Tracking the long-term decline and recovery of an isolated population

Effects of small population size and reduced genetic variation on the viability of wild animal populations remain controversial. During a 35-year study of a remnant population of greater prairie chickens, population size decreased from 2000 individuals in 1962 to fewer than 50 by 1994. Concurrently, both fitness, as measured by fertility and hatching rates of eggs, and genetic diversity declined significantly. Conservation measures initiated in 1992 with translocations of birds from large, genetically diverse populations restored egg viability. Thus, sufficient genetic resources appear to be critical for maintaining populations of greater prairie chickens.     

Use of landscape metrics to predict avian nest survival in a fragmented midwestern forest landscape

Habitat fragmentation fundamentally affects trophic interactions and ecosystem function. Understanding how the landscape matrix modulates such interactions can improve our understanding of fragmentation ecology. Studies of breeding birds provide clear examples of the consequences of habitat fragmentation, but the landscape context of these effects are unclear. We sampled avian nesting success in 12 moderately-large forest patches (>250 ha) embedded in different types of landscapes in southern Illinois, USA. We then evaluated eight models that predicted the probability of nest success and brood parasitism by Brown-headed Cowbirds. These models incorporated landscape composition (% grassland, % agriculture, fragmentation), year and seasonal effects, conspecific density, predator density, and combinations of these variables. Temporal factors (stage of nesting cycle, seasonal effects, annual variation) had the most effect on nesting success; landscape factors had little influence on nesting success. The rate and intensity of brood parasitism were significantly influenced by the amount of grassland for the Wood Thrush, but not for the Acadian Flycatcher. Fine-scale management of the matrix surrounding the patches may dictate the local abundance and movements of nest predators and parasites. Other major nest predators may prefer the forest interior and at least partially compensate for the lower abundance of nest predators that depend upon the matrix. Overall, landscape metrics were weak predictors of avian nesting success in complex landscapes that have diverse predator communities.     

Relationships between avian diversity, neighborhood age, income, and environmental characteristics of an urban landscape

Maintaining biodiversity in urbanizing landscapes has become a top conservation priority. We examined variation in bird communities across a diverse array of urban and suburban neighborhoods in the Chicago, Illinois, metropolitan region. Rather than taking the usual approach of focusing solely on natural features of the urban landscape, we investigated how urban bird communities were related to neighborhood age and income, as well as environmental characteristics. We found that median housing age was strongly related to avian species richness, with newer neighborhoods supporting more species. Housing age was an important correlate of abundance for several species as well as abundance of exotic, migratory, and non-migratory species groups. Per capita income was inversely related to richness of native bird species and positively related to exotic richness. Total richness was higher in urban sites with undeveloped patches and heterogeneous land cover types; moreover, richness decreased with increasing distance from natural areas greater than 1 km². Our findings suggest that bird richness is enhanced both by small patches of natural land within the urban matrix and by close proximity to large natural preserves. Furthermore, these results suggest that investigating a combination of abiotic and environmental features of the built landscape, rather than focusing solely on environmental features, may provide a more complete understanding of the factors influencing avian diversity in human-dominated landscapes.     

Predator activity and predation on songbird nests on forest-field edges in east-central Illinois

We measured the activity of mammalian predators, numbers of singing male songbirds, and predation rates on nests of songbirds (152 natural, open-cup nests and 380 artificial nests) on 38 250 m transects located along various types of forest-field edges in a wildlife management area in east-central Illinois. We then related these variables to each other and to measures of the vegetative structure of our transects that we anticipated might influence predator activity or predation rates on nests of birds characteristic of edge and shrubland habitats. Mammalian predators, particularly raccoons (Procyon lotor), were abundant in the wildlife area and present on all transects surveyed. We did not find significant relationships among the variables we measured. Rather, rates of nest predation were consistently high (>70%) and generally evenly distributed around our study site. Medium-sized, generalist mammalian predators in the midwestern United States reach their highest population densities in fragmented landscapes with abundant edge habitat, particularly agricultural edges. Areas of natural habitat in these landscapes dominated by agriculture may concentrate predators and act as ecological traps for nesting birds because they attract high densities of breeding birds that are subjected to high rates of nest predation.