1000 nesting cycles) in Oklahoma house sparrows, Passer domesticus, especially when families of four or more nestlings were furnished with less food. Whereas deliveries of large-bodied prey have been shown previously to predict long-term survival of nestlings (to breeding age), smaller prey items appear adequate for short-term survival (to fledging). Parents did not prune deliveries in the aftermath of brood reduction, thereby bestowing a likely food bonus on surviving siblings. Individual male and female parents that were observed for multiple nesting cycles produced similar measures of day 11 offspring mass (including largest chick, smallest chick, and brood mean). By contrast, an index of overall sibling mass inequality was not repeatable. Parents skewed food deliveries towards the larger members of relatively passive day 3 broods, probably influencing early mortality: median age for brood reduction was day 4 posthatching. Patterns of allocation that can be inferred from mass inequities of older chicks (on day 11) also pointed to persistently skewed deliveries; nestlings underweight at that age were more likely to die without fledging. Large broods early in the season tended to have nestlings less equally sized than broods late in the season, whereas small broods showed no such season effect. Brood reduction appears advantageous to parents if surviving offspring thereby increase prefledging mass sufficiently to compensate for the drop in numbers. [Copyright &y& Elsevier]

Predation risk is an important factor affecting investment decisions in wild birds. The parental risk-taking response is assumed to depend on the value of the current brood, but to date empirical studies have yielded equivocal results. We tested the ‘reproductive value of the offspring’ (RV) hypothesis by assuming that parents perceive the probability of offspring survival as a significant component of RV. We predicted that survival of offspring as perceived by parents would be inversely related to the level of brood reduction. Accordingly, parents with the same number of offspring may take fewer risks if they have lost offspring than if they have not. We experimentally reduced brood size in a small passerine, the pied flycatcher, Ficedula hypoleuca, and exposed parents to a stuffed sparrowhawk, Accipiter nisus, a predator of adults. For a given brood size, the time elapsed until parents first entered the nestbox after removal of the predator was positively correlated with the level of brood reduction. Parental risk-taking behaviour was not affected by brood size per se when adjusted for the level of brood reduction. No sex-related differences in antipredator responses were found. To our knowledge, this is the first experimental evidence that birds are capable of perceiving brood reduction and of adjusting their antipredator behaviour to the changed value of their offspring. [Copyright &y& Elsevier]

The article presents a study which examines the effect of cowbird parasitism on the probability of brood reduction in the brown-and-yellow marshbird in Pampas, Argentina. It focuses on the comparison between the number of host fledgling produced in parasitized and the unparasitized nests. It discusses the assessment on the effect of year, parasitism, overall brood size, and hatching interval on the probability of brood reduction. It explores the logistic regression model which indicated that hatching interval was the main factor associated with the brood reduction. It highlights the results of the study which support the idea that cowbird egg-laying synchronization imposes additional costs on hosts, as it increases the probability of host brood reduction.