Aphelocoma Coerulescens Research Articles

Does optimal foraging theory explain why suburban Florida scrub-jays (Aphelocoma coerulescens) feed their young human-provided food?

Optimal foraging theory assumes that a forager can adequately assess the quality of its prey and predicts that parents feed their young low-quality foods only when suffering unpredicted reductions in their ability to provision. Wildland Florida scrub-jays feed their young exclusively arthropods, but suburban parents include human-provided foods in the nestling diet, with possible costs in terms of reduced growth and survival. We tested experimentally whether parents feed human-provided foods, given the apparent costs, because: 1) they do not discriminate between food types, 2) they switch to low-quality, abundant foods when natural food availability in the environment is low, or 3) they switch when the time needed to obtain natural food is high. Parents discriminated between natural and human-provided foods by showing a preference for natural foods when rearing young. When the handling time of natural foods was increased experimentally, parents in the suburban and wildland habitats switched to human-provided foods. Supplementation with natural foods increased preference for this food in both habitats. Suburban parents chose more natural foods than wildland parents, suggesting that they have a greater preference for natural foods. Regardless of preferences demonstrated at feeders, parents in both the suburbs and wildlands delivered mostly natural foods to nestlings, independent of natural food availability. Nonetheless, natural foods are likely to be scarcer in the environment than in our experimental tests. Because natural food availability is lower in the suburbs than in the wildland habitat, parents in the suburbs may be forced to switch to human-provided foods when feeding nestlings.

Living with the Trickster: Crows, Ravens, and Human Culture

Living with the Trickster: Crows, Ravens, and Human Culture

Landcover characterizations and Florida scrub-jay ( Aphelocoma coerulescens) population dynamics

Landcover maps demarcate habitat but might underestimate it where species select features smaller than minimum mapping units used to produce maps. Habitat loss is magnified by fragmentation, which produces edge effects, alters dispersal and natural processes (i.e., fire). We quantified how Florida scrub-jay ( Aphelocoma coerulescens) habitat varied using traditional landcover maps and methods that considered small focal habitat features (e.g., scrub ridges <2 ha) within an otherwise unsuitable matrix. We collected 7 years of data on color banded Florida scrub-jays to quantify dispersal and investigate how reproductive success and survival varied with habitat potential (scrub ridges), edge effects, and fire history. Landcover maps that identified only large scrub ridges resulted in a potential population of 354 pairs. Including small scrub ridges within an otherwise unsuitable matrix resulted in a potential population >774 pairs. Florida scrub-jays occupied less than half the potential habitat, and their population declined most from disrupted fire regimes. Almost 90% of all breeding dispersers remained within the same cluster of territories that they hatched in emphasizing the need to maximize local habitat quantity and quality. Reduced habitat quality, caused by disrupted fire regimes, was a major fragmentation effect that greatly magnified impacts of habitat loss. The disruption of natural processes is seldom identified as a major fragmentation effect, but studies worldwide have accumulated to demonstrate its significance. We advocated specific mapping approaches for species influenced by small habitat features and species dependent on matrix habitats that advance natural processes, such as fire.

Pre-ingestive treatment of bombardier beetles by jays: food preparation by “anting” and “sand-wiping”

Evidence is presented, obtained with two species of jays, that these birds differ in the ways in which they prepare bombardier beetles for ingestion. Blue Jays subject bombardiers to “anting,” a procedure by which the beetles are induced to eject their spray into the plumage of the birds. Florida Scrub Jays, in contrast, which live in an area where the soil is sandy, subject bombardiers to “sand-wiping,” causing the beetles to eject their spray into the substrate. Both strategies lend themselves also to pre-ingestive treatment of other chemically protected arthropods. Anting is a strategy widely practiced by birds, possibly because it can be put to use no matter what the nature of the terrain. Sand-wiping, as implied by its name (which we here coin), may be of more restricted occurrence, given that it can be carried out only on loose, penetrable soil.

Avian Host and Mosquito (Diptera: Culicidae) Vector Competence Determine the Efficiency of West Nile and St. Louis Encephalitis Virus Transmission

The ability of the invading NY99 strain of West Nile virus (WNV) to elicit an elevated viremia response in California passerine birds was critical for the effective infection of Culex mosquitoes. Of the bird species tested, Western scrub jays, Aphelocoma coerulescens, produced the highest viremia response, followed by house finches, Carpodacus mexicanus, and house sparrows, Passer domesticus. Most likely, few mourning, Zenaidura macroura, or common ground, Columbina passerine, doves and no California quail, Callipepla californica, or chickens would infect blood-feeding Culex mosquitoes. All Western scrub jays and most house finches succumbed to infection. All avian hosts produced a lower viremia response and survived after infection with an endemic strain of St. Louis encephalitis virus. Culex species varied in their susceptibility to infection with both viruses, with Culex stigmatosoma Dyar generally most susceptible, followed by Culex tarsalis Coquillett, and then Culex p. quinquefasciatus Say. Populations within Culex species varied markedly in their susceptibility, perhaps contributing to the focality of WNV amplification. Transmitting female Cx. tarsalis expectorated from six to 3,777 plaque-forming units (PFU) of WNV during transmission trials, thereby exposing avian hosts to a wide range of infectious doses. Highly susceptible house finches and moderately susceptible mourning doves were infected by subcutaneous inoculation with decreasing concentrations of WNV ranging from 15,800 to <0.3 PFU. All birds became infected and produced comparable peak viremias on days 2-3 postinoculation; however, the rise in viremia titer and onset of the acute phase of infection occurred earliest in birds inoculated with the highest doses. WNV virulence in birds seemed critical in establishing elevated viremias necessary to efficiently infect blood feeding Culex mosquitoes.

Food supplementation and possible mechanisms underlying early breeding in the Florida Scrub-Jay ( Aphelocoma coerulescens)

Food supplementation studies demonstrate the importance of resources in the timing of reproduction. Studies of Florida Scrub-Jays ( Aphelocoma coerulescens) found that supplemented jays bred earlier than unsupplemented jays and that protein may play a critical role. In this study, free-living scrub-jays were provided with supplemental diets high in fat and protein (HFHP) or high in fat and low in protein (HFLP). Jays in both treatments bred earlier than unsupplemented controls (CNT), but HFHP-supplemented jays bred earlier than HFLP jays. To assess possible mechanisms, we measured testosterone (T) in males, estradiol (E 2) in females, and corticosterone (CORT) in both. HFHP males had higher T than HFLP and CNT males, but treatment did not affect E 2 levels of females. Pilot studies of scrub-jays in suburban environments suggest that the spatial and temporal predictability of food may influence corticosterone (CORT) levels. Suburban jays have year-round access to human-provided foods and breed earlier than wildland jays; thus, we compared CORT in all treatments in the natural site ( wildlands) with those of suburban jays. CORT levels of suburban jays were lower than HFLP, HFHP, and CNT jays. HFHP-supplemented jays had lower CORT levels than those of HFLP and CNT jays. The observed differences in the timing of breeding, both between suburban and wildland populations and between experimental groups in the wildlands, may result from differences in the spatial and temporal predictability of food, and the nutritional differences in diets. Because CORT can negatively affect the reproductive axis, we postulate that nutrient availability, the predictability of food, CORT levels, and initiation of reproduction are inextricably linked.

Why is brood reduction in Florida scrub-jays higher in suburban than in wildland habitats?

In a population of Florida scrub-jays, Aphelocoma coerulescens (Bosc, 1795), in a suburban scrub habitat, partial brood loss is much more common (averaging about 30% of nestlings from successful nests) than in a natural habitat (averaging about 5%). We hypothesized that this partial brood loss was attributable to starvation of last-hatched nestlings (i.e., brood reduction), and that large differences in partial brood loss were caused by differences in arthropod food abundance between the two sites. To test these hypotheses, we closely monitored nests in suburban scrub in 1999 and performed arthropod surveys and focal-nest observations in both habitats in 1998 and 1999. In suburban scrub, later hatched nestlings were three times more likely to die before fledging than earlier hatched nestlings, suggesting that brood reduction occurred. In both years, arthropod abundance in the suburban scrub was less than half that of the natural scrub. However, patterns of food delivery by parents were not significantly different between sites, suggesting that lower food abundance does not in itself explain higher partial brood loss in suburban habitat. Differences in the number of helpers, a greater degree of hatching asynchrony or the delivery of lower quality food throughout the nestling period may increase the probability that later hatched nestlings starve in suburban scrub.

DO HABITAT POTENTIAL, POPULATION DENSITY, AND FIRES INFLUENCE SCRUB‐JAY SOURCE–SINK DYNAMICS?

The concept of source and sinks can guide conservation, but empirical studies are needed to demonstrate that this concept applies to the real world. We investigated whether the source–sink concept could help to clarify the influence of habitat potential (scrub ridge characteristics), population density, and fires (shrub heights) on Florida Scrub‐Jay (Aphelocoma coerulescens) demography and dispersal. We mapped territories and measured survival, recruitment, emigration, immigration, and shrub heights annually for 12 years. We classified territories as oak if they overlapped well‐drained ridges, oak–palmetto if they overlapped poorly drained ridges &gt;0.4 ha, and palmetto–oak if they only overlapped poorly drained ridges &lt;0.4 ha. Territory size differed little among these categories but was negatively correlated with the annual number of breeding pairs, which ranged from 12 to 27. Scrub ridge characteristics influenced the locations of sinks and potential sources, whereas population density and fires caused temporal variation in demographic success. Oak territories were usually sources because they were net exporters of individuals and because recruitment exceeded mortality. Oak–palmetto territories sometimes functioned as sources but were often pseudo‐sinks because density dependence caused mortality to exceed recruitment. Palmetto–oak territories were true sinks because they were net importers of individuals and mortality exceeded recruitment regardless of population density. All scrub was short (&lt;1.2 m) or medium height (1.2–1.7 m), but the spatial arrangement of these height classes changed regularly because fires occurred every 2–7 years. We observed a quadratic relationship between demographic success and the area of medium‐height scrub within territories. Territories that had 0.9–1.2 ha of medium‐height scrub had the highest demographic success. Applying source–sink concepts at the territory scale was useful to quantify habitat variation at a spatial scale relevant to population processes, reserve design, and habitat management. Our approach can be applied by using territory maps or geographic information systems to partition heterogeneous landscapes into territories and then by classifying territories into potential sources and sinks using scrub ridge characteristics and shrub heights.

Metal and metalloid concentrations in the eggs of threatened Florida scrub-jays in suburban habitat from south-central Florida

Monitoring and assessing changes in contaminants in urban and suburban environments is essential to assessing ecosystem well-being in human-influenced landscapes. We analyzed metal and metalloid levels in the eggs of the threatened Florida scrub-jay ( Aphelocoma coerulescens), an extremely sedentary and modestly long-lived passerine bird that is federally threatened and endemic only in Florida. Eggs that failed to hatch were collected in a suburban environment to compare with the long-term study of this species at the Archbold Biological Station, located 8 km south in a more rural part of south-central Florida. Florida scrub-jays remain in a permanent territory in scrub oak habitat where they feed mainly on insects and acorns, but in suburban habitats human-provided foods comprise 30% of their diet. From the data previously collected at Archbold, and their low position on the food chain, we expected levels of contaminants to be comparatively low and remain relatively constant over time. Except for the low mercury value, all means were within the range of mean values reported for a wide range of non-passerine species (including those at higher tropic levels), are lower than concentrations associated with abnormalities in birds, and are lower than those previously reported for scrub-jays from Archbold Biological Station. A significant increase in selenium occurred from 1996 to 2001, but did not appear associated with changes in human density.

Arboviral infection in two species of wild jays (Aves: Corvidae): evidence for population impacts.

We examined the prevalence of antibodies to three mosquito-borne arboviruses in blue jays, Cyanocitta cristata, and Florida scrub-jays, Aphelocoma coerulescens, to identify the effects on host survival, the influence of sex and age on infection, and the temporal patterns of antibody prevalence. Blood samples from 306 blue jays and 219 Florida scrub-jays were collected at Archbold Biological Station (Lake Placid, FL) from April 1994 through December 1995. Sera were analyzed for hemagglutination-inhibition antibody to eastern equine encephalitis (EEE) and St. Louis encephalitis (SLE) viruses, and neutralizing antibodies to EEE, Highlands J (HJ), and SLE viruses. Overall, 31.4% of blue jay samples and 22.1% of scrub-jay samples had antibodies to EEE. Antibodies to HJ were detected in slightly >15% of samples in each jay species, and SLE was detected in <3% of the samples in each jay species. A single EEE virus isolation was made from the blood of an 11-d-old scrub-jay nestling. Survival of adult blue jays seropositive to EEE was significantly lower than that of seronegative birds based on resight rates, but infection did not seem to affect survival of adult or juvenile Florida scrub-jays.

Florida Scrub-Jays eject foreign eggs added to their nests

Abstract Brown-headed Cowbirds (Molothrus ater), and to a lesser extent Shiny Cowbirds (M. bonariensis), have expanded their breeding ranges to include that of the Florida Scrub-Jay (Aphelocoma coerulescens). We added the eggs of seven bird species to Florida Scrub-Jay nests to determine if scrub-jays eject foreign eggs. Most eggs were ejected within 1 d of addition, probably by grasp-ejection. Ejection of foreign eggs by Florida Scrub-Jays suggests that cowbirds, should they begin to parasitize scrub-jays, would waste their reproductive effort. Fossil evidence suggests that Florida Scrub-Jays may be former cowbird hosts that have sustained the ability to eject.

Florida Scrub‐Jays (Aphelocoma coerulescens) are Sentinels More When Well‐Fed (Even with no Kin Nearby)

AbstractSentinels occupy high, exposed positions while other group members forage nearby. If sentinel behavior involves a foraging–predation risk trade‐off, animals should be sentinels more when fed supplemental food. When individual Florida scrub‐jays (Aphelocoma coerulescens) were fed fragments of peanuts, during the following 30 min they shifted 30% of their time from foraging to sentinel behavior. In a follow‐up experiment, we fed either one or two members in each group. As before, the jays reduced their foraging and spent much more time as sentinels when given supplemental food. In each treatment, pairs were sentinels simultaneously considerably less often than expected by chance. The dramatic shift from foraging to sentinel behavior suggests that for Florida scrub‐jays sentinel behavior brings substantial benefits for no greater cost than that of lost opportunities to forage. Because the results held for simple mated pairs of scrub‐jays, we argue that kin selection and social prestige are not necessary to explain sentinel behavior.

Diet quality during pre‐laying and nestling periods influences growth and survival of Florida scrub‐jay (Aphelocoma coerulescens) chicks

AbstractFood availability is one of the most important determinants of successful reproduction in birds. In a previous study, it was shown that Florida scrub‐jays Aphelocoma coerulescens maintained a third egg mass when supplemented with a high fat and high protein diet during pre‐breeding, as opposed to birds that were not supplemented that laid third eggs markedly lighter in mass than first‐ and second‐laid eggs. Increases in egg quality promote chick growth and survival in many avian species. In this study, scrub‐jays were provided with supplements throughout the pre‐laying and nestling periods of 2001 and 2002 to investigate whether diet quality influenced growth and survival of chicks. Fledging success and survival to independence of unsupplemented chicks were higher for 2002 compared with 2001 indicating that breeding conditions (e.g. natural food availability) for jays were probably improved in the former year. Consistent growth patterns were found during the first 11 days post‐hatch between chicks on supplemented and those on unsupplemented territories. Of the three growth measures, only seventh primary feather growth tended to be greater for third‐hatched chicks on supplemented territories compared with third‐hatched chicks on control territories. Food supplementation influenced survival of chicks. Compared with chicks hatching on unsupplemented territories, fledging success of chicks hatching from second‐laid eggs was significantly greater in 2001, but not in 2002. Chicks from third‐laid eggs on supplemented territories also tended to survive better in 2001 compared with chicks from unsupplemented territories, but, again, no such effect was found in 2002. We conclude that food supplementation in the pre‐laying and nestling periods results in little measurable improvement in chick growth. However, improvements were found in survival of chicks that may be mediated through improvements in egg quality, but also may be the result of changes in foraging strategies of provisioning birds on supplemented territories. Chicks on supplemented territories might be in better body condition than those on unsupplemented ones. Methods other than morphometrics may be required to detect elevations in body condition of chicks raised on supplemented territories.

Does Differential Access to Protein Influence Differences in Timing of Breeding of Florida Scrub-Jays (Aphelocoma Coerulescens) in Suburban and Wildland Habitats?

Abstract Timing of breeding in Florida Scrub-Jays (Aphelocoma coerulescens) varies both within and between years. Social status and breeding experience may explain much of the within-year variation, but the availability of certain foods may partially explain between-year patterns. Scrub-jays in suburban habitats with access to unlimited human-provided foods breed earlier and with less between-year variation in timing of breeding than jays in wildland habitats. We hypothesized that those differences in timing of breeding result from access to human-provided foods in the suburban site. Human-provided food may influence timing of breeding by improving the overall body condition of females, or it may influence breeding by providing nutrients essential for breeding. If condition mediated, breeding females in the two habitats should differ in certain physiological parameters relative to time before egg laying and calendar date. If the effect is not related to body condition, we expect differences in prebreeding females relative to calendar date, but not in relation to time before egg laying. To test those predictions, we measured plasma levels of total protein, calcium, luteinizing hormone, and estradiol. We also measured variables associated with body condition—body mass, a size-corrected condition index, and total body lipids. Most variables tended to increase with both days before laying and calendar date, except total body lipids, which decreased. Suburban females had higher levels of plasma protein relative to both days before egg laying and calendar date than female breeders in the wildland habitat. Luteinizing hormone differed between sites relative to calendar date but not days before laying. Our data suggest that suburban scrub-jays with access to predictable sources of high-quality human-provided foods accumulate endogenous protein that can be used to breed earlier.

Does Differential Access to Protein Influence Differences in Timing of Breeding of Florida Scrub-Jays (Aphelocoma coerulescens) in Suburban and Wildland Habitats?

Does Differential Access to Protein Influence Differences in Timing of Breeding of Florida Scrub-Jays (Aphelocoma coerulescens) in Suburban and Wildland Habitats?

Variation in Foraging Behavior, Diet, and Time of Breeding of Florida Scrub-Jays in Suburban and Wildland Habitats

Abstract Supplemental food enables some birds to lay eggs earlier, perhaps by allowing birds to increase their energy intake or allocate energy from other activities to reproduction. We examined the relationships between prelaying behavior, food handling and consumption rates, and the timing of breeding of female Florida Scrub-Jays (Aphelocoma coerulescens) in suburban and wildland habitats. Scrub-jays in suburban habitats had access to ad libitum human-provided foods; wildland jays did not. During both years of this study, suburban scrub-jays bred earlier than their wildland counterparts. Wildland scrub-jays bred earlier in 1997 than in 1996, but the timing of breeding by suburban scrub-jays did not vary between years. Suburban scrub-jays spent less time foraging and more time perching than wildland jays. They handled more food per hour and per foraging hour, suggesting their foraging was more efficient. Despite this, food consumption rates did not differ between the two habitats. Neither time spent foraging or perching nor food consumption rates significantly influenced variation in time of breeding among individuals. Time of breeding was significantly influenced by site, year, and rate of food handling. Individuals that handled more food items per foraging hour, that is, those individuals that were most efficient, were the earliest breeders in both habitats. These results suggest that foraging efficiency increases with access to human-provided food and that resource predictability may be a perceptual cue for the appropriate timing of breeding. Variación en el Comportamiento de Forrajeo, la Dieta y la Época de Reproducción de Aphelocoma coerulescens en Ambientes Suburbanos y Silvestres Resumen. El alimento suplementario le permite a algunas aves poner huevos más temprano, quizás aumentando su ingestión de energía o permitiendo cambiar la asignación de energía de otras actividades a la reproducción. En este estudio examinamos las relaciones entre el comportamiento pre-postura, la manipulación de alimento y la tasa de consumo con la época de reproducción de hembras de la especie Aphelocoma coerulescens en ambientes suburbanos y silvestres. Las aves en ambientes suburbanos tenían acceso a alimento provisto ad libitum por humanos, mientras que las aves de las áreas silvestres no. Durante los dos años de estudio, las aves suburbanas se reprodujeron más temprano que las de las áreas silvestres. Las aves de áreas silvestres se reprodujeron más temprano en 1997 que en 1996, pero la época reproductiva de las aves de áreas suburbanas no varió entre años. Las aves suburbanas pasaron menos tiempo forrajeando y más tiempo perchadas que las de áreas silvestres, y además manipularon más alimento por hora y por hora de forrajeo, lo que sugiere que forrajearon más eficientemente. Sin embargo, las tasas de consumo de alimento no difirieron entre los dos ambientes. La variación entre individuos en el momento de la reproducción no fue influenciada significativamente por el tiempo invertido en forrajeo o descanso ni por la tasa de consumo de alimento, pero sí por el sitio, el año y la tasa de manipulación de alimento. Los individuos que manipularon más ítems alimenticios por sesión de forrajeo (los más eficientes), fueron los que se reprodujeron más temprano en ambos ambientes. Estos resultados sugieren que la eficiencia de forrajeo aumenta con el acceso a alimentos provistos por humanos y que la predecibilidad de los recursos podría ser percibida como una señal indicadora del momento de reproducción adecuado.

Apparent Cooperative Hunting in Florida Scrub-Jays

I observed an apparent coordinated attack by a mated pair of Florida Scrub-Jays (Aphelocoma coerulescens) on a black racer (Coluber constrictor) in southcentral Florida. Depending upon their size, snakes can be either prey or predators of scrub-jays. This medium-sized snake may have been large enough that one bird could not safely subdue it. By coordinating their attack, the birds were able to kill and feed on the snake. This appears to be an example of pair hunting. The cooperative hunting technique, in which two mated birds perform coordinated movements, enables the pair to attack otherwise prohibitively large prey. Both members of the attack benefit by eating the prey. Cooperative hunting has only rarely been described in passerines.

TERRITORY QUALITY TRANSITIONS AND SOURCE–SINK DYNAMICS IN A FLORIDA SCRUB-JAY POPULATION

Source–sink theory provides an approach to identify habitat arrangements needed to sustain populations in spatially and temporally varying landscapes. Our objective was to investigate whether source–sink ideas could be applied to quantify how habitat arrangements influenced Florida Scrub-Jay (Aphelocoma coerulescens) population dynamics, in order to enhance habitat restoration. From 1988 to 2001, we measured reproductive success, survival, immigration, emigration, pair bond fidelity, and the duration of delayed breeding by young. The arrangement of shrub height in each territory was used to classify habitat quality each year, according to the following categories: short (<120 cm tall), optimal (short plus 120–170 cm tall), tall mix (short or optimal and >170 cm), and tall (>170 cm). Annual demographic performance rates were calculated in each territory by summing the recruitment of potential breeders (the number of yearlings produced) and then subtracting the number of breeders that died. The mean demographic performance per breeding pair was −0.57, 0.33, −0.26, and −0.35, respectively, for short, optimal, tall mix, and tall territories. Optimal territories functioned as sources because recruitment exceeded mortality; hence, the optimal territories were net exporters to marginal habitat. Potential breeders were exported to sink territories by active dispersal and by “territory quality transitions,” whereby territories produced an excess of potential breeders while in optimal condition and then became marginal because of shifting territory boundaries and habitat conditions. Short, tall mix, and tall territories functioned as sinks because they were net importers, mortality exceeded recruitment, and because there were no density-dependent reductions in their demographic performance. The population declined because there were too few optimal territories to offset declines in sinks, which usually had too much tall scrub even though most of the landscape had been burned recently. Successful habitat restoration requires greater emphases on improving habitat quality at the territory scale because this is the fundamental landscape unit related to demography. Source–sink ideas, complemented by territory quality transitions, provide a quantitative approach to directly relate habitat and demographic objectives. Corresponding Editor: D. J. Levey.

Influence of coloured noise on the extinction risk in structured population models

We use simple models to compare extinction risk among basic life history types when environmental noise is either uncorrelated (“white”) or positively autocorrelated (“red”). The metric of extinction is probability of extinction in 50 years; variability of noise is scaled such that its expected variance is independent of colour at this time scale. We compare annual, semelparous biennial, iteroparous biennial and perennial life histories. Given an identical equilibrium population size and basic reproductive number, annual life history confers much higher extinction risk than semelparous biennial life history. Iteroparous biennial and perennial life histories have even lower extinction risks. Autocorrelated noise influences the life histories differently: the extinction risk of the annuals decreases with reddening noise, whereas the other life histories show an opposite response. We show that in a previously developed stage-structured population model for the Florida scrub jay Aphelocoma coerulescens ignoring the possibility of red environmental noise might result in much too optimistic assessment on population viability. In conclusion, simplifications of population structure and ignoring red environmental noise in population viability analyses can result in serious biases.

Nutritional quality of prebreeding diet influences breeding performance of the Florida scrub-jay.

Food supplementation studies of breeding birds have traditionally concentrated on energetic constraints on breeding performance. It is only recently that the nutritional quality of the prebreeding diet has also been considered influential. We examined the importance of specific nutrients in the prebreeding diet of the Florida scrub-jay ( Aphelocoma coerulescens). Birds were provided with one of two supplements (rich in protein and fat or rich in fat only) prior to breeding in 2000 and 2001 and their breeding performance, in relation to unsupplemented (control) birds, was examined. Birds receiving both supplements significantly advanced laying in both years, and increased clutch size in 2000 but not in 2001. Laying date explained variation in clutch size in birds on dietary supplements. Egg mass and volume declined with laying order, irrespective of dietary treatment, but birds on the high fat, high protein diet laid heavier third eggs than controls and this was independent of laying date. Laboratory analysis of 14 abandoned and unhatched eggs revealed that as egg mass increased so did the absolute amount of protein and water while fat content remained relatively fixed. Using these relationships between the masses of egg components and fresh egg mass, we calculated that heavier third eggs laid by birds on high fat and high protein, compared with those laid by controls, contained more water that may be fundamental to chick growth and survival. This is the first demonstration for an avian species that nutritional quality of prebreeding diet can simultaneously influence laying date, clutch size, and egg size and composition.