Life history strategies of species are finely-tuned to their environment through natural selection. However, human alterations of those environments occur at a variety of ecological and spatial scales; from alterations in the composition and availability of foods, to changes in the structure and composition of vegetative communities, changes in predator community structure and composition, alteration in spatial and temporal regimes of ecological processes such as fire, and broad-scale changes in the structure and composition of entire landscape mosaics. Species may be able to respond to some of these anthropogenic changes or they may be evolutionarily constrained. Research in the Avian Ecology Lab focuses on understanding many of these anthropogenic ecological changes and their impact on birds at a variety of scales, from physiological and behavioral responses to population and community responses. We use a combination of longitudinal, observational studies and controlled experiments to identify ecological patterns and then to test the effects of specific variables. In particular, our research has focused on the effects of urbanization on the demography and social biology of the Florida scrub-jay (Aphelocoma coerulescens) and on the effects of multiple resource management (grazing, forestry, human recreation, military training, and endangered species management) on both Florida scrub-jays and red-cockaded woodpeckers (Picoides borealis), both federally-listed species. Here, we discuss just a few of our research approaches.

Anthropogenic effects on bottom-up mechanisms of population regulation. An active area of theoretical and empirical interest in ecology is the relative importance of top-down (predators and parasites) versus bottom-up (food or productivity) influences on the regulation of populations. Urbanization is likely to strongly affect both the availability of food (reduction in natural foods, availability of anthropogenic foods) and the composition of the predator community (introduction of novel predators and changes in the abundance of native predators). Our research has increasingly focused on bottom-up processes regulating suburban scrub-jay populations. Urbanization does influence predator communities, but these changes do not appear to influence nest success rates of urban-nesting scrub-jays. However, urbanization decreases arthropod populations and scrub-jays in suburban habitats make fewer trips and deliver less food to nestlings than jays in natural habitats. As a consequence, within-brood size asymmetries and brood reduction are higher, and fledgling production and post-fledgling survival are lower than in the jay population at Archbold. To test if these patterns were related to differences in food, we experimentally provisioned young nestlings with a high-protein supplemental diet. Supplementation decreased brood reduction and increased the number of fledglings and their post-fledgling survival, suggesting that diet may be limiting productivity. However, jays readily use anthropogenic sources of food, such as bird feeders, peanuts, and pet foods. Access to supplemental food results in earlier laying dates and decreased between-year variation in laying date. We know little about the cues birds use for making reproductive decisions, but when anthropogenic changes alter the predictive value of those cues, an inappropriate response may occur. Although earlier breeders have better nest success, suburban scrub-jays did poorest relative to scrub-jays in natural habitats when the difference in laying date was greatest. If jays use supplemental food as a cue, they may initiate breeding early in years when arthropod abundance is delayed and delaying breeding is the appropriate response (see Fig. 1, below). To assess the mechanisms by which supplemental food affects timing of breeding, we have collaborated with Steve Schoech to conduct controlled supplemental feeding experiments on jays at Archbold, where we vary the nutritional content of the food. The experiments are designed to assess whether specific nutrients, such as protein or lipids, mediate physiological precursors to breeding or whether the spatial and temporal predictability of food serves as a cue.

Habitat fragmentation and effects on dispersal and metapopulation dynamics. Spatially-explicit population models depend, in part, upon empirical data on the movement patterns of individuals across spatially heterogenous landscapes, yet few of these data exist. Florida scrub-jays are relatively sedentary, frequently dispersing only one or two territories from home. Yet habitat fragmentation reduces the size of habitat patches, reducing the number of contiguous jay territories, increases the distance between patches, and alters the habitat types that occupy the matrix (see map, this page). Jays may readily move when they can perceive other jay territories, but some may decide to disperse beyond their perceptual limits. We developed a series of logistic regression models to examine under which set of demographic, social, and landscape conditions are male and female jays more likely to disperse beyond their local neighborhood. Females are more likely to disperse beyond their perceptual range than males. Females were more apt to leave if their natal patches consisted of few territories with poor demography success. Males were more apt to leave if they were young, and their natal patches consisted of many territories with good demographic success. Males may leave to avoid competition, but females may leave to improve their probability of finding a mate. We also are using radio-telemetry to assess movement patterns of pre-breeding jays as they explore their landscape and GIS models to examine the characteristics and size distributions of habitat gaps dispersing birds must have crossed to get from one point in a landscape to another. All these data can improve the validity of movement decision rules in spatially-explicit population models. With several outside collaborators, we are using spatially-explicit models to account for the differing effects of habitat fragmentation, isolation, and patch size on the extinction vulnerability of different jay metapopulations.

All our long-term demographic studies on Florida scrub-jays and red-cockaded woodpeckers continue. Cumulatively, we have over 20 years of detailed demographic data from our marked populations of birds.

Fig. 1. Variation in the timing of breeding between Florida scrub-jay populations in suburban and natural scrub and between-year patterns relative to the long-term mean date of first clutch initiation.