Allele frequency dynamics under sex-biased demography and sex-specific inheritance in a pedigreed jay population.

Sex-biased demography, including sex-biased survival or migration, can alter allele frequency changes across the genome. In particular, we can expect different patterns of genetic variation on autosomes and sex chromosomes due to sex-specific differences in life histories, as well as differences in effective population size, transmission modes, and the strength and mode of selection. Here, we demonstrate the role that sex differences in life history played in shaping short-term evolutionary dynamics across the genome. We used a 25-year pedigree and genomic dataset from a long-studied population of Florida Scrub-Jays (Aphelocoma coerulescens) to directly characterize the relative roles of sex-biased demography and inheritance in shaping genome-wide allele frequency trajectories. We used gene dropping simulations to estimate individual genetic contributions to future generations and to model drift and immigration on the known pedigree. We quantified differential expected genetic contributions of males and females over time, showing the impact of sex-biased dispersal in a monogamous system. Due to female-biased dispersal, more autosomal variation is introduced by female immigrants. However, due to male-biased transmission, more Z variation is introduced by male immigrants. Finally, we partitioned the proportion of variance in allele frequency change through time due to male and female contributions. Overall, most allele frequency change is due to variance in survival and births. Males and females make similar contributions to autosomal allele frequency change, but males make higher contributions to allele frequency change on the Z chromosome. Our work shows the importance of understanding sex-specific demographic processes in characterizing genome-wide allele frequency change in wild populations.

Impacts of increasing isolation and environmental variation on Florida Scrub-Jay demography.

Isolation caused by anthropogenic habitat fragmentation can destabilize populations. Populations relying on the inflow of immigrants can face reduced fitness due to inbreeding depression as fewer new individuals arrive. Empirical studies of the demographic consequences of isolation are critical to understand how populations persist through changing conditions. We used a 34-year demographic and environmental dataset from a population of cooperatively-breeding Florida Scrub-Jays ( Aphelocoma coerulescens ) to create mechanistic models linking environmental and demographic factors to population growth rates. We found that the population has not declined despite both declining immigration and increasing inbreeding, owing to a coinciding response in breeder survival. We find evidence of density-dependent immigration, breeder survival, and fecundity, indicating that interactions between vital rates and local density play a role in buffering the population against change. Our study elucidates the impacts of isolation on demography and how long-term stability is maintained via demographic responses.

Visual Monitoring Strategies of Sentinels in a Cooperative Breeder.

Vigilance is important for early detection of threats. Previous studies have focused on the allocation of time to vigilance but neglected how animals monitor their surroundings during vigilance. Where animals look and how long each look lasts can affect the quality of visual monitoring and thus the ability to detect threats during vigilance. We examined visual monitoring strategies in the Florida scrub-jay (Aphelocoma coerulescens), a cooperative breeder with sentinel behaviour. Sentinels in this species make head turns from vantage points to detect the arrival of predators and intruding neighbours. We found that sentinels initiated head turns at regular intervals and also returned their gaze to areas previously monitored at regular intervals, which is predicted when predators and intruders rely on surprise rather than stealth to approach. Sentinels made head turns in several directions, but often more frequently on one side of the body than the other, which was not predicted for regular vigilance. Average look duration during sentinel bouts was shorter in smaller groups and in juveniles. We argue that shorter looks are beneficial to increase visual coverage in more threatening situations. Our study highlights how visual monitoring strategies during vigilance reflect the risk posed by predators and intruders.

Dynamics of reduced genetic diversity in increasingly fragmented populations of Florida scrub jays,Aphelocoma coerulescens.

Understanding the genomic consequences of population decline is important for predicting species' vulnerability to intensifying global change. Empirical information about genomic changes in populations in the early stages of decline, especially for those still experiencing immigration, remains scarce. We used 7834 autosomal SNPs and demographic data for 288 Florida scrub jays (Aphelocoma coerulescens; FSJ) sampled in 2000 and 2008 to compare levels of genetic diversity, inbreeding, relatedness, and lengths of runs of homozygosity (ROH) between two subpopulations within dispersal distance of one another but have experienced contrasting demographic trajectories. At Archbold Biological Station (ABS), the FSJ population has been stable because of consistent habitat protection and management, while at nearby Placid Lakes Estates (PLE), the population declined precipitously due to suburban development. By the onset of our sampling in 2000, birds in PLE were already less heterozygous, more inbred, and on average more related than birds in ABS. No significant changes occurred in heterozygosity or inbreeding across the 8-year sampling interval, but average relatedness among individuals decreased in PLE, thus by 2008 average relatedness did not differ between sites. PLE harbored a similar proportion of short ROH but a greater proportion of long ROH than ABS, suggesting one continuous population of shared demographic history in the past, which is now experiencing more recent inbreeding. These results broadly uphold the predictions of simple population genetic models based on inferred effective population sizes and rates of immigration. Our study highlights how, in just a few generations, formerly continuous populations can diverge in heterozygosity and levels of inbreeding with severe local population decline despite ongoing gene flow.

Staging to join non-kin groups in a classical cooperative breeder, the Florida scrub-jay.

Why unrelated members form groups in animal societies remains a pertinent topic in evolutionary biology because benefits for group members often are not obvious. We studied subordinates that disperse to join unrelated social groups in the Florida scrub-jay Aphelocoma coerulescens, a cooperative breeding species mainly composed of kin-based groups. We evaluated potential adaptive benefits of dispersing to become an unrelated helper (staging) versus remaining home and dispersing only to pair and breed (direct dispersal) to understand why non-kin-based groups form. Using 35 years of demographic data, we quantified life-history aspects of staging individuals and tested associations between social and ecological factors on the natal and staging territories. We compared fitness outcomes between dispersal strategies by analysing survival, breeding recruitment and direct reproductive output. We tested for sexual asymmetry potentially driven by differences in territory acquisition patterns and female-biased dispersal for this species. Of birds that reached 1 year, 28% staged at a non-natal territory before breeding or disappearing. Staging dispersers departed at younger ages and moved greater distances than direct dispersers. When looking at proximate factors on the natal territory associated with staging, males left groups with many same-sex helpers, while females often left when their father disappeared. For both sexes, staging individuals more likely came from high-quality territories and joined groups with fewer same-sex helpers than in their natal group. While staging and direct dispersers did not differ in survival or likelihood of becoming a breeder, staging males became breeders later and had lower lifetime reproductive success than direct dispersers. In Florida scrub-jays, staging appears to be an alternative strategy for female helpers, but a best-of-a-bad-situation for males. This sexual asymmetry is consistent with males having more options than females to achieve higher reproductive success by breeding near home. Trade-offs in cost-benefits of departing the natal territory and joining unrelated groups as a helper seem to best explain alternative dispersal patterns, with optimal social queues primarily driving the benefits. This research highlights plasticity in dispersal behaviour in response to social and environmental conditions and offers a new perspective in our understanding of non-kin-based social groups.

Fire history and weather interact to determine extent and synchrony of mast-seeding in rhizomatous scrub oaks of Florida.

In disturbance-prone ecosystems, fitness consequences of plant reproductive strategies are often determined by the relative timing of seed production and disturbance events, but the role of disturbances as proximate drivers of seed production has been overlooked. We use long-term data on seed production in Quercus chapmanii, Q. geminata and Q. inopina, rhizomatous oaks found in south central Florida's oak scrub, to investigate the role of fire history and its interaction with weather in shaping acorn production and its synchrony. Acorn production increased with the time since last fire, combined with additive or interactive effects of spring precipitation (+) or drought (-). Furthermore, multiple matrix regression models revealed that ramet pairs with shared fire history were more synchronous in seed production than ones that burned in different years. Long-term trends suggest that increasingly drier spring weather, in interaction with fire frequency, may drive a decline of seed production. Such declines could affect the community of acorn-reliant vertebrates in the Florida scrub, including endangered Florida scrub-jays (Aphelocoma coerulescens). These results illustrate that fire can function as a proximate driver of seed production in mast-seeding species, highlighting the increasingly recognized importance of interactions among reproductive strategies and disturbance regimes in structuring plant populations and communities. This article is part of the theme issue 'The ecology and evolution of synchronized seed production in plants'.

Life history stage explains behavior in a social network before and during the early breeding season in a cooperatively breeding bird.

In species with stage-structured populations selection pressures may vary between different life history stages and result in stage-specific behaviors. We use life history stage to explain variation in the pre and early breeding season social behavior of a cooperatively breeding bird, the Florida scrub-jay (Aphelocoma coerulescens) using social network analysis. Life history stage explains much of the variation we observed in social network position. These differences are consistent with nearly 50 years of natural history observations and generally conform to a priori predictions about how individuals in different stages should behave to maximize their individual fitness. Where the results from the social network analysis differ from the a priori predictions suggest that social interactions between members of different groups are more important for breeders than previously thought. Our results emphasize the importance of accounting for life history stage in studies of individual social behavior.

Allele frequency dynamics in a pedigreed natural population.

A central goal of population genetics is to understand how genetic drift, natural selection, and gene flow shape allele frequencies through time. However, the actual processes underlying these changes-variation in individual survival, reproductive success, and movement-are often difficult to quantify. Fully understanding these processes requires the population pedigree, the set of relationships among all individuals in the population through time. Here, we use extensive pedigree and genomic information from a long-studied natural population of Florida Scrub-Jays (Aphelocoma coerulescens) to directly characterize the relative roles of different evolutionary processes in shaping patterns of genetic variation through time. We performed gene dropping simulations to estimate individual genetic contributions to the population and model drift on the known pedigree. We found that observed allele frequency changes are generally well predicted by accounting for the different genetic contributions of founders. Our results show that the genetic contribution of recent immigrants is substantial, with some large allele frequency shifts that otherwise may have been attributed to selection actually due to gene flow. We identified a few SNPs under directional short-term selection after appropriately accounting for gene flow. Using models that account for changes in population size, we partitioned the proportion of variance in allele frequency change through time. Observed allele frequency changes are primarily due to variation in survival and reproductive success, with gene flow making a smaller contribution. This study provides one of the most complete descriptions of short-term evolutionary change in allele frequencies in a natural population to date.

Mass fluctuation in breeding females, males, and helpers of the Florida scrub-jay Aphelocoma coerulescens.

Much evidence suggests that birds actively regulate their body mass reserves relative to their energy needs. Energy requirements during reproduction may differ in relation to sex-specific behavioural roles or, in the case of cooperative breeders, breeders relative to helpers. We measured body mass of free-living Florida scrub-jays throughout the nesting season by training them to land on an electronic balance. Jays exhibited a pattern of diurnal linear mass gain, from morning to afternoon. Day-to-day mass fluctuations, defined as the difference between mass on two consecutive days, were small (>80% were within 2 g, less than 3% of the mass of an adult bird) for all classes of jays: female breeders, male breeders and prebreeding helpers. The jays, which live in subtropical south-central Florida, did not exhibit changes in day-to-day mass fluctuation relative to weather or climate variables or calendar date. Day-to-day mass fluctuations influenced mass fluctuation between the following third and fourth days. These changes were usually compensatory, indicating that jays are able to regulate their body mass on a short-term basis, despite strong differences in their roles in reproduction. During reproduction, jays have a relatively predictable and abundant food supply, thus the appropriate strategy may be to maintain a stable body mass that balances some energy reserves against maintaining a low body mass for efficient flight, as required during reproduction.

Deconstructing isolation-by-distance: The genomic consequences of limited dispersal.

Geographically limited dispersal can shape genetic population structure and result in a correlation between genetic and geographic distance, commonly called isolation-by-distance. Despite the prevalence of isolation-by-distance in nature, to date few studies have empirically demonstrated the processes that generate this pattern, largely because few populations have direct measures of individual dispersal and pedigree information. Intensive, long-term demographic studies and exhaustive genomic surveys in the Florida Scrub-Jay (Aphelocoma coerulescens) provide an excellent opportunity to investigate the influence of dispersal on genetic structure. Here, we used a panel of genome-wide SNPs and extensive pedigree information to explore the role of limited dispersal in shaping patterns of isolation-by-distance in both sexes, and at an exceedingly fine spatial scale (within ~10 km). Isolation-by-distance patterns were stronger in male-male and male-female comparisons than in female-female comparisons, consistent with observed differences in dispersal propensity between the sexes. Using the pedigree, we demonstrated how various genealogical relationships contribute to fine-scale isolation-by-distance. Simulations using field-observed distributions of male and female natal dispersal distances showed good agreement with the distribution of geographic distances between breeding individuals of different pedigree relationship classes. Furthermore, we built coalescent simulations parameterized by the observed dispersal curve, population density, and immigration rate, and showed how incorporating these extensions to Malécot's theory of isolation-by-distance allows us to accurately reconstruct observed sex-specific isolation-by-distance patterns in autosomal and Z-linked SNPs. Therefore, patterns of fine-scale isolation-by-distance in the Florida Scrub-Jay can be well understood as a result of limited dispersal over contemporary timescales.

Genomic Consequences of Population Decline in the Endangered Florida Scrub-Jay.

Understanding the population genetic consequences of declining population size is important for conserving the many species worldwide facing severe decline [1]. Thorough empirical studies on the impacts of population reduction at a genome-wide scale in the wild are scarce because they demand huge field and laboratory investments [1, 2]. Previous studies have demonstrated the importance of gene flow in introducing genetic variation to small populations [3], but few have documented both genetic and fitness consequences of decreased immigration through time in a natural population [4-6]. Here we assess temporal variation in gene flow, inbreeding, and fitness using longitudinal genomic, demographic, and phenotypic data from a long-studied population of federally Threatened Florida scrub-jays (Aphelocoma coerulescens). We exhaustively sampled and genotyped the study population over two decades, providing one of the most detailed longitudinal investigations of genetics in a wild animal population to date. Immigrants were less heterozygous than residents but still introduced genetic variation into our study population. Owing to regional population declines, immigration into the study population declined from 1995-2013, resulting in increased levels of inbreeding and reduced fitness via inbreeding depression, even as the population remained demographically stable. Our results show that, contrary to conventional wisdom, small peripheral populations that already have undergone a genetic bottleneck may play a vital role in preserving genetic diversity of larger and seemingly stable populations. These findings underscore the importance of investing in the persistence of small populations and maintaining population connectivity in conservation of fragmented species.

Selection and inheritance of sexually dimorphic juvenile plumage coloration.

Sexually dimorphic plumage coloration is widespread in birds and is generally thought to be a result of sexual selection for more ornamented males. Although many studies find an association between coloration and fitness related traits, few of these simultaneously examine selection and inheritance. Theory predicts that sex-linked genetic variation can facilitate the evolution of dimorphism, and some empirical work supports this, but we still know very little about the extent of sex linkage of sexually dimorphic traits. We used a longitudinal study on juvenile Florida scrub-jays (Aphelocoma coerulescens) to estimate strength of selection and autosomal and Z-linked heritability of mean brightness, UV chroma, and hue. Although plumage coloration signals dominance in juveniles, there was no indication that plumage coloration was related to whether or not an individual bred or its lifetime reproductive success. While mean brightness and UV chroma are moderately heritable, hue is not. There was no evidence for sex-linked inheritance of any trait with most of the variation explained by maternal effects. The genetic correlation between the sexes was high and not significantly different from unity. These results indicate that evolution of sexual dimorphism in this species is constrained by low sex-linked heritability and high intersexual genetic correlation.

Hatching asynchrony that maintains egg viability also reduces brood reduction in a subtropical bird.

In birds, hatching failure is pervasive and incurs an energetic and reproductive cost to breeding individuals. The egg viability hypothesis posits that exposure to warm temperatures prior to incubation decreases viability of early laid eggs and predicts that females in warm environments minimize hatching failure by beginning incubation earlier in the laying period, laying smaller clutches, or both. However, beginning incubation prior to clutch completion may incur a cost by increasing hatching asynchrony and possibly brood reduction. We examined whether Florida scrub jays (Aphelocoma coerulescens) began incubation earlier relative to clutch completion when laying larger clutches or when ambient temperatures increased, and whether variation in incubation onset influenced subsequent patterns of hatching asynchrony and brood reduction. We compared these patterns between a suburban and wildland site because site-specific differences in hatching failure match a priori predictions of the egg viability hypothesis. Females at both sites began incubation earlier relative to clutch completion when laying larger clutches and as ambient temperatures increased. Incubation onset was correlated with patterns of hatching asynchrony at both sites; however, brood reduction increased only in the suburbs, where nestling food is limiting, and only during the late nestling period. Hatching asynchrony may be an unintended consequence of beginning incubation early to minimize hatching failure of early laid eggs. Food limitation in the suburbs appears to result in increased brood reduction in large clutches that hatch asynchronously. Therefore, site-specific rates of brood reduction may be a consequence of asynchronous hatching patterns that result from parental effort to minimize hatching failure in first-laid eggs. This illustrates how anthropogenic change, such as urbanization, can lead to loss of fitness when animals use behavioral strategies intended to maximize fitness in natural landscapes.

The effects of low levels of light at night upon the endocrine physiology of western scrub-jays (Aphelocoma californica).

Florida scrub-jays (Aphelocoma coerulescens) in the suburbs breed earlier than jays in native habitat. Amongst the possible factors that influence this advance (e.g., food availability, microclimate, predator regime, etc.), is exposure to artificial lights at night (LAN). LAN could stimulate the reproductive axis of the suburban jays. Alternatively, LAN could inhibit pineal melatonin (MEL), thus removing its inhibitory influence on the reproductive axis. Because Florida scrub-jays are a threatened species, we used western scrub-jays (Aphelocoma californica) to investigate the effects of LAN upon reproductive hormones and melatonin. Jays were held under conditions in which the dark-phase of the light:dark cycle was without illumination and then under low levels of LAN. Under both conditions, birds were exposed first to short-days (9.5L:14.5D) that were gradually increased to long-days (14.5L:9.5D). At various times, blood samples were collected during the light part of the cycle to measure reproductive hormones (luteinizing hormone, LH; testosterone, T; and estradiol, E2 ). Similarly, samples to assess melatonin were collected during the dark. In males, LAN caused a depression in LH levels and levels were ∼4× greater under long- than short-days. In females, there was no effect of LAN or photoperiod upon LH. LAN resulted in depressed T levels in females, although there was no effect on T in males. E2 levels in both sexes were lower under LAN than under an unlighted dark-phase. Paradoxically, MEL was higher in jays under LAN, and under long-days. MEL did not differ by sex. LAN disrupted the extraordinarily strong correlation between T and E2 that existed under unlighted nocturnal conditions. Overall, our findings fail to support the hypothesis that LAN stimulates the reproductive axis. Rather, the data demonstrate that LAN tends to inhibit reproductive hormone secretion, although not in a consistent fashion between the sexes.

Mind the gap: genetic distance increases with habitat gap size in Florida scrub jays.

Habitat gap size has been negatively linked to movement probability in several species occupying fragmented landscapes. How these effects on movement behaviour in turn affect the genetic structure of fragmented populations at local scales is less well known. We tested, and confirmed, the hypothesis that genetic differentiation among adjacent populations of Florida scrub jays--an endangered bird species with poor dispersal abilities and a high degree of habitat specialization--increases with the width of habitat gaps separating them. This relationship was not an artefact of simple isolation-by-distance, as genetic distance was not correlated with the Euclidean distance between geographical centroids of the adjacent populations. Our results suggest that gap size affects movement behaviour even at remarkably local spatial scales, producing direct consequences on the genetic structure of fragmented populations. This finding shows that conserving genetic continuity for specialist species within fragmented habitat requires maintenance or restoration of preserve networks in which habitat gaps do not exceed a species-specific threshold distance.

Circulating carotenoid concentrations are positively correlated with later clutch initiation in Florida Scrub-Jays (Aphelocoma coerulescens).

Antioxidants play key roles in preventing free radical damage to various molecules, cells, and tissues, but it is not well understood how variation in antioxidant levels may relate to the reproductive success or health of wild animals. We explored the relationship between circulating antioxidant concentrations and both body condition and timing of reproduction in male and female Florida Scrub-Jays (Aphelocoma coerulescens), a cooperatively breeding passerine bird. We examined whether levels of uric acid, vitamin E, and carotenoids (all potentially important antioxidants) were linked to body condition and timing of reproduction, two measures that are directly related to reproductive success. Antioxidant concentrations were not correlated with body condition, but they were related to timing of first clutch initiation, though not always in the predicted direction. Elevated circulating levels of carotenoids were associated with delayed clutch initiation in female breeders. Relatively higher vitamin E levels in control birds were associated with earlier clutch initiation, whereas male breeders that received long-term food supplementation had elevated levels of vitamin E and delayed reproduction. Several potential explanations for the link between elevated levels of antioxidants and delayed clutch initiation are discussed. Separate explanations for each sex include, but are not limited to, oxidative stress as a result of territory defense efforts in males, different dietary regimes due to supplementation, and mobilized plasma antioxidants in females that were coping with a stressor.

Effects of habitat fragmentation on effective dispersal of Florida scrub-jays.

Studies comparing dispersal in fragmented versus unfragmented landscapes show that habitat fragmentation alters the dispersal behavior of many species. We used two complementary approaches to explore Florida Scrub-Jay (Aphelocoma coerulescens) dispersal in relation to landscape fragmentation. First, we compared dispersal distances of color-marked individuals in intensively monitored continuous and fragmented landscapes. Second, we estimated effective dispersal relative to the degree of fragmentation (as inferred from two landscape indexes: proportion of study site covered with Florida Scrub-Jay habitat and mean distance to nearest habitat patch within each study site) by comparing genetic isolation-by-distance regressions among 13 study sites having a range of landscape structures. Among color-banded individuals, dispersal distances were greater in fragmented versus continuous landscapes, a result consistent with other studies. Nevertheless, genetic analyses revealed that effective dispersal decreases as the proportion of habitat in the landscape decreases. These results suggest that although individual Florida Scrub-Jays may disperse farther as fragmentation increases, those that do so are less successful as breeders than those that disperse short distances. Our study highlights the importance of combining observational data with genetic inferences when evaluating the complex biological and life-history implications of dispersal.

Temporal predictability in food availability: effects upon the reproductive axis in Scrub-Jays.

Florida Scrub-Jays (Aphelocoma coerulescens) in a suburban environment with year-round access to multiple sources of abundant, human-source foods consistently breed earlier each year and have lower baseline levels of circulating corticosterone (CORT) than jays in a nearby wildland setting. These findings suggest that food supplies influence CORT levels, which in turn may partially determine the timing of reproduction. However, wildland birds with access to high-quality supplemental foods did not advance breeding or lower CORT levels to the degree observed in the suburbs. Therefore, rather than quality or quantity of food consumed, the perception of a reliable and predictable food supply may be an important factor in determining laying dates. If a predictable food supply accelerates the reproductive process, it follows that food provided on an unpredictable schedule may slow reproduction. We subjected captive Western Scrub-Jays (A. californica) to a 30-day photoperiod transition from short- to long-days and tested whether birds with access to food on an unpredictable schedule exhibited delayed or reduced production of reproductive hormones compared with birds given food on a predictable schedule. Baseline CORT concentrations increased slightly during the experiment, but did not differ between treatment groups. Birds with unpredictable food had slightly lower testosterone levels relative to controls, but there was no effect on estradiol or luteinizing hormone. Our findings offer weak support for the hypothesis that an unpredictable food supply will delay the onset of reproduction; however, the artificial lab environment may limit the application of these findings to free-living populations.

Baseline and acute levels of corticosterone in Florida Scrub-Jays (Aphelocoma coerulescens): effects of food supplementation, suburban habitat, and year.

Recent work has shown that Florida Scrub-Jays (Aphelocoma coerulescens) living in suburban habitats, as well as birds that reside in a natural habitat (hereafter referred to as wildland birds) provided supplemental food during the pre-breeding period, have lower baseline corticosterone (CORT) levels than nonsupplemented wildland birds, suggesting that predictable and abundant foods can lower stress levels. Here, we investigate whether the acute CORT response to capture stress reflects our earlier findings. During the pre-breeding seasons in 2004 and 2005 we captured over 200 Florida Scrub-Jays and collected four blood samples from each bird over a 30 min time period. We compared hormonal and morphometric data from birds in four treatment groups: wildland birds that were provided with supplemental food during the pre-breeding period, wildland birds that were provided with supplemental food during the winter and pre-breeding period, nonsupplemented wildland birds, and suburban birds that effectively have access to ad libitum human-source food year-round. Suburban birds had lower baseline levels, and a more acute initial CORT response (i.e., rate of increase) than wildland birds, but we did not observe any differences among the treatment groups of wildland birds. Baseline CORT concentrations were unusually low across treatments in 2005, a year that was characterized by increased adult body mass, superior body condition, and a high fledgling success rate, all of which suggest favorable environmental conditions. Thus, abundant or more reliable food sources in 2005 may have overwhelmed any potential benefits of supplemental feeding and explain the absence of any strong experimental effects on CORT for that year.

Corticosterone administration does not affect timing of breeding in Florida scrub-jays (Aphelocoma coerulescens).

Providing supplemental food to Florida scrub-jays (Aphelocoma coerulescens) causes a reliable advance in clutch initiation of 1 to 2 weeks. In some years, supplemental food appeared to not only advance laying date but also decrease baseline concentrations of corticosterone (CORT) relative to controls. The coincidence of low CORT levels and early breeding led us to hypothesize that CORT serves to communicate information about environmental conditions to the hypothalamic-pituitary-gonadal (HPG) axis, which ultimately influences the timing of breeding. To test this hypothesis, we administered small oral doses of CORT three times each day to female breeders that were provisioned with supplemental food. We compared clutch initiation dates of the CORT-dosed females to females with supplementation but no exogenous CORT and to females with neither CORT nor supplemental food. CORT administration had a strong temporary effect on circulating CORT concentrations but clutch initiation did not differ between the two groups of supplemented birds, both of which laid eggs approximately 10 days earlier than nonsupplemented birds. Furthermore, during the year of our study we found no reduction in baseline CORT concentrations in our undosed supplemental groups, as had been observed in past studies.