Territory and population attributes affect Florida scrub-jay fecundity in fire-adapted ecosystems

Fecundity, the number of young produced by a breeding pair during a breeding season, is a primary component in evolutionary and ecological theory and applications. Fecundity can be influenced by many environmental factors and requires long-term study due to the range of variation in ecosystem dynamics. Fecundity data often include a large proportion of zeros when many pairs fail to produce any young during a breeding season due to nest failure or when all young die independently after fledging. We conducted color banding and monthly censuses of Florida scrub-jays (Aphelocoma coerulescens) across 31 years, 15 populations, and 761 territories along central Florida's Atlantic coast. We quantified how fecundity (juveniles/pair-year) was influenced by habitat quality, presence/absence of nonbreeders, population density, breeder experience, and rainfall, with a zero-inflated Bayesian hierarchical model including both a Bernoulli (e.g., brood success) and a Poisson (counts of young) submodel, and random effects for year, population, and territory. The results identified the importance of increasing "strong" quality habitat, which was a mid-successional state related to fire frequency and extent, because strong territories, and the proportion of strong territories in the overall population, influenced fecundity of breeding pairs. Populations subject to supplementary feeding also had greater fecundity. Territory size, population density, breeder experience, and rainfall surprisingly had no or small effects. Different mechanisms appeared to cause annual variation in fecundity, as estimates of random effects were not correlated between the success and count submodels. The increased fecundity for pairs with nonbreeders, compared to pairs without, identified empirical research needed to understand how the proportion of low-quality habitats influences population recovery and sustainability, because dispersal into low-quality habitats can drain nonbreeders from strong territories and decrease overall fecundity. We also describe how long-term study resulted in reversals in our understanding because of complications involving habitat quality, sociobiology, and population density.

Increased lead and glucocorticoid concentrations reduce reproductive success in house sparrows along an urban gradient

Urbanization is increasing at a rapid pace globally. Understanding the links among environmental characteristics, phenotypes, and fitness enables researchers to predict the impact of changing landscapes on individuals and populations. Although avian reproductive output is typically lower in urban compared with natural areas, the underlying reasons for this discrepancy may lie at the intersection of abiotic and biotic environmental and individual differences. Recent advances in urban ecology highlight the effect of heavy metal contamination on stress physiology. As high levels of glucocorticoid hormones decrease parental investment, these hormones might be the link to decreased reproductive success in areas of high environmental pollution. In this study, we aimed to identify which abiotic stressors are linked to avian reproductive output in urban areas and whether this link is mediated by individual hormone levels. We used fine-scaled estimates (2 m2 spatial resolution) of nighttime light, noise, and urban density to assess their impacts on the physiological condition of adult house sparrows (Passer domesticus). We measured circulating levels of lead and glucocorticoid concentrations in 40 breeding pairs of free-living house sparrows and related these physiological traits to reproductive success. Using structural equation modeling, we found that increased urban density levels linked directly to increased plasma corticosterone and lead concentrations that subsequently led to decreased fledgling mass. Sparrows with increased lead concentrations in plasma also had higher corticosterone levels. Although urban areas may be attractive due to decreased natural predators and available nesting sites, they may act as ecological traps that increase physiological damage and decrease fitness. To illustrate, avian development is strongly explained by parental corticosterone levels, which vary significantly in response to urban density and lead pollution. With fine-scale ecological mapping for a species with small home ranges, we demonstrated the presence and impacts of urban stressors in a small city with high human densities.

A spatial gradient analysis of urban Red-tailed Hawk nestling diet

We examined Red-tailed Hawk (Buteo jamaicensis) nestling diets in Reno and Sparks, NV, USA during the 2015 and 2016 breeding seasons. Field researchers and nest cameras recorded 1348 prey items spanning 28 species at 88 nests. Prey consisted of 86% mammalia, 10% aves and 4% reptilia. Differential prey selection occurred among the population and at individual nests relative to an expected diet. Diet breadth differed between nests and increased with urban density. Avian prey consumption increased relative to mammalian and reptilian prey in impervious areas. When prey items were plotted on a continuous urban density spectrum, mammalian prey increased in the suburban areas and decreased toward the urban core and was inversely correlated with avian prey. Mammalian prey consumption increased and decreased at the end of April and in mid-May before increasing through the remainder of the breeding season (mid-June). Avian prey consumption peaked in May and increased through the season, and reptilian prey varied little. The geographic patterns of prey species consumed in our study reflect those in cities elsewhere. As the urban area changes, we predict that the densest populations of Red-tailed Hawks will continue to reside in the suburban areas where prey diversity and abundance are highest. This was one of the first studies to record urban Red-tailed Hawk diet and revealed patterns in how an urban population used food resources.