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Highly mobile predators can show strong numerical responses to pulsed resources, sometimes resulting in irruptions where large numbers of young invade landscapes at a continental scale. High production of young in irruption years may have a strong influence on the population dynamics unless immature survival is reduced compared to non-irruption years. This could occur if subordinate individuals (mainly immatures) are forced into suboptimal habitats due to density-dependent effects in irruption years. To test whether irruptive individuals had lower survival than non-irruptive ones, we combined necropsy results (N = 365) with telemetry (N = 185) from more than 20 years to record timing and causes of mortality in snowy owls (Bubo scandiacus), which irrupt into eastern North America during winter following high breeding output caused by lemming peaks in the Arctic. Mortality was more than four times higher in irruption years than non-irruption years, but only for immatures, and occurred disproportionately in early winter for immatures, but not adults. Mortality was also higher in eastern North America, where owl abundance fluctuates considerably between years, compared to core winter regions of the Arctic and Prairies where populations are more stable. Most mortality was not due to starvation, but rather associated with human activity, especially vehicle collisions. We conclude that immature snowy owls that irrupt into eastern North America are limited by density-dependent factors, such as increased competition forcing individuals to occupy risky human-altered habitats. For highly mobile, irruptive animals, resource pulses may have a limited impact on population dynamics due to low subsequent survival of breeding output during the nonbreeding season.

Divorce is widespread among species of birds and may either be an adaptive strategy to secure a better mate or territory or be a nonadaptive result of a failure to maintain the pairbond. I examined the causes and consequences for divorce in the Northern Flicker (Colaptes auratus), a migratory woodpecker with a high annual mortality rate. In a long-term population study of 1,793 breeding pairs over 17 years, the within-season divorce rate was 4.6% and the between-season divorce rate was 15.5%. Retained pairs within a season initiated their renest 5 days faster than divorced birds that had no greater fledgling production, suggesting that within-season divorce was making the best of a bad job with severe time constraints. Poor performance in the year prior to divorce was not strongly associated with divorce, and analysis of multiple breeding stages revealed that divorcing individuals in the subsequent year had later laying dates, smaller clutches, and fewer fledglings than retained pairs but no better performance than widowed individuals. Analyzing the data separately by sex showed that neither males nor females benefitted from divorce. Thus, there is a reproductive cost linked to finding a new partner per se, but no reproductive advantage associated with divorce. New mates after divorce were usually not older (not higher quality) than previous mates, so intrasexual competition was probably not driving partnership splits. The most plausible explanation seems to be a “bet-hedging” hypothesis in which birds re-pair rapidly in spring if their previous mate does not quickly arrive during spring migration. Divorce in Northern Flickers does not appear to be adaptive and future studies on arrival and interactions of individuals in spring will elucidate proximate constraints on relocating the previous partner.

The allocation of prey within broods of altricial nestlings may be the result of parents targeting certain offspring preferentially and/or the result of intrabrood competition related to features of nestlings such as body size. We investigated two mechanisms that could influence allocation of food within broods of Mountain Bluebirds (Sialia currucoides) by filming the size and type of prey that parents fed nestlings. According to the gape size constraint hypothesis, the inability of small nestlings to physically swallow large prey items might place junior brood members at a higher risk of starvation than older siblings if parents do not bring enough small items. Consistent with this idea, the frequency of ‘testing’, placing an item in the gape of a nestling but then withdrawing it, was positively correlated with prey size. The junior nestling of a brood was fed less often when parents brought larger prey items, and nestlings were tested more in the early nestling stage (0–4 days old) when their gapes were smaller than at older stages. Parents of many cavity-nesting species may feed the brood from the nest entrance and the resulting scramble competition among brood members to access the entrance hole also potentially increases the mortality of the least competitive (smallest) nestlings. Although the frequency of feeding from the entrance hole was prevalent during the late nestling stage (≥ 12 days old), feeding from the entrance was not associated with mortality rate in bluebird broods and the mortality of junior nestlings was not linked to the testing of prey. The results confirm that a mechanism of gape size constraint does direct large prey away from junior nestlings, but apparently small-sized prey items were abundant enough during our study so that this did not result in increased mortality of nestlings.

Among species that use similar resources, an individual may benefit by observing and copying the behavioural decision of a heterospecific. We tested the hypothesis of heterospecific social learning in passerine birds, namely that a migrant species, the Pied Flycatcher Ficedula hypoleuca, uses external markings on the nest cavities of a resident species, the Great Tit Parus major, as cues when choosing a nest site. Others have suggested that prospecting flycatchers assess the clutch size of tit “demonstrators” by entering their nest boxes and, assuming that a large clutch indicates a high-quality individual, will copy the nest appearance of tits with large, but not small clutches. During a 4-year period in Norway, we designed a similar study but did not find that flycatchers based their nest choice on the clutch size of tits. Neither were there any relationships between clutch size of the tit and its laying date, incubation behaviour, or the number of eggs visible through nest material during egg-laying so Pied Flycatchers did not use these indirect cues to assess quality of the tutor. Filming of tit nests showed that prospecting flycatchers did not enter tit nest boxes to assess the content. Indeed, incubating female tits only left their nest boxes for short bouts of unpredictable duration so there was little opportunity for flycatchers to inspect the nest contents unnoticed. Our study calls into question the mechanism of using the content of tit nests as public information for choosing traits of nest sites based on external characteristics. We suggest that similar studies of nest site choice in relation to possible social information transfer be replicated more widely.

Many species of birds incorporate feathers into their nest as structural support and to insulate the eggs or offspring. Here, we investigated the novel idea that birds reduce the risk of nest usurpation by decorating it with feathers to trigger a fear response in their rivals. We let prospecting birds choose between a dyad of nest-boxes in the wild, both containing some nest materials, but where one had a few white feathers and the other had none. All three species of cavity-nesting birds studied, the pied flycatcher Ficedula hypoleuca , the blue tit Cyanistes caeruleus , and the tree swallow Tachycineta bicolor , hesitated to enter boxes with white feathers. A similar avoidance of white feathers was found when the alternative nest-box of a dyad held black feathers. However, the birds readily collected white feathers that we placed in front of their nest-box, showing the fear of such feathers was context-dependent. We suggest that naive prospecting birds may perceive feathers in nests as the result of a predation event, and that owners decorate nests with bright feathers that can be seen from the opening to deter others from entering.

Many animals require tree cavities for breeding and these sites may be reused by a diversity of secondary cavity nesters over a timespan of decades. It is unknown whether the reuse of holes changes their desirability as nest sites. We hypothesized that some species, “cavity destroyers,” degrade the quality of holes by filling them with coarse nest material or waste whereas excavating species, “cavity cleaners,” might prolong the use of a hole by removing debris or enlarging the hole. Using data gathered during 22 years from a field study in central British Colombia, we analyzed long-term patterns of cavity occupancy in relation to their sequential use by bird and mammal species, grouped by traits. Patterns of cavity occupancy were variable with 49% of 875 large-sized holes (excavated by northern flickers Colaptes auratus and pileated woodpeckers Dryocopus pileatus) and 19% of 652 smaller-sized holes incorporating runs of sequential use that lasted to 18 years. About 11% of large and 25% of small cavities also had gaps of 3–13 years between occupancies. Mammals, raptors and European starlings, consistent with the hypothesis, were cavity destroyers, occupying cavities as terminal users and before gaps more often than expected by chance. The pattern of occupancy by northern flickers was random in relation to gaps or prior use by other species. Although flickers did not target old holes to clean, neither did they avoid them. Small cavities that were renovated by flickers into larger cavities were reused at twice the rate after renovation. Runs of cavity occupancy that involved only cavity-destroying species were shorter than runs that involved periodic use by flickers, suggesting the woodpecker, through its cleaning and renovation, prolonged the use of such holes. Our study contributes insights on additional ecological factors, namely previous users, that can influence the use and availability of cavities over time. Fil: Wiebe, Karen L.. University of Saskatchewan; Canadá Fil: Cockle, Kristina Louise. University of British Columbia; Canadá. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Puerto Iguazú | Universidad Nacional de Misiones. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Puerto Iguazú; Argentina Fil: Trzcinski, M. Kurtis. University of British Columbia; Canadá Fil: Edworthy, Amanda B.. University of British Columbia; Canadá Fil: Martin, Kathy. University of British Columbia; Canadá

Natal dispersal and local recruitment are affected by factors both intrinsic and extrinsic to juveniles and may affect fitness. Understanding the relationship between dispersal and population density in birds has been hindered by a lack of long-term studies and a focus on resident species has neglected the role of weather operating at large spatial scales. I studied local recruitment and the reproductive consequences of natal dispersal distance within a population of Northern Flickers (Colaptes auratus), a migratory woodpecker. During a field study spanning 16 yr in British Columbia, 8,272 fledglings were banded and 138 males and 105 females recruited locally. The average annual local recruitment rate for males (3.36%) was greater than that for females (2.55%) and the propensity to recruit locally was positively correlated with an early hatch date and high body condition. Annual local recruitment was not associated with population density in the year of hatch but was positively correlated with population density in the year of settlement. Local recruitment was also positively correlated with warmer springs during migration, consistent with the phenology hypothesis that the location of settlement is affected by weather along the route. Among local recruits, natal dispersal distance was independent of the presence of parents and so dispersal was not a behavior to prevent inbreeding. However, settling closer to the natal site led to reproductive benefits in terms of earlier laying dates and better nest success. Therefore, juveniles may gain useful information about the location of nesting substrates, predation risk, and patchy food resources by exploring the landscape around their natal site during the post-fledging period and then settling in the familiar area after returning from migration.

Interspecific competition is expected when two species share resource needs. For example, secondary cavity‐nesting birds may compete vigorously for suitable nest sites both within and among species. However, little is known of whether monogamous species defend more than one nest site on their territory after breeding has begun, and in particular whether they are aggressive against other species. Defending extra nest sites may be adaptive because they may be used for renesting after a failure or to produce a second brood. We studied interactions between a monogamous, resident bird, the great tit Parus major and a migrant, the pied flycatcher Ficedula hypoleuca, providing nest boxes in woodlands in Norway. Agonistic behaviours may be subtle and easily overlooked so we experimentally placed caged male pied flycatchers near nests of great tits and at a dyad of empty nest boxes erected in the territory 25 m away. We filmed interactions between species at 21 sites in the egg‐laying period of the tit, and at 26 nest sites during incubation. Male great tits showed aggression towards the caged flycatcher both at their own nest box and at the nest boxes erected at a distance. We manipulated the external appearance of the nest boxes with painted designs around the entrances but the intensity of aggression at the empty nest boxes did not depend on whether those boxes matched the nest box with the tit nest and was not correlated with tit clutch size. Neither was the intensity of display activity at each nest box by the flycatchers that settled associated with these variables. The results are discussed in relation to hypotheses for nest site choice involving interspecific social learning and aggression.

Age-related improvement in reproductive performance is widespread in vertebrates and constraints at young ages are a common cause. The sex that invests energetically more in reproduction, typically the female, is predicted to show stronger age-related performance but the effect of the male's age on reproduction has often been ignored. I studied age-related reproduction of both sexes in northern flickers, in which males invest more parental care than females, predicting that the effect of age would be stronger in males than in females. Longitudinal data on individuals collected during an 18-year field study confirmed this prediction. Laying dates for females improved only between the first 2 years of her life and no other reproductive parameter changed over her lifetime when the male's age was statistically controlled. In contrast, males improved up to age five for laying date, clutch size, hatching success and fledging success. Partner familiarity (fidelity) was further associated with earlier laying, larger clutches, improved fledging success and more fledglings. There was significant assortative pairing by age but there is apparently little benefit for males to choose older females, but a benefit to females with older males. Females appear to strategically lay larger clutches when paired to old males which invest more in paternal care than younger males. This is the first example of clutch size being influenced by only male age and not female age in any bird and suggests that sex roles in parental care are important determinants of aging patterns in vertebrates with diverse life histories.

Meeting energy requirements during the nonbreeding season is important for many animals and some defend winter territories to secure a food supply. In birds of prey, females, the larger and competitively dominant sex, may monopolize areas with higher prey abundance than males. We thus predicted that female Snowy Owls (Bubo scandiacus (Linnaeus, 1758)), which might acquire the high-quality habitats and individuals in better body condition, would be able to persist on smaller home ranges, travel shorter distances, and spend proportionally more time on a home range than males, during the winter. On the prairies in central Saskatchewan, we deployed satellite transmitters on 11 male and 12 female Snowy Owls over two winters. There were no significant differences between the sexes in home-range size or the amount of travelling during the winter months. Mean first home range (95% minimum convex polygon) size was 54.4 km2 for males, 31.9 km2 (estimated marginal means) for females, and 53.8 km2 for the sexes combined. However, within sexes, home-range size was negatively correlated with body condition as predicted. A lack of defense of home-range perimeters against conspecifics could increase variation in home-range size and movement patterns and reduce differences between the sexes.

Natal dispersal is common in animals but the fitness cost of moving from the natal area is not well understood. One reason for a fitness cost is that foraging skills and prey preference learned early in life may be less efficient if the individual settles in a new, unfamiliar habitat. In a 4-year study, we found that immigrant parent blue tits, Cyanistes caeruleus, and great tits, Parus major, were inferior food providers compared to local recruits. In blue tits, immigrants provided smaller prey items than local recruits, whereas in great tits, the immigrants provided fewer green larvae, but relatively more brown larvae, to the offspring than local recruits. We also found that immigrant females laid later or smaller clutches than females locally recruited. The results are consistent with the hypothesis that natal dispersal carries costs related to the learning of foraging skills. However, alternative explanations are that the differences were caused by genetic and/or quality differences between the two groups of birds. We discuss various ecological and behavioural traits that may influence, and be influenced by, the mismatch of foraging between natal and breeding habitats. In altricial birds, yearlings will not have previous foraging experience during breeding and, in addition, immigrants will not have spent a long postfledging period in the new local habitat with their parents. If there are foraging-habitat mismatches as a result of dispersal, researchers should include natal origin in models of optimal foraging, time budgets, reproductive success and survival because performance may be directly related to the early learning environment rather than genetic differences.

Woodpeckers are considered ecosystem engineers because they excavate tree cavities which are used subsequently by many species of secondary cavity nesters for breeding. Woodpeckers have the choice of excavating a new hole or reusing an existing one, and this propensity to excavate (e) may affect community dynamics but has rarely been investigated. Using 18 years of data on a population of northern flickers Colaptes auratus, I tested six hypotheses to explain the propensity to excavate (e) in a landscape which experienced two types of disturbance: pine beetles and wildfires. Woodpecker age, breeding experience and mate retention had little influence on e which varied between 13-39% annually and averaged 23% for 1843 first nests over the 18 years. Body size and body condition of males and females were not associated with e but rates of excavation declined seasonally, suggesting time rather than energy costs limited excavation effort. Reduced cavity availability mediated through high conspecific density coupled with wildfires triggered relatively high excavation rates, up to 39% but e decreased to baseline levels three years after the landscape disturbances. Nearly 2/3 of males did not excavate in their lifetime but apparently, e is great enough to balance the average rate of cavity tree loss in this forest which is 11% annually. Excavation propensity in flickers is flexible, but the birds reduce their work levels if there is a surplus of holes available. This article is protected by copyright. All rights reserved.

Hybridization can bring in single individuals alleles that were never designed to work together, which can result in unexpected or transgressive phenotypes. The Yellow-shafted (auratus group) and Red-shafted (cafer group) subspecies groups of the Northern Flicker (Colaptes auratus) differ conspicuously in the coloration of their flight feathers, but hybridize freely where their ranges overlap in western North America. The difference in color is largely the result of the Red-shafted form harboring ketolated products at C4(4′) of the carotenoids found in the Yellow-shafted form. Characterizing the carotenoid pigments in a series of birds of intermediate color (presumed hybrids) revealed that most accumulated a product of β-cryptoxanthin with a keto group on its hydroxylated ring (3-hydroxy-echinenone), while a few accumulated the product with a keto group on the unhydroxylated ring (3′-hydroxy-echinenone). Surprisingly, the latter group also had feather barbs that were noticeably yellower than the associated rachis, corresponding to a lower level of ketolation at C4(4′). We assessed possible biochemical explanations for the differences by probing the relative carotenoid concentration data in individuals of varying color. The difference between the hybrids could not be explained by the general level of ketolation of carotenoids or a particular selectivity of the 4-ketolase involved. We present a testable genetic explanation that invokes incompatibilities between divergent alleles of the two parental forms at interacting loci. Because the idiosyncrasies affect oxidation, they may be the product of mitonuclear incompatibilities.

Birds that winter in cold northern climates experience harsh conditions, including reduced food availability and increased energy demands. In raptors, the ability to forage and maintain body condition may be related to age (hunting experience) or the ability to defend good-quality territories (dominance). We examined the effects of age and sex on body condition and various sources of mortality in wintering Snowy Owls (Bubo scandiacus) on the Canadian prairies. Because of reversed sexual size dimorphism, we predicted that females, the dominant sex, would be in better condition than males and that adults would be in better condition than juveniles. Consistent with these predictions, data from 537 live Snowy Owls trapped over 18 winter field seasons showed that adults were heavier than juveniles for a given body size and carried more fat reserves. We found that 56% of males lacked furcular and wing-pit fat, whereas only 31% of females lacked such fat; and females, but not males, tended to put on fat...

Interspecific competition over nest sites is common among cavity-nesting birds, but little is known about what determines the outcome of such contests, particularly whether or not prior ownership plays a role. Using a box removal and replacement experiment, I tested whether Mountain Bluebird (Sialia currucoides) or Tree Swallow (Tachycineta bicolor) had the higher resource holding potential (RHP). A different box-blocking experiment with paired boxes on territories measured the extent to which prior ownership influenced contest outcomes for both species. Behavioral observations in the pre-laying period showed more physical aggression by Mountain Bluebird against Tree Swallow. Nevertheless, Tree Swallow won 70% of boxes when neither species had prior ownership, suggesting Tree Swallow had a higher RHP. When their boxes were blocked, 24% of Tree Swallow usurped boxes from Mountain Bluebird, which did not differ statistically from the 33% of boxes usurped by bluebirds from swallows; thus, prior owne...

Carotenoid-based colouration in feathers is widely accepted to be a reliable signal of the health of an individual, but the condition-dependence of melanin-based plumage ornaments has been highly debated. Using broods that were manipulated in size, we tested whether nutritional stress during rearing affected the carotenoid pigmentation in secondary feathers and the size, shape, and symmetry of melanin spots on breast plumage of northern flicker Colaptes auratus nestlings. Two measures of carotenoid colour (chroma and brightness) of secondary flight feathers did not vary according to brood size treatment, but in a larger dataset from the population, carotenoid chroma was positively associated with nestling mass. Nestlings from experimentally enlarged broods had smaller melanin spots than those from reduced broods, which is some of the first experimental evidence that melanin ornament size in growing nestlings is condition-dependent. However, the shape and symmetry of the melanin breast spots was not associated with nestling mass. Sexual dimorphism was apparent in both types of pigmentation and future studies should investigate whether there are any trade-offs for nestlings between investing in carotenoid colouration and melanisation and whether trade-offs differ between the sexes.

Optimal foraging theory suggests that avian parents should prefer the most energetically efficient (largest) prey items when delivering food to offspring at a central place. However, during periods of high demand, selectivity of prey may decline, leading to the delivery of smaller and/or less nutritious items. We compared foraging trade-offs between great tits (Parus major) which had a wider feeding niche than blue tits (Cyanistes caeruleus). We also compared the foraging efficiency of cross-fostered young, which had learned the spatial foraging niche and prey size of the foreign species, to that of control conspecifics. Mean delivery rates did not differ between control and cross-fostered parents of either species but as delivery rates increased, prey size declined for both species and both treatment groups. However, across the range of increasing delivery rates, parents were able to increase the total biomass of prey delivered. Cross-fostering did not alter the proportion of different prey taxa in the diet, but cross-fostered birds shifted the size of the prey taken to that of their foster species. Consistent with their broader feeding niche, great tits, but not blue tits, incorporated more unpalatable items (flies) as delivery rates increased. Although great tits foraged less efficiently in the blue tit niche, paradoxically, blue tits seem to deliver more prey biomass when foraging in the great tit niche.

Nest sanitation is an understudied form of parental care that may improve offspring fitness by reducing microbes and ectoparasites in the nest. Many species clean nests, but it is unknown whether parents respond flexibly to various costs and benefits when deciding how much effort to invest. We experimentally manipulated brood size in the short term and in the long term in a cavity nester, the northern flicker, Colaptes auratus, to test whether parents alter their sanitation effort in response to brood demands. Males generally removed more faecal sacs than females at all treatments and in most cases, faecal removal rates were proportional to feeding rates in control and experimental broods. The rate of sac removal was negatively correlated with feather corticosterone in females but not in males. Males maintained higher faecal removal rates than females to enlarged broods and were more flexible than females in altering their sanitation effort relative to their feeding rate. Single males, but not females, removed fewer faecal sacs than paired males, suggesting that males reduce nest sanitation effort in times of high nestling demands if it helps maximize fledging success. Across taxa, the sex that invests the most in other forms of parental care also seems to perform more nest sanitation, and future studies should test how parents value it differently depending on brood demands and intrinsic factors.

Elucidating the processes that create species differences is a central goal of evolutionary biology. The Northern Flicker (Colaptes auratus) exists as two well-differentiated subspecies groups in North America, the Yellow-shafted (auratus group) and Red-shafted Flickers (cafer group), which differ strikingly in the color of the underside and rachises of flight feathers, and of malar and nuchal patches. We investigated the physiological basis of these conspicuous phenotypic differences by identifying and quantifying the pigments involved. The yellow feathers of auratus contained carotenoids commonly found in nature (lutein, β-cryptoxanthin, zeaxanthin and β-carotene). The orange to red shafts/vanes of cafer and hybrids contained these carotenoids as well as mono- and diketo-carotenoids (notably adonirubin, α-doradexanthin, canthaxanthin, astaxanthin), representing oxygenated products at carbon C4(4') of the carotenoids present in auratus. Oxygenation of feather carotenoids at C4(4') correlated closely with shaft/vane redness. Carotenoid hydroxylation at C3(3') and the proportion of carotenoids with ε end-rings also varied with color and belie differences in the activity of several carotenoid-modifying enzymes between the two subspecies groups. Curiously, occasional yellow feathers in red-shafted individuals had the carotenoids of auratus, hence the differences are not constitutive in cafer, underscoring regulatory differences. The red malar stripe of cafer, the black malar stripe and red nuchal patch of auratus all contained similar types and amounts of carotenoids, mostly 3-hydroxy-4-keto-carotenoids. The biochemical differences between two strongly differentiated forms we uncovered shed light on how plumage coloration can change over evolutionary time and point to further avenues of research.

Melanin is a common pigment in the plumage of birds, but the extent to which its deposition in feathers is condition dependent and can be used as a reliable signal of quality and reproductive performance is still much debated. In addition, the existence and function of melanin ornaments in female birds or in birds of different age classes has rarely been addressed. We studied the size and color of 4 melanin ornaments in the Northern Flicker (Colaptes auratus), a woodpecker, and found that the plumage patches became larger or darker with age class in both sexes. Consistent with the partly reversed sex roles of Northern Flickers and sexual selection in both sexes, several melanin ornaments were the same size in males and females and were correlated with body size or body condition. There was assortative pairing according to melanin ornaments when controlling for age, and 1 or more ornaments predicted laying date or clutch size of the pair independent of age. The results suggest that melanin ornamen...

This research has been accepted and published in the Journal of Avian Biology. © 2017 Wiley

Foraging with others can reduce predation risk but may increase competition for resources. Species, sex, or age classes may use different niches to reduce competition for food, which may be enforced by social dominance or may lead to ecological specialization. An alternate hypothesis is that individuals using resource patches that renew over time intentionally avoid recently depleted patches by avoiding each other. We tested these hypotheses by simultaneously radio-tracking northern flicker (Colaptes auratus) mates. Members of a pair rarely foraged in the same patch, spending over 90 % of the time >50 m apart. Counter to the ecological specialization hypothesis, the types of ground cover used for foraging and the distance of foraging patches from cover and edge did not differ between males and females. Mates were more spatially segregated on the home range than random and males foraged closer to the nest than females, but we never saw agonistic behaviors counter to the dominance hypothesis. Both sexes avoided returning to the same foraging location repeatedly, perhaps because of prey depletion. We suggest that members of a pair avoided foraging close to each other to reduce encounters with depleted prey patches. We emphasize the importance of simultaneous tracking of mates to identify foraging strategies and potential niche segregation at the home range scale.

Brood enlargement experiments have been conducted in several species of birds to investigate how parents of both sexes adjust their investment in the current breeding attempt. We studied parental feeding effort in the Northern Flicker (Colaptes auratus), a species with partially reversed sex roles where males invest more in parental care than females and in which there is facultative polyandry and no extra-pair young. By experimentally manipulating brood sizes to be either larger or smaller by about 40%, we tested the flexibility of provisioning responses by each sex and whether the upper limit to provisioning corresponded to the maximum clutch size in the population. Both male and female parents increased feeding rates to enlarged broods, but per-nestling provisioning declined so that they fledged lighter nestlings with shorter wings. Mortality in reduced broods was lower than in control broods, but there was no difference in the incidence of mortality between control and enlarged broods. Parent...

The importance of cavities as roost sites in migratory species is often unknown because it is challenging to monitor cavity use during the non-breeding period. We documented cavity use throughout the annual cycle of a woodpecker using light-level geolocators. Northern Flickers Colaptes auratus spent 63–90% of nights roosting in a cavity throughout the year, including during migration. The high frequency of year-round cavity use by Flickers suggests that cavities provide benefits beyond nest-sites. Our work highlights the potential use of geolocators to examine cavity use.

Census-based studies document changes in population size of animal species in response to wildfires, but mechanisms involving behavior of individuals and the effects on reproductive success are usually unknown. I developed a conceptual model explaining the persistence of cavity-nesting birds on the landscape after fires depending on carrying capacity (food supply) of the habitat and the philopatry and territoriality of the species. The breeding density, nest site characteristics, and reproductive success of Northern Flickers Colaptes auratus was studied before and after low- to moderate-severity fires on replicated plots. The density and spatial distribution of nests did not change in a consistent way after fires, but the rates of cavity excavation increased and characteristics of nest sites changed as such decay class of the tree. Laying dates were delayed and clutches were smaller in freshly excavated vs. reused cavities on the burned sites. Breeding philopatry caused a shift to older age classes in the population. Depredation of nests by small mammals increased during the first three years after fires, reducing the number of young produced per nest attempt on burned plots. The study shows that, even when fire does not reduce the density of breeding pairs, there may be detrimental effects detected only by monitoring the behavior and reproduction of individuals.

Manipulations of brood size measure the willingness or ability of parents to invest in offspring and different reproductive roles may lead to differences in feeding effort between the sexes. Parental investment in birds is usually assessed by quantifying feeding rates, but this provides an incomplete picture of parental effort because it fails to account for how parents collect food on the landscape. We studied northern flickers (Colaptes auratus), a woodpecker in which males provide the majority of parental care and used a repeated measures design and short-term (24 h) brood enlargements (N = 35) and reductions (N = 27) to assess effects of treatment on feeding rates to nestlings and parental foraging behaviour. Parents of enlarged broods did not significantly increase feeding rate, resulting in a decline in nestling mass. Parents of reduced broods decreased their feeding rates by 84%, but increased per capita feeding rates, resulting in nestling mass gain. The variation in feeding rates to enlarged broods was not influenced by feather corticosterone, body condition, feather re-growth rate or mass change between the incubation and nestling periods. Foraging pattern on the landscape remained the same during the enlarged treatment for both sexes. We conclude that flickers respond to proximate cues in brood demands, but do not increase feeding rates to enlarged broods, at least in the short term. A literature review suggested that this lack of response is atypical for short-lived species. We hypothesize that parents in species with large home ranges and long nestling periods face energetic limitations that constrain their ability to respond to enlarged broods. We encourage future studies to assess foraging behaviour on the landscape to document important trade-offs for parents such as predation risk and energy expenditure while feeding offspring.

Sexual conflict is magnified during the post-fledging period of birds when the sexes face different trade-offs between continuing parental care or investing in self maintenance or other mating opportunities. Species with reversed sex roles provide a unique opportunity to study the relationship between mating systems and investment in parental care. Here, we provide the first detailed study of the length of care by males versus females (n = 24 pairs) during the post-fledging period, assessing factors that may promote care within and between the sexes. In the northern flicker Colaptes auratus, a species with partly reversed sex roles, males cared longer than females (average 16 versus 12 days, respectively). Overall, 36 % of females but no males deserted the brood prior to fledgling independence. Parents that provisioned nestlings at a high rate also spent more days feeding fledglings. Among males, age and nestling feeding rates were positively associated with the length of care. Among females, a low level of feather corticosterone (CORTf) was associated with a longer length of care. About 45 % of fledglings died within the first week, but fledglings with intermediate body mass had the highest survival suggesting stabilizing selection on mass. Fledgling survival was also higher in individuals with larger broods and lower levels of CORTf. We demonstrate that because females can be polyandrous they often desert the brood before males, and that the sexes respond to different cues relating to their energy balance when deciding the length of care given to their offspring.

As offspring grow, parents often feed them with different sizes or taxa of prey to suit the changing nutritional or energetic demands. We investigated whether such changes in prey types were innate and inflexible or whether they were based on the proximate cue of offspring size. We created experimental broods in which parent blue tits Cyanistes caeruleus and pied flycatchers Ficedula hypoleuca received either older nestlings simulating rapid development or younger nestlings simulating delayed development. The size of prey increased over time in all brood types, suggesting a strong programmed pattern of foraging by parents. However, delayed broods were provisioned with smaller prey than control or advanced broods indicating some plasticity in the response by the parents to the size of nestlings. Although female birds brought smaller prey than male birds, both sexes showed the same rate of increase of prey size with time and brought similar types of prey items. The proportion of soft, digestible larva prey in the nestling diet decreased over time in pied flycatchers but increased in blue tits. Counter to the hypothesis that spiders provide unique and preferred nutrients for young nestlings, the proportion of arachnids in the diet did not change with nestling age for either species. The lack of treatment effect on the taxa of prey delivered suggests that temporal shifts in diet composition are not driven by the proximate cues of nestling age or size but that the feeding patterns are fairly innate and fixed in these altricial birds.

The post-fledging dependency period of birds is often characterized by high juvenile mortality, but fledglings in specific habitats may have increased survivorship. We describe habitat use by fledgling northern flickers (Colaptes auratus) in relation to the availability of patchy forest and prairie habitat in central British Columbia, Canada. We used radiotelemetry to monitor survival of fledglings according to their use of habitats during the dependency period. The fledglings occupied habitats with a higher density of trees than either random locations or nest sites and they switched from forested areas to more open grasslands after 7–10 days post-fledging. Some moved >1 km from the nest within 4 days post-fledging. Fledglings from nests in small tree clusters with little forest cover within 250 m moved farther from their nest within the first 4 days post-fledging than fledglings from nests in larger forest patches. Fledgling survival was positively correlated with the amount of canopy cover and negatively correlated with the amount of forest cover at the larger landscape scale. Young flickers moved among habitat types, which may occur as a result of trade-offs between predation risk and food abundance between habitats. We conclude that fledgling flickers at younger ages used dense forested areas and grassland habitat and forest at older ages to maximize survival and to access food sources. Maintaining patches of dense cover and the amount of forest cover on less than 35% of the landscape may improve fledgling survival of flickers. © 2014 The Wildlife Society.

Few studies have reported flight responses of prey on landscape slopes in the wild, and little theoretical work is available. We present a formal model to predict whether prey should move up or down the hillside after detecting a perched raptor as determined by the duration of the attack once launched by the predator, perching height of the predator, and the landscape slope. We recorded escape responses of blue tits Cyanistes caeruleus and great tits Parus major when approached by a human in the field. This was done in the postfledging period, when the demand for food is high, and when the families usually move to a new site, presumably perceived to be safer, to continue foraging after being exposed to a predator. We found that great tit families, which prefer to forage close to the ground, flew uphill, matching the model’s prediction. However, blue tit families, which forage higher in the canopy, did not move uphill but moved higher up in the trees. Vertical movement upward may be the safest option if the predator is located on the ground. Modeling escape flights may encourage detailed studies of attack and escape behaviors in animals and provide insights in predator–prey interactions in general.

Sexual size dimorphism can result in reduced competition if it leads males and females to use different foraging techniques or consume different prey items. Among woodpeckers, differences between males and females in bill length are common and may explain foraging differences in this family of birds. Northern Flickers (Colaptes auratus) are ground-foraging woodpeckers that specialize on ants. However, the overall contribution of ants to their diet and the proportions of particular ant genera in their diet are not well known. To understand the relationship between bill morphology and the consumption of prey items, we compared the bill length and bill width of male and female flickers. We then collected and analyzed fecal samples from breeding flickers (N = 40 males, 33 females) at a study site in central British Columbia, Canada. Bills of male flickers were significantly longer (4%) and wider (5%) than those of females. Of 11 prey types identified, ants made up over 99% of their diet, and the abundance and composition of ant taxa in the diet did not differ between the sexes. We found significant year and time of season effects, with the abundance of Tapinoma sessile and Lasius spp. increasing from May to the end of June and differing between years. This difference in diet composition between years may have been due to changes in the abundance or accessibility of certain ant taxa related to differences in vegetation structure or weather. Nine ant taxa were consumed by flickers and the four most common were T. sessile, Lasius spp.,Myrmica spp., and the Formica fusca species group. The degree of dimorphism in bill size of male and female Northern Flickers in our study was smaller than reported for several species of arboreal-foraging woodpeckers, suggesting that bill size of ground-foraging woodpeckers may not be strongly linked to niche separation at the level of prey selection. RESUMEN La falta de segregacion en la dieta de machos y hembras de Colaptes auratus alimentandose de hormigas durante la epoca reproductiva El dimorfismo sexual puede resultar en una reduccion en la competencia si conduce a que machos y hembras utilicen diferentes tecnicas de forrajeo o a consumir diferentes tipos de presas. Entre los pajaros carpinteros, las diferencias entre machos y hembras en la longitud de su pico son comunes y pueden explicar las diferencias en el forrajeo en esta familia de aves. Colaptes auratus son pajaros carpinteros que forrajean sobre la tierra y que se han especializado en consumir hormigas. La contribucion de las hormigas a su dieta y las proporciones de determinados generos de hormigas en su dieta no son bien conocidos. Para entender la relacion entre la morfologia del pico y el consumo de presas, comparamos la longitud y el ancho del pico de machos y hembras de C. auratus. Despues, colectamos y analizamos muestras fecales de C. auratus que estaban en estado reproductivo (N = 40 machos, 33 hembras) en un sitio de estudio en el centro de Columbia Britanica, Canada. Los picos de los machos fueron significativamente mas largos (4%) y anchos (5%) que los de las hembras. De los 11 tipos de presas identificadas, las hormigas contribuyeron a mas del 99% de su dieta, y la abundancia y composicion de los taxones de hormigas en la dieta no fueron diferentes entre los sexos. Encontramos efectos significativos en el ano y en la parte de la temporada, con la abundancia de Tapinoma sessile y Lasius spp. aumentando desde mayo hasta el final de junio y difiriendo entre anos. Esta diferencia en la composicion de la dieta entre anos puede haber sido debido a los cambios en la abundancia o en la accesibilidad de ciertos taxones de hormigas, relacionadas con diferencias en la estructura de la vegetacion o del clima. Nueve taxones de hormigas fueron consumidos por C. auratus, de los cuales los cuatro mas comunes fueron Tapinoma sessile, Lasius spp., Myrmica spp. y el grupo de especies de Formica fusca. El grado de dimorfismo en el tamano del pico de machos y hembras de C. auratus en nuestro estudio fue menor que lo reportado para varias especies de pajaros carpinteros que forrajean en los arboles, lo que sugiere que el tamano del pico de los pajaros carpinteros que forrajean sobre la tierra no esta fuertemente ligado a la separacion de nicho a nivel de seleccion de presas.

Foraging theory suggests animals should prefer habitats with a greater density of prey, but few have investigated whether birds change foraging habitats according to short-term changes in prey abundance caused by weather. We studied a woodpecker, the northern flicker (Colaptes auratus), in which the diet is composed mainly of ants collected on the ground surface. We measured the surface density of the ant prey in 1-m2 quadrats placed in 2 habitat types that had different thermal properties: open grassland and forest. The density of ants varied according to year of the study, habitat type, date during the summer, and time of day and was strongly associated with ambient temperature. In the shaded forest habitat, ant density increased linearly with air temperatures between 6 and 28 °C In contrast, the surface activity of ants in the open habitat exposed to sun began to decline once ground surface temperatures reached 26 °C Ant densities were higher in the open habitat than in the shade in relatively...

Recent research on reproduction in animals has emphasized phenology and prey matching in the long term and on large spatial scales (e.g., linked to global climate change). We studied how individuals within one reproductive cycle and at small spatial scales may try to maximize access to food resources that vary in space and time. Herbivorous mammals are known to track favorable phenological stages of their food plants and move seasonally on the landscape. Whether phenology similarly affects spatial movements of birds on their breeding grounds is largely unknown. We studied postfledging movements of Blue Tits (Cyanistes caeruleus) and Great Tits (Parus major) when the young were escorted by parents during 19 to 43 days posthatching. This was done over 4 years in a 1.6-km2 woodland area in Norway in which an elevational gradient (105–266 m) caused a phenological delay in vegetation and peak abundance of caterpillar prey at the higher elevations. Postfledging movements were similar in the two tit sp...

Parents of altricial young alter provisioning effort based on offspring demand, but life-history differ- ences between the sexes can influence the willingness of each parent to invest in a brood. Previous studies on sex- specific provisioning roles in altricial species suggest a wide range of responses by males and females, which vary depending on the life history of the species. The Northern Flicker (Colaptes auratus) is unusual among altricial birds, as it has partly reversed sex roles with males investing more in parental care than females, it has no-extra-pair young, and it engages in facultative polyandry. We inves- tigated sex-specific provisioning patterns to see what fac- tors (brood size, nestling age, adult age, body condition, nestling sex ratio and partner provisioning level) affected provisioning rates. Additionally, we determined nestling growth rates and estimated nestling energetic demands. Based on 232 filmed provisioning bouts at 82 nests, we found that males provisioned 1.11 times more than females. In addition, provisioning rates by males were primarily associated with nestling age, female provision- ing, brood size, and body condition. Provisioning by females was more strongly related to the male's provi- sioning effort and brood size. Per capita provisioning rates decreased with brood size, resulting in lighter nestlings in large broods. Our results suggest that both parents responded to the changes in brood demands, but do so governed by different factors. We suggest that the rela- tively high provisioning by males is related to high male assurance of paternity.

Parent birds respond to a variety of cues from their offspring when provisioning them with food. Bright flange colours and large body size are two traits of offspring that many parents seem to favour, but little is known about how such traits interact. By experimentally altering the difference in mass between nestmates while concurrently blackening the flanges of either the large or small nestlings in the brood, we tested whether large body size could compensate for dull coloration. In three species of cavity nesters (northern flicker, Colaptes auratus, great tit, Parus major, and pied flycatcher, Ficedula hypoleuca), doubly disadvantaged offspring that were both small and dull performed the worst, whereas large and bright offspring received the most provisioning, consistent with the idea of additive effects. We used regression to show that, for flickers, dull (blackened) nestlings performed as well as bright nestlings when they were 20% larger than their bright nestmates. For passerines, dull nestlings had to be 30–40% larger than bright nestlings to receive equivalent amounts of food from parents. Within-brood differences in mass before manipulation were often greater than this size difference threshold, suggesting that hatching asynchrony has a stronger influence on food allocation than do colour differences among siblings.

Tree cavities are a vital multi-annual resource used by cavity-nesting birds and mammals for nesting and shelter. The abundance of this resource will be influenced by the rates at which cavities are created and destroyed. We applied the demographic concepts of survival and longevity to populations of tree holes to investigate rates of loss for cavities in three tree species, as well as how characteristics of nest trees, habitat type, and species of excavator affected the persistence of tree cavities in trembling aspen, Populus tremuloides (95% of cavities were in aspen trees), in interior British Columbia, Canada. By modeling survival of 1635 nesting cavities in aspen over a time span of 16 years, we found that the decay stage of the nest tree was the most important factor determining cavity longevity. Cavities in trees with advanced decay had a relatively short median longevity of 7 years (95% CI 6-9 years), whereas those in living trees had a median longevity of more than 15 years. We found that cavity longevity was greater in continuous forest than in aspen grove habitat. Interestingly, cavities formed by weak excavators survived as long as those created by Northern Flickers (Colaptes auratus), despite occurring in more decayed tree stems. Thus, weak excavators may be selecting for characteristics that make a tree persistent, such as a broken top. Our results indicate that retention of cavities in large, live aspen trees is necessary to conserve persistent cavities, and that cavity longevity will have a large effect on the structure and function of cavity-using vertebrate communities.

We report an unusual case of a monogamous pair of Northern Flickers (Colaptes auratus) initiating a second clutch while there were still nestlings in the first nest. The male and female incubated at both nests but only the male fed nestlings at the first nest. The second nest attempt was abandoned after the first nestlings fledged, possibly because the two broods were too synchronous in timing for the male to contribute sufficiently to both. Double-brooding has not been previously documented for Northern Flickers.

1. Climate warming has led to shifts in the seasonal timing of species. These shifts can differ across trophic levels, and as a result, predator phenology can get out of synchrony with prey phenology. This can have major consequences for predators such as population declines owing to low reproductive success. However, such trophic interactions are likely to differ between habitats, resulting in differential susceptibility of populations to increases in spring temperatures. A mismatch between breeding phenology and food abundance might be mitigated by dietary changes, but few studies have investigated this phenomenon. Here, we present data on nestling diets of nine different populations of pied flycatchers Ficedula hypoleuca, across their breeding range. This species has been shown to adjust its breeding phenology to local climate change, but sometimes insufficiently relative to the phenology of their presumed major prey: Lepidoptera larvae. In spring, such larvae have a pronounced peak in oak habitats, but to a much lesser extent in coniferous and other deciduous habitats. 2. We found strong seasonal declines in the proportions of caterpillars in the diet only for oak habitats, and not for the other forest types. The seasonal decline in oak habitats was most strongly observed in warmer years, indicating that potential mismatches were stronger in warmer years. However, in coniferous and other habitats, no such effect of spring temperature was found. 3. Chicks reached somewhat higher weights in broods provided with higher proportions of caterpillars, supporting the notion that caterpillars are an important food source and that the temporal match with the caterpillar peak may represent an important component of reproductive success. 4. We suggest that pied flycatchers breeding in oak habitats have greater need to adjust timing of breeding to rising spring temperatures, because of the strong seasonality in their food. Such between-habitat differences can have important consequences for population dynamics and should be taken into account in studies on phenotypic plasticity and adaptation to climate change.

We investigated whether a mechanism of gape size limitation could increase the competitive ability of a large brood parasite in a brood of smaller host nestlings. The gape size of hatchling birds may limit the size of prey they can swallow and hence parents should bring larger more profitable prey as their nestlings grow. The relatively large gape of a brood parasite in a brood of smaller hosts may 1) increase provisioning rate to the brood, 2) allow the parasite to swallow large prey, or 3) cause parents to start bringing larger prey at an earlier nestling stage. We added 1 large same-aged great tit Parus major nestling to broods of smaller blue tits Cyanistes caeruleus to simulate a naive brood parasite system and filmed them when 2–3 days old. The cue of a single large nestling did not cause parents to increase provisioning rates nor to change the species of prey, but prey items were larger than in control broods. Large prey were "tested" more often than small prey, that is offered and then removed from the gapes of small nestlings, and 17% of the prey that the great tit nestling received had been previously offered to a blue tit. Our results revealed that prey size brought by parents could further increase the competitive ability of brood parasites.

We investigated the effect of spring temperatures, female age, and female body condition on the timing of laying in a migratory woodpecker, the Northern Flicker (Colaptes auratus), and looked at the relationship between laying date and reproductive success. Average annual laying dates in the population, recorded over 12 years, were not related to the North Atlantic Oscillation or the Pacific-North American climate indices but were earlier when average daily temperatures along the migration route of Northern Flickers along the Pacific coast of North America were warmer. However, the strongest negative correlation between laying dates and ambient temperatures occurred after the arrival of most birds on the breeding site, which suggests that the ability of females to accumulate resources for egg laying on the breeding site was an important determinant of laying times. At the population level, egg laying advanced by 1.15 days for every degree warmer on the breeding grounds. At the level of individua...

In several papers, it has been argued that two migratory species, the pied and the collared flycatcher, Ficedula hypoleuca and F. albicollis, take clutch size of a resident bird, the great tit Parus major, into account when deciding which of two adjacent nest boxes to use for their own breeding attempt (see Forsman et al. 2017). We termed this the interspecific cue hypothesis (the ICH; Slagsvold and Wiebe 2017) and argued that some of its basic assumptions have never been critically examined. Samplonius (2017) and Forsman et al. (2017) criticize our paper and argue that the ICH is the most plausible explanation but here we conclude that the new data they provide on the behaviour of the pied flycatcher (Forsman et al. 2017) are, in fact, inconsistent with the most critical assumption of the ICH. Therefore, the hypothesis should be rejected. This article is protected by copyright. All rights reserved.

Hatchlings use egg teeth to help break through the shell during hatching, but these structures could have an additional function of increasing nestlings' visibility. I investigated the size, color, and persistence of egg teeth in woodpeckers, which nest in dark cavities. Many species of woodpecker have two egg teeth, one each on the tip of the maxilla and of the mandible, which, together with the pale flanges, frame the open mouth when nestlings gape. A spectrometer confirmed that reflectance of Northern Flicker (Colaptes auratus) egg teeth is higher than that of the flanges across a wide range of wavelengths, reaching nearly 100% reflectance in the wavelengths most visible to woodpeckers. Reflectance of flanges peaked in the ultraviolet, which is less visible to woodpeckers. Therefore, parent woodpeckers can probably see egg teeth better than flanges. Within a brood, the brightness of egg teeth or flanges was not dependent on nestlings' size (hatching order), suggesting these structures are not...

The bright colours of nestlings' mouths are conspicuous when they beg. Three main hypotheses suggest that nestling mouth colour (1) increases detectability in dim ambient light, (2) signals health or quality, or (3) provides a means of offspring recognition. To distinguish these hypotheses, we manipulated both the flange colour (visual and UV spectrum) and the ambient light in the nest of three cavity-nesting species: a woodpecker and two passerines. Parents avoided nestlings with black-painted flanges to a greater extent in dim than in bright ambient light conditions, and the effect was most pronounced in the woodpecker, which had the deepest and darkest nest cavity of the three species studied. There was no difference in mass gain of nestlings with flanges painted white or yellow or with UV-block cream relative to controls, suggesting that neither UV reflectance nor carotenoid colour was a cue of nestling quality. These results support the detectability hypothesis and not the health-signalling or recognition function for bright flanges. Black-painted flycatcher nestlings were more disadvantaged in short trials ( 3 h), and we developed a model to explain how nonvisual components of begging, such as vocalizations or movements, may become more important than visual cues as nestlings become hungrier and beg more intensively over time. Our results suggest that bright flanges in cavity-nesting birds evolved primarily so that parents can locate offspring in dim light, but competition among nestlings may lead to exaggerated brightness. Furthermore, other components of begging such as movements or vocalizations may temporarily override a disadvantage of dull mouth colour.

To investigate the mating system of northern flickers (Colaptes auratus), we developed primers for 14 microsatellite loci and screened them in 68 unrelated adults and their offspring. All markers were highly polymorphic with 9 to +36 alleles per locus. One marker was Z-chromosome linked; one marker exceeded the size standard range and could not be analysed further. We checked the other 12 markers for Mendelian inheritance in 36 broods for which the social parents were known. Seven markers showed evidence for the presence of null alleles, and three of those showed significant deviation from Hardy-Weinberg equilibrium. Markers were generally unlinked.

Two subspecies of Northern Flicker (Colaptes auratus), Yellow-shafted Flicker (C. a. auratus) and Red-shafted Flicker (C. a. cafer), form a hybrid zone that stretches the length of North America and is apparently stable. The most widely accepted hypothesis for the zone, the “bounded-hybrid superiority” hypothesis, predicts that the fitness of hybrids should be equal to or higher than that of parental types within the hybrid zone. We compared the reproductive performance at various stages of the reproductive cycle among Northern Flickers of different phenotypes at a location in the hybrid zone in which individuals are predominantly reddish. Individuals with red and yellow coloring showed similar levels of aggression toward taxidermy models of pure Red-shafted and Yellow-shafted flickers, and there was no association between phenotype (color class) and the likelihood of winning agonistic contests. In addition, the color of the male and female parents was not related to nest initiation date, clutch...

It has been hypothesized that it is adaptive for birds to build new nests annually in order to avoid the accumulation of ectoparasites. Previous studies on costs of ectoparasitism have focused on cavity nesters in nestboxes while largely ignoring reproductive consequences in natural tree cavity nests, the context where nest selection strategies presumably evolved. To see whether ectoparasitism could be a driving selective force in the evolution of nest excavation in a woodpecker, I experimentally fumigated a subset of freshly excavated cavities and a subset of reused cavities of the northern flicker Colaptes auratus and compared reproductive performance with a set of control nests. The main ectoparasite of nestlings, a blood-sucking fly Carnus hemapterus, may have appeared one or two days earlier in reused nests but there was no difference between fresh and reused nests in intensities of flies one week post-hatching. Prevalence of parasitism reached 100% in both reused and freshly-excavated control nests in the second week. Nestlings from control nests had lower body mass residuals than those from fumigated nests after 15 d and fledged at a lower weight, suggesting that ectoparasitism by C. hemapterus was costly. However, fresh nest construction was no benefit, likely because the high dispersal ability of the ectoparasite meant all nests were colonized rapidly. Parents did not adjust provisioning effort according to parasitism as delivery rates did not differ between control and fumigated nests but delivery rates increased with brood size.