Archbold Biological Station
Biennial Report 1995-1996
P.O. Box 2057 Lake Placid, Florida 33862 USA
Phone: 863-465-2571 FAX: 863-699-1927
Obtained more than $500,000 in external funding for; suburban scrub-jay project (Florida Game and Fresh Water Fish Commission), scrub-jay research at APAFR and CCAFS (Department of Defense, The Nature Conservancy), and red-cockaded woodpecker research at APAFR and throughout south-central Florida (Department of Defense, U.S. Fish and Wildlife Service, and Florida Game Commission).
Completed an intensive, year-long study of the foraging behavior and foraging habitat characteristics of red-cockaded woodpeckers at APAFR. Entered into a GIS over 5,000 foraging locations that are linked with extensive databases on foraging behavior, demography, and habitat.
Published 5 papers in refereed journals or books, presented 3 invited papers at universities, and 13 papers at professional meetings.
Received, with Hilary Swain, David Breininger, and Paul Schmalzer, the Conservation Colleague Award from The Florida Chapter of The Nature Conservancy for our scientific contributions to developing a reserve design for Brevard Countys Scrub Conservation and Development Plan.
biennial 1995 home page
Applied Avian Ecology
Project Director: Reed Bowman
The structure and composition of avian bird communities often change with anthropogenic ecological change. Understanding which human activities cause change in the demography and social structure of bird populations and how this change affects the probability these populations are likely to persist helps us develop effective management to mitigate human impacts. In central Florida, conspicuous human impacts on natural systems include residential development, citrus, forestry, grazing, military training, and human recreation. Our research has examined how these human activities affect two federally-listed birds: the Florida scrub-jay and the red-cockaded woodpecker.
Florida Scrub-jays. Florida scrub-jay populations are patchily distributed throughout their current range which is considerably smaller than their historic range. Over 30% of all scrub-jays occupy scrub habitats surrounded by suburbs and more than 60% occur in long-unburned scrubs. Our research focuses on population-specific demographic and life history patterns, dispersal patterns, immigration and emigration rates, and on developing stage-based individual and spatially-explicit population models that reflect habitat-specific life-history parameters. Since 1992, Reed Bowman and several interns and graduate students (see Student Research, page 30), have studied a banded population of scrub-jays in a suburban setting 8 km north of Archbold Biological Station. Demographic patterns suggest this population should be rapidly declining (l< 1): however, the population has remained relatively stable only because of frequent immigration. Our data suggest that these immigrants do not originate in native, undisturbed scrub; however it is unlikely that dispersal within suburbs could support the observed rates of immigration. We hypothesize that most immigrants are refugees from either destroyed habitat or habitat degraded by long-term fire suppression rather than from source populations in high-quality native habitat. We are developing a model in which long-term persistence of suburban jay populations depends on the duration of this immigrant pool which, in turn, depends on the amount of habitat at risk and the rate of habitat loss.
Of equal interest to these applied questions is understanding how demographic patterns influence scrub-jay social structure. Lower adult survival rates and the increased ability of jays to establish de novo territories in the suburbs results in greater breeding opportunities for non-breeding jays. As predicted by the habitat saturation model for the evolution of cooperative breeding, young scrub-jays in the suburbs often disperse and attempt to breed before they are one-year old, a relatively rare event in undisturbed habitat. Our continuing demographic studies will help us evaluate the relative fitness benefits of individuals adopting a "stay and help" strategy versus those that disperse and breed. Is the latter strategy more effective in a highly-disturbed ecological setting?
Dispersal is a critical parameter in spatially-explicit population models. At nearby Avon Park Air Force Range (APAFR), Bowman, Nathalie Hamel, and Larry Riopelle are examining scrub-jay dispersal patterns in a heterogenous landscape. Jays occur in a variety of landscape settings: 1) surrounded by open scrub saturated with other jay territories; 2) surrounded by open, non-scrub habitats without other scrub-jays; or 3) surrounded by dense, pine forests. Our demographic data suggest that production by scrub-jays surrounded by pine forests does not balance mortality. Dispersal of scrub-jays from these habitats follows suitable dispersal corridors. Scrub-jays from more open habitats, which tend to be demographic sources, are more likely to disperse randomly. However, they are not more likely to disperse farther nor cross greater non-scrub gaps than scrub-jays from territories surrounded by forest. What are the costs of moving through different habitats and does this influence dispersal patterns? A recently funded project will examine how different landscape mosaics influence the forays non-breeders make to assess breeding opportunities. By following radio-marked birds at APAFR, we can determine which habitats jays move through when off-territory and which habitats they avoid. At Cape Canaveral Air Station, Brevard County, Florida, Ted Stevens and Stephanie Legare are examining the response of scrub-jay demography and behavior to long-term fire suppression and a variety of different habitat restoration techniques. Together, these studies provide data on how scrub-jay populations respond to a variety of different human disturbances and insights into mitigating these impacts.
Red-cockaded Woodpeckers. Habitat loss and degradation has also increased fragmentation within and between red-cockaded woodpecker (RCW) populations in south and central Florida. Although most populations in this region are small (<25 breeding pairs) and relatively isolated (>30 mi from their nearest neighbor), many of these populations have remained relatively stable over the last few decades, notwithstanding declines directly related to habitat loss. Our research, led by Bowman, David Leonard, Leslie Backus, and Allison Mains, has focused on the demographic and behavioral characteristics of these small populations and how they relate to the community structure in a managed forest landscape. At APAFR, annual fledgling productivity is relatively low but adult survival is relatively high. As part of a year-long foraging behavior study, we determined that RCWs may compensate for the low density of pines in their territories by increasing territory size. On average, RCW territories at APAFR are 75% larger than those reported elsewhere. However, in a paper recently published in Molecular Ecology, Susan Haig, Bowman, and Tom Mullins reported that Fst values among south-central Florida populations, although still showing significant differentiation, were lower than elsewhere suggesting these populations have relatively high levels of gene flow. These results, coupled with our observations of frequent immigration into the APAFR population, suggest that the small and scattered RCW populations in south-central Florida may function as a metapopulation, thus according greater long-term stability than would be predicted for each individual population.
Lohrer, F.E . (Editor). 1998. Archbold Biological
Station, Biennial Report 1995-1996. Archbold Biological Station, Lake Placid. 62 pp.
© Archbold Biological Station, 1998, October.
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