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Wing size and shape, expressed as wing loading and aspect ratio respectively, together with bill morphology are parameters that can reveal differences related to the foraging ecology of seabirds. Six species of booby (Sulidae) that inhabit the Pacific are the focus of this study: four mainly pelagic species, Masked Booby Sula dactylatra, Nazca Booby S. granti, Red-footed Booby S. sula, and Brown Booby S. leucogaster, and two coastal species, Blue-footed Booby S. nebouxii and Peruvian Booby S. variegata. Pelagic boobies showed segregation among species in body mass and relative bill size, and they differed in wing morphology (wing loading and aspect ratio) from the coastal boobies. The coastal Peruvian and Blue-footed Boobies are largely allopatric but overlap in northern Peru. In their area of sympatry, they showed evidence of character displacement in body size and in wing and bill morphology, which suggests that competition plays an important role in sympatry. This study improves our understanding of ecological interactions among Pacific boobies and of how selective pressures have shaped their ecomorphology and foraging behaviours. This article is protected by copyright. All rights reserved.

International audience; Understanding and modeling population change is urgently needed to predict effects of climate change on biodiversity. High trophic-level organisms are influenced by fluctuations of prey quality and abundance, which themselves may depend on climate oscillations. Modeling effects of such fluctuations is challenging because prey populations may vary with multiple climate oscillations occurring at different time scales. The analysis of a 28-yr time series of capture-recapture data of a tropical seabird, the Nazca Booby (Sula granti), in the Gal apagos, Ecuador, allowed us to test for demographic effects of two major ocean oscillations occurring at distinct timescales: the inter-annual El Ni~ no Southern Oscillation (ENSO) and inter-decadal oscillations. As expected for a tropical seabird, survival of fledgling birds was highly affected by extreme ENSO events; by contrast, neither recruitment nor breeding participation were affected by either ENSO or decadal oscillations. More interesting, adult survival, a demographic trait that canalizes response to environmental variations, was unaffected by inter-annual ENSO oscillations yet was shaped by the Pacific Decadal Oscillation and small pelagic fish regime. Adult survival decreased during oceanic conditions associated with higher breeding success, an association probably mediated in this species by costs of reproduction that reduce survival when breeding attempts end later. To our knowledge, this is the first study suggesting that survival of a vertebrate can be vulnerable to a natural multidecadal oscillation.

Yawning is a familiar and phylogenetically widespread phenomenon, but no consensus exists regarding its functional significance. We tested the hypothesis that yawning communicates to others a transition from a state of physiological and/or psychological arousal (for example, due to action of a stressor) to a more relaxed state. This arousal reduction hypothesis predicts little yawning during arousal and more yawning (above baseline) during and after down-regulation of arousal. Experimental capture-restraint tests with wild adult Nazca boobies (Sula granti), a seabird, increased yawning frequency after release from restraint, but yawning was almost absent during tests. Natural maltreatment by non-parental adults also increased yawning by nestlings, but only after the maltreatment ended and the adult left. CORT (corticosterone) was a logical a priori element of the stress response affecting the stressor-yawning relationship under the arousal reduction hypothesis, and cannot be excluded as such for adults in capture-restraint tests but is apparently unimportant for nestlings being maltreated by adults. The arousal reduction hypothesis unites formerly disparate results on yawning: its socially contagious nature in some taxa, its clear pharmacological connection to the stress response, and its temporal linkage to transitions in arousal between consciousness and sleep.

La Plata Island, Machalilla National Park, is located 30 km off the Ecuadorian coast. In June 2000, I surveyed the avifauna of La Plata Island. In total I observed 57 species of birds (25 families). At least 17 species are known to breed on the island; in fact, for mainland Ecuador, Waved Albatross Phoebastria irrorata, Red-billed Tropicbird Phaethon aethereus, Nazca Booby Sula granti, and Red-footed Booby Sula sula only breed in La Plata. Long-tailed Mockinbird subspecies Mimus longicaudatus platensis is the only endemic bird taxon of the island. House Sparrow Passer domesticus is the only non-native species of the island. Brown Booby Sula leucogaster, Ecuadorian Ground-Dove Columbina buckleyi, Little Woodstar Chaetocercus bombus and Yellow-bellied Elaenia Elaenia flavogaster are reported for the first time on the island. Isla de La Plata maintains an important biodiversity, and it is necessary to implement conservation, management and tourism plans on a sustainable way along with long-term monitoring studies of the fauna and flora.

The trophic ecology of Nazca Booby was evaluated through the analysis of gut contents collected between September 2004 and July 2005 during five field trips. From 110 induced regurgitation samples, the diet was analyzed using the variables number, weight and frequency of occurrence of the different nutritious categories, and using the distribution of the frequencies of sizes of preys at general, intraspecific and temporal levels. Oxyporrhamphus micropterus (halfbeaks fishes, family Hemiramphidae) and fishes of the family Exocoetidae (flying fishes) were the principal components found on the diet, followed by fishes of the families Carangidae and Escombridae. Variations were present in the consumption of the distinct categories at general, intraspecific and temporal levels, with the strongest differences in the consumption of preys of the family Hemiramphidae. The quantity of food taken by S. granti at Malpelo Island showed close relation with its reproductive cycle, and it adjusted to the model of energetic demand proposed for marine birds. Comparisons with other analogue studies showed slight differences between localities, apparently related with the availability of preys. It seems like there is a niche partition between females and males of S. granti at Malpelo Island related with the quantity and sizes of the preys ingested, and in a lesser degree with the composition of the diet. The present work is the first one to evaluate in detail the diet of the Nazca Booby and considerably extends the geographical range of this kind of studies in the Eastern Pacific.

The “cycle of violence” hypothesis implicates child abuse as a cause of later violent behavior via social transmission between generations. It has received mixed support from human research and has prompted the study of nonhuman models with comparable abuse behaviors. The underlying biology of child abuse remains a controversial subject, perhaps partly because in nonhuman animals similar behavior occurs relatively rarely in wild populations. The Nazca Booby (Sula granti), a colonial seabird, provides a nonhuman model in which maltreatment of nonfamilial young is widespread under normal living conditions. Essentially all adults show social attraction at some point in their lives to the offspring of other parents, often with a sexual and/or aggressive motivation. Here, we show a correlation between the degree to which a young bird is targeted by such adults and its own infliction of maltreatment later in life. The results provide the first evidence from a nonhuman of socially transmitted maltreatm...

We recorded 62 bird species on Clarion Island, Mexico (Revillagigedo Archipelago, Pacific Ocean) during 1998–2006, eight of which breed there, 52 are considered non-breeders, and breeding is likely but unconfirmed for the Red-billed Tropicbird (Phaethon aethereus), Nazca Booby (Sula granti), and an unidentified shearwater. Thirty species are new for the island. A census of the Clarion Burrowing Owl (Athene cunicularia rostrata) in 2002/03 suggested a maximum total population of ∼850 pairs. At least 46 pairs of Laysan Albatrosses (Phoebastria immutabilis) bred in 2002/03, but the species experienced total breeding failure during our study. This result was unexpected because feral pigs (Sus scrofa) were successfully eradicated from Clarion by 2002; endemic Clarion Ravens (Corvus corax clarionensis), an endemic snake (Clarion Racer, Masticophis anthonyi), and an unidentified ant were associated with egg and hatchling failures. A small colony of an unidentified shearwater could be a recolonization by...

Most of the known food webs are based on organic compounds provided by photoautotrophic organisms. The terrestrial ecosystem of Malpelo Island (Colombia) seems to be an exception, however, since it supports several trophic guilds without hosting an adequate amount of primary producers. It has been suggested that this apparent paradox might be explained by external inputs provided by seabirds, namely Nazca Boobies (Sula granti), forming a huge colony on Malpelo. This hypothesis has never been tested. Here, we present a first approach to quantify the significance of Nazca Booby inputs into the Malpelo ecosystem via excrement, second eggs/chicks (which are prone to die), and carcasses, respectively, during the major breeding season. The total input was calculated to amount to 171.6 t per breeding season, with excrements accounting for almost 99% (170 t) of this input. Second eggs/chicks contributed approximately 1.1 t (0.64%) and carcasses around 0.1 t (0.06%). These finding support the idea of the Nazca Booby facilitating a food chain that pairs the pelagic primary producers of the open ocean with the terrestrial consumers of an island. Species most strongly profiting from this process include three endemic lizard species (Anolis agassizi, Diploglossus millepunctatus, Phyllodactylus transversalis) and the land crab (Johngarthia malpilensis).

The formation and dissolution of mating pair bonds have been fruitful areas of investigation for evolutionary biologists. Adaptive mate choice has been the focus of most research on pair dissolution. However, recent work has shown that an important cause of pair dissolution can be involuntary forced divorce, where intruder(s) oust one or both partners. Previously, we presented evidence that, in a male-biased population, females exchanged a reproductively depleted male for a new ‘refreshed’ mate. This ‘mate rotation’ model of divorce could be driven by female choice, forced divorce by unpaired males, or by males forgoing reproduction to recover condition. Here, we examine these alternatives with behavioural and demographic data from our long-term study of banded Nazca boobies. The mate rotation pattern of divorce appears to be driven by a combination of two circumstances involving a female’s abandonment of a previous partnership. In some cases, the female appeared to cooperate with a male intruder, causing her former partner to leave the nest. In other cases, the female abandoned her former mate and joined a new male at another nest site. Recent studies that have disentangled age and breeding experience from pair bond length have shown that an initial increase in reproductive output correlated with pair bond length, but after a period of time together the reproductive success of the pair declined. Given the assumed ubiquity of the cost of reproduction, divorce after a lengthy pair bond would seem to be advantageous for one or both mates when fresh potential partners are available.

The evolution of longevity requires that the marginal investment in self-maintenance at the expense of reproductive effort is favored by realizing a longer reproductive lifespan. This can occur when extrinsic mortality factors (weather, predators, etc.) are less important than intrinsic mortality factors, such as the physiological cost of reproduction. Long-lived pelagic seabirds have low annual reproductive output and prolonged offspring growth periods that are thought to have evolved to accommodate marine resource variability. The life-history theory of senescence predicts that these same taxa should minimize per diem reproductive costs and shift effects of resource variability to the offspring. To address this prediction, we measured parental effort, offspring growth, and one aspect of self-maintenance (serum immunoglobulin G concentration [IgG]) in a long-lived pelagic seabird, the Nazca Booby (Sula granti). We collected data on 38 families in the 2002–2003 breeding season on Isla Espanola, G...

Biased operational sex ratios (OSRs) can drive sexual selection on members of the over-represented sex via competition for mates, causing higher variance and skew in reproductive success (RS) among them if an individual's quality is a persistent characteristic. Alternatively, costs of reproduction may degrade breeding performance, creating the opportunity for members of the limiting sex to switch mates adaptively, effectively homogenizing variance and skew in RS among the sex in excess. We tested these two contrasting models in a male-biased population of the Nazca booby ( Sula granti ) with demonstrated costs of reproduction with data on total RS over a 14-year period. Variances and skews in RS were similar, and males changed from breeder to non-breeder more frequently than females. Under the persistent individual quality model, females should mate only with high quality males, and non-breeding males should seldom enter the breeding pool, yet 45% of non-breeding males (re)entered the breeding pool each year on average. Many Nazca booby females apparently exchange a depleted male for a new mate from the pool of current non-breeder males. Our evidence linking serial monogamy to costs of reproduction is novel and suggests selection on female mating preferences based on an interaction between at least two life-history components (OSR and reproductive effort).

Knowledge of the ontogeny of the sex ratio is required for proper framing of evolutionary hypotheses regarding adaptive parental sex allocation, competition for mates, evolution of mating systems, and endangered species management. We traced the development of a male-biased adult sex ratio in Nazca Boobies (Sula granti) by determination of the sex ratio at hatching, fledging, and at returning to join the adult population. The sex ratio at hatching and fledging did not differ from unity, while the return sex ratio was significantly male-biased. Therefore, the observed adult sex ratio bias arises after the period of parental care ends, during the subadult/juvenile stage, with important implications for mate competition.

Nazca Booby (Sula granti) broods in the Galapagos Islands showed 0% extra-pair fertilization, based on multilocus band-sharing values. The 95% CI of this estimate for all chicks was 0–0.098, and for all broods it was 0–0.139. These are the first data on extra-pair paternity to be reported for a member of the family Sulidae.

We documented natal and breeding dispersal at several spatial scales by Galapagos Nazca boobies Sula granti, a wide-ranging pelagic seabird. We found exceptionally low degrees of both types of dispersal despite these birds’ vagility. Median natal dispersal distances were 26 m and 105 m for males and females, respectively. Median breeding dispersal distances for both sexes were 0 m. No natal or breeding dispersals occurred from our study site at Punta Cevallos, Isla Espanola to six other colonies in the Galapagos, but we did document four long-distance natal dispersals from Punta Cevallos to islands near the South American coast. Recaptures and dead recoveries of ringed birds showed long distance non-breeding movements to the Central American coast and elsewhere in the eastern Pacific, contrasting with the very limited dispersal to breeding sites.

Adult Nazca boobies (Sula granti) show an unusual interest in both conspecific and congeneric nestlings, visiting them at their nest sites and performing mixtures of affiliative, aggressive, and sexual behaviours. Using a 20 year database from a large Nazca booby colony on Isla Española, Galápagos Islands, Ecuador, we describe the behaviour and the individuals performing the behaviour. Non-parental Adult Visitors ('NAVs') are typically 'unemployed' (non-breeding birds or recently failed breeders), and make visits of 1-60 min to unguarded chicks. Males and females are equally likely to exhibit the behaviour, if they are unemployed; since most unemployed birds are male, due to a sex ratio bias, most NAVs are male. Very young chicks and chicks nearing fledging are not visited, because young chicks are always attended by protective parents, and old chicks can defend themselves. When acting affiliatively, NAVs may simply stand by the chick, or may preen it and present gifts of pebbles and feathers. Aggression by the NAV often leaves scratches on the chick's body, but seldom causes the chick's death directly. However, landbirds take blood-meals from the scratches during food shortages, deepening the wound and eventually killing the chick. The least common NAV behaviour is sexual, in which adults perform male copulatory behaviour with the chick. Sexual behaviour occurs in 14.3% of visits by males, and 6.8% of visits by females. NAV behaviour is the direct or indirect cause of mortality of up to 24.6% of chicks, representing up to 41.6% of all deaths, in a given year. Approximately 80% of non-breeding birds in a given year show NAV behaviour, and since most adults are non-breeders at some point in life, most adults show NAV behaviour at some point. We propose a number of hypotheses to explain the causation of this puzzling and ecologically important behaviour.

Incubation in most avian species involves transferring heat from parent to egg through a highly vascularized brood patch. Some birds, however, do not develop a brood patch. Unusual among birds, these species hold their eggs under the webs of their feet, but the role of the feet in heat transfer is uncertain. Often the webs are positioned between the feathered abdomen and the egg during incubation, suggesting that either the abdomen, the feet, or both could transfer heat to the egg. We studied heat transfer from foot webs to eggs during incubation in Nazca boobies by spatially separating the feet from the abdomen using an oversized egg. We found that feet transfer heat to eggs independently of any heat that may be transferred from the abdomen. In addition, we found that incubating boobies had significantly greater vascularization in their foot webs, measured as a percentage of web area covered by vessels, than nonincubating boobies. We also found that males, whether incubating or nonincubating, had significantly less web vascularization than females. We concluded that vascularized Nazca booby feet function in the same way during incubation that vascularized brood patches do, acting as surrogate brood patches.

Blue-footed boobies (Sula nebouxii) in the Galápagos Islands nest at coastal sites such as cliff edges if Nazca boobies (S. granti) are absent. However, if sympatric with nesting Nazca boobies, they nest nearby, but farther inland, in areas with little topographical relief. Nazca boobies nest at the coastal sites whether blue-footed boobies are present or not. The segregated nesting pattern of these two species offers a model system to investigate factors influencing community structure. We tested a non-interactive hypothesis, in which different fundamental niches generate the non-overlapping distributions, and an interactive hypothesis, in which the two fundamental niches overlap and an interaction between the two species causes the segregation. Data on three factors considered as likely parameters differentiating fundamental niches (nest microclimate, nature of the nesting substrate, and ease of taking flight from nest sites) failed to support the non-interactive hypothesis. These results suggest that the two species have indistinguishable fundamental niches with respect to these parameters, but different realized niches. Researchers studying resource partitioning by ecologically similar species often only consider competition (a "-/-" interaction) to explain situations like this, ignoring the more parsimonious amensal (0/-) possibility. Nesting segregation in this situation is apparently caused by attacks of non-breeding adult Nazca boobies on blue-footed booby nestlings, injuring nestlings and ultimately preventing them from fledging. The interaction does not result in any discernible costs or benefits (i.e., effects on fecundity or survival) for the adult Nazca boobies, so it is best described as an amensal interaction. This interaction provides a sufficient explanation of the observed nesting segregation, and precludes present competition for nesting space.

We reviewed the status of the breeding marine birds on San Benedicto Island, Mexico, based on >100 years of published observations and seven of our own surveys conducted between 1978 and 2000. We found that there have been marked changes in the island avifauna with two main trends evident. First, a volcanic eruption destroyed much of the island in 1952. The Wedge-tailed Shearwater (Puffinus pacificus; estimated breeding population 1,000 pairs), Townsend's Shearwater (Puffinus auricularis; probable breeder, small numbers), and Red-footed Booby (Sula sula; 60 pairs) historically had much larger populations, but they apparently never fully recovered from the eruption. The Masked Booby (Sula dactylatra; 2,185 pairs), however, has become much more abundant perhaps due to changes in the vegetation. The second trend is that within the last three decades at least two, and possibly four, species from the central Pacific have colonized the island. The Laysan Albatross (Phoebastria immutabilis; 12 pairs) started breeding in the late 1980s; Black-footed Albatross (Phoebastria nigripes; 1 pair) in 2000. Red-tailed Tropicbirds (Phaethon rubricauda; probable breeder, 10 pairs) may have started breeding in the 1980s, and at least some of the breeding Brown Boobies (Sula leucogaster; 300 pairs) are from central Pacific populations. The reason(s) for this influx of central Pacific species is unknown, but likely involves changes in the marine environment. Other breeding species include the Red-billed Tropicbird (Phaethon aethereus; 200 pairs), Nazca Booby (Sula granti; 50 pairs), Great Frigatebird (Fregata minor; 165 pairs), and Magnificent Frigatebird (Fregata magnificens; 5 pairs).

In obligately siblicidal bird species, aggressive behavior by a dominant chick results in a fixed brood size of one, yet these species usually show clutch size variation between individuals. Simmons proposed that variation in clutch size in obligately siblicidal species is related to a trade-off between egg quality and egg quantity: some individuals produce a single highly hatchable egg, while others produce two small, lower quality eggs. We tested the egg quality hypothesis as an explanation for observed clutch size variation in the Nazca booby (Sula granti), an obligately siblicidal seabird. We tested the assumption that egg volume is positively correlated with hatchability and the prediction that eggs from one-egg clutches are larger than eggs from two-egg clutches. We did not find a positive relationship between egg volume and hatchability in this species. Eggs from two-egg clutches were either equivalent in volume or larger than eggs from one-egg clutches. Thus, the egg quality hypothesis was rejected as an explanation for clutch size variation in the Nazca booby. Instead, two-egg clutches appear to be favored because of the insurance value of the second-laid egg, while one-egg clutches result from food limitation. Copyright 2002.

In this paper we describe the ectoparasitic lice (Insecta: Phthiraptera) found on 5 species of seabirds (magnificent frigatebird Fregata magnificens; great frigatebird Fregata minor; Nazca booby Sula granti; blue-footed booby Sula nebouxii; and red-footed booby Sula sula) on the Galapagos Archipelago. We found 9 species of ectoparasitic lice: 5 species of Pectinopygus ischnocerans, 1 infesting each host; 2 species of Colpocephalum amblyceran lice, 1 on each frigatebird species; and 2 shared amblycerans, Eidmanniella albescens (Piaget, 1880) found on Nazca and blue-footed boobies and Fregatiella aurifasciata (Kellogg, 1899) found on the 2 frigatebirds. We tested the relative importance and interactions of host sex, body size, host, island, host family, and breeding status and found that inter-island differences were the main predictors of prevalence and infestation intensity. These differences could be related to host density or weather, but further evidence is needed.

Summary 1 Natural selection is expected to optimize clutch size, but intrapopulation variation is maintained in many bird species. The Nazca booby provides a simple system in which to investigate clutch size evolution because clutch size and brood size are decoupled due to obligate siblicide. The indirect effect of brood size on clutch size evolution can therefore be eliminated. 2 In Nazca boobies, second eggs provide insurance against the failure of the first egg or early death of the first hatchling, but approximately half of all females lay only one egg. We tested the hypothesis that one-egg clutches result from food limitation by providing female Nazca boobies with supplemental food. 3 A higher proportion of supplemented females produced two-egg clutches than did control females. Supplemented females produced larger second-laid eggs than did control females, but not first-laid eggs. Laying date and laying interval were not affected. 4 Comparisons of clutch size and egg volume between years indicated that the supplemental feeding experiment was not conducted in a year with a poor natural food supply. Thus supplemented females produced larger clutch sizes despite apparently normal natural food levels. 5 This experiment nearly completes our understanding of clutch size variation in the Nazca booby, and indicates that food limitation and the costs of egg-laying should be considered carefully in studies of clutch size evolution.

A variety of organisms regularly produce more offspring than they raise. Despite the apparent energetic waste of such a reproductive tactic, overproduction may be favored by natural selection in some cases. One such case is when surplus offspring can serve as replacements, or insurance, for failed siblings. We tested the Insurance Egg Hypothesis (IEH) as an explanation for the overproduction of offspring in an obligately siblicidal seabird, the Nazca booby (Sula granti), which fledges a maximum of one nestling regardless of its clutch size. We manipulated clutch sizes within the range of natural variation encountered in this species (one–two eggs). The IEH predicts that parents with two-egg clutches should have higher reproductive success than those with one-egg clutches because the second egg can provide a nestling when the first egg fails to hatch, or when the first chick dies young. Consistent with the IEH, natural one-egg clutches that were enlarged to two eggs produced more hatchlings and fledglings than control one-egg clutches did, and natural two-egg clutches that were reduced to one egg produced fewer hatchlings and fledglings than control two-egg clutches did. We also evaluated aspects of the Individual Optimization Hypothesis, which proposes that individual optimal clutch sizes differ, as an explanation for clutch size variation in this species. In Nazca boobies, selection driven by replacement value appears to favor clutches larger than one even though final brood size is invariably one. One-egg clutches may be produced by parents experiencing some proximate limitation, such as a lack of food. Key words: clutch size, Individual Optimization Hypothesis, Insurance Egg Hypothesis, Nazca booby, siblicide, Sula granti, surplus offspring. [Behav Ecol 12:340–347 (2001)]

Seabirds are considered highly mobile, able to fly great distances with few apparent barriers to dispersal. However, it is often the case that seabird populations exhibit strong population genetic structure despite their potential vagility. Here we show that Galapagos Nazca booby (Sula granti) populations are substantially differentiated, even within the small geographic scale of this archipelago. On the other hand, Galapagos great frigatebird (Fregata minor) populations do not show any genetic structure. We characterized the genetic differentiation by sampling five colonies of both species in the Galapagos archipelago and analyzing eight microsatellite loci and three mitochondrial genes. Using an F-statistic approach on the multilocus data, we found significant differentiation between nearly all island pairs of Nazca booby populations and a Bayesian clustering analysis provided support for three distinct genetic clusters. Mitochondrial DNA showed less differentiation of Nazca booby colonies; only Nazca boobies from the island of Darwin were significantly differentiated from individuals throughout the rest of the archipelago. Great frigatebird populations showed little to no evidence for genetic differentiation at the same scale. Only two island pairs (Darwin - Wolf, N. Seymour - Wolf) were significantly differentiated using the multilocus data, and only two island pairs had statistically significant φ(ST) values (N. Seymour - Darwin, N. Seymour - Wolf) according to the mitochondrial data. There was no significant pattern of isolation by distance for either species calculated using both markers. Seven of the ten Nazca booby migration rates calculated between island pairs were in the south or southeast to north or northwest direction. The population differentiation found among Galapagos Nazca booby colonies, but not great frigatebird colonies, is most likely due to differences in natal and breeding philopatry.

Non-breeding Nazca booby adults exhibit an unusual and intense social attraction to non-familial conspecific nestlings. Non-parental Adult Visitors (NAVs) seek out and approach unguarded nestlings during daylight hours and display parental, aggressive, and/or sexual behavior. In a striking parallel to the "cycle of violence" of human biology, degree of victimization as a nestling is strongly correlated with frequency of future maltreatment behavior exhibited as an adult. Here, we investigate candidates for permanent organization of this behavior, including immediate and long-term changes in growth and circulating corticosterone and testosterone due to victimization, by protecting some nestlings with portable exclosures that prevented NAV visits and comparing them to controls. During maltreatment episodes, nestlings experience an approximately five-fold increase in corticosterone concentration, and corticosterone remains elevated approximately 2.8-fold until at least the following morning. Our results are consistent with the possibility that repeated activation of the hypothalamic-pituitary-adrenal axis permanently organizes future adult maltreatment behavior. No effect on growth, acute or chronic changes in testosterone, or chronic corticosterone elevation was detected or appeared to be components of an organizational effect. This unusual behavior presents an opportunity to investigate neural, endocrine, and behavioral organization resulting from early social trauma that may be conserved across vertebrate classes.

Background Exposure to androgens early in development, while activating adaptive aggressive behavior, may also exert long-lasting effects on non-target components of phenotype. Here we compare these organizational effects of perinatal androgens in closely related Nazca (Sula granti) and blue-footed (S. nebouxii) boobies that differ in neonatal social system. The older of two Nazca booby hatchlings unconditionally attacks and ejects the younger from the nest within days of hatching, while blue-footed booby neonates lack lethal aggression. Both Nazca booby chicks facultatively upregulate testosterone (T) during fights, motivating the prediction that baseline androgen levels differ between obligately siblicidal and other species. Methodology/Principal Findings We show that obligately siblicidal Nazca boobies hatch with higher circulating androgen levels than do facultatively siblicidal blue-footed boobies, providing comparative evidence of the role of androgens in sociality. Although androgens confer a short-term benefit of increased aggression to Nazca booby neonates, exposure to elevated androgen levels during this sensitive period in development can also induce long-term organizational effects on behavior or morphology. Adult Nazca boobies show evidence of organizational effects of early androgen exposure in aberrant adult behavior: they visit unattended non-familial chicks in the colony and direct mixtures of aggression, affiliative, and sexual behavior toward them. In a longitudinal analysis, we found that the most active Non-parental Adult Visitors (NAVs) were those with a history of siblicidal behavior as a neonate, suggesting that the tendency to show social interest in chicks is programmed, in part, by the high perinatal androgens associated with obligate siblicide. Data from closely related blue-footed boobies provide comparative support for this interpretation. Lacking obligate siblicide, they hatch with a corresponding low androgen level, and blue-footed booby adults show a much lower frequency of NAV behavior and a lower probability of behaving aggressively during NAV interactions. This species difference in adult social behavior appears to have roots in both pleiotropic and experiential effects of nestling social system. Conclusions/Significance Our results indicate that Nazca boobies experience life-long consequences of androgenic preparation for an early battle to the death.

The red-footed booby (Sula sula) is considered one of the most polymorphic seabirds, with 3 recognized major adult plumage types: 1) white, 2) white-tailed brown, and 3) brown and several degrees of intermediates. Here we show that the white/melanic polymorphism observed in this species is perfectly associated with 2 point substitutions, Val85Met and His207Arg, at the melanocortin-1 receptor (MC1R) gene. Among the melanic plumage variants, we also found a strong association between the degree of melanism and the number of copies of variant MC1R alleles. Furthermore, the Val85Met point substitution has been previously shown to be associated with melanic phenotypes in the lesser snow goose (Anser c. caerulescens), suggesting parallel evolution of the melanic allele, and hence, melanism, between these 2 distantly related species. We also compared the MC1R locus in red-footed boobies with a nonpolymorphic congener, the Nazca booby (Sula granti), in which all adults are white. We found that Nazca boobies present the same genotype at sites 85 and 207 as white morph red-footed boobies.

While obligate siblicide is a phylogenetically widespread behavior, known from plants, insects, birds, and other taxa, with important implications for life history evolution, comprehensive evaluations of its costs and benefits to parents are rare. We used 12 years of breeding and band resight data to evaluate the importance of several potential benefits that marginal offspring (the usual victims of obligate siblicide) could provide to parent Nazca boobies (Sula granti), a seabird. We found no evidence for the resource-tracking hypothesis: 99.95% of two-chick broods were reduced to one chick before fledging, and the single exceptional brood probably lost one chick between fledging and independence. Behavioral observations indicated that siblicidal aggression caused most mortality of marginal chicks, and at least contributed to the remainder. We also found no evidence that marginal offspring provide a food resource for other family members. Marginal chicks benefit parents via adoption into other families, and possibly also in the context of progeny choice, but these benefits are minor compared to the insurance that marginal chicks provide against early failure of core (first-hatched) offspring. Further evaluation of the Insurance Egg Hypothesis showed that marginal and core offspring are functionally equivalent in the absence of sibling interactions, and that core offspring incur no detectable costs from behaving siblicidally. Nazca boobies are truly obligate brood reducers, with parents receiving principally insurance benefits from marginal offspring, but many birds and other taxa exhibiting persistent, unconditional sibling aggression do not exhibit universal brood reduction. Insurance is only one of several potential benefits that marginal offspring can confer on parents, and a multi-hypothesis approach to decompose the different types of benefits is required to understand the evolution of clutch size in other obligately siblicidal species.

We investigated the effects of moon phases and age on diel rhythms of plasma melatonin and corticosterone in free-living Nazca boobies (Sula granti) on the Galapagos Islands, Ecuador. Melatonin and corticosterone secretion are regulated by the circadian system and the two hormones play a role in the control of locomotor activity and foraging, which can be influenced by moon phases. These seabirds have a long life span and in many vertebrates circadian function deteriorates with age. The functioning of the circadian system under different environmental conditions and changes related to age are poorly understood and hardly studied in wild birds. Nazca boobies had generally low plasma melatonin concentrations but showed a diel variation with higher concentrations at 00:00 and 16:00h. The diel variations in melatonin concentrations disappeared during full moon, suggesting that natural light levels at night can suppress melatonin secretion in Nazca boobies. Maximal melatonin concentrations tended to decline in older birds (10-19 years). Birds showed a clear diel variation in basal plasma corticosterone with a peak in the early morning, before the active period begins, and low concentrations throughout the day. As with melatonin, there were no diel variations in corticosterone at full moon, which may be due to different activity patterns in response to food availability or changes in the circadian system. While other studies have found a relationship between corticosterone and melatonin, we found no such correlation in Nazca boobies. The lunar cycle appears to affect the hormone titers of Nazca boobies both directly and indirectly. First, melatonin rhythms can be directly affected by the light intensity associated with full moon. Second, prey availability may change foraging patterns and can therefore indirectly alter corticosterone secretion in Nazca boobies.

Pitman and Jehl (1998) recently argued that Masked Boobies (formerly Sula dactylatra granti) breeding on the Nazca Plate in the eastern Pacific Ocean are morphologically and ecologically distinct from other Masked Boobies and may represent a full species. The American Ornithologists' Union subsequently elevated that subspecies to a full species: the Nazca Booby (S. granti). To evaluate that change in classification, we compared sequence variation in the mitochondrial cytochrome-b gene among 75 Nazca Boobies and 37 Masked Boobies representing three subspecies from the central and eastern Pacific and Atlantic oceans. Results indicated strong differentiation of cytochrome-b variation among taxa. Sequences constituted three distinct groups: Nazca Boobies, Masked Boobies from the central and eastern Pacific (S. d. personata and S. d. californica), and Masked Boobies (S. d. dactylatra) from the Caribbean and Atlantic. Those three groups probably diverged within a very short period, 400,000–500,000 year...