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At least 217 records · Page 12Linked to original sources
USGS1998

Elemental contaminants in the livers and ingesta of four subpopulations of the American coot (Fulica americana): An herbivorous winter migrant in San Francisco Bay

Water birds with diets high in animal foods in the San Francisco Bay area are exposed to trace elements that are potentially health impairing. Water birds with herbivorous diets have been less thoroughly examined. The concentrations of trace elements in the livers and the esophageal contents of an herbivorous water bird, the American coot ( Fulica americana ) were measured to compare levels of contaminant exposure among different locations in the Bay system and with other water birds. A total of 39 coots were collected from four sites: Napa River and Mare Island Strait in the north, Berkeley in the middle, and Coyote Creek in the south. Livers of Berkeley samples differed significantly from those of Napa River and Mare Island Strait by their greater concentrations of As and B and lower concentrations of Cu, but they seemed to be within normal ranges for birds. Otherwise the concentrations of trace elements in the livers did not differ among sites. Ingesta samples from Berkeley differed from the other sites because they tended to be higher in Al, V, and Zn. In contrast to waterfowl, livers from the herbivorous coots in San Francisco Bay showed little exposure to Cd, Hg, Pb, or Se. Coot ingesta showed few samples with measurable levels of Cd, Hg, or Se and had low levels of Pb. The herbivorous diet of coots may shield them from exposure to such elements. However, high levels of V were present in coot livers and ingesta from all four sites, suggesting adaptation to this toxic element.

California↗
USGS1995

Breeding productivity and adult survival in nongame birds

Populations of many North American land-birds, including forest-inhabiting species that winter in the Neotropics, seem to be declining (Robbins et al. 1989; Terborgh 1989). These declines have been identified through broad-scale, long-term survey programs that identify changes in abundance pf species, but provide little information about causes of changes in abundance or the health of specific populations in different geographic locations. Population health is a measure of a population's ability to sustain itself over time as determined by the balance between birth and death rates. Indices of population size do not always provide an accurate measure of population health because population size can be maintained in unhealthy populations by immigration of recruits from health populations (Pulliam 1988). Poor population health across many populations in a species eventually results in the decline of that species. Early detection of population declines allows managers to correct problems before they are critical and widespread. Demographic data (breeding productivity and adult survival) provide the kind of early warning signal that allows detection of unhealthy populations in terms of productivity or survival problems (Martin and Guepel 1993). In addition, demographic data can help determine whether population declines are the result of low breeding productivity or low survival in migration or winter. Breeding productivity data also can help identify habitat conditions associated with successful and failed breeding attempts. Such information is critical for developing habitat- and land-management practices (Martin 1992). Here, we provide examples of the kinds of information that can be obtained by broad-scale demographic studies.

Book chapter↗
USGS2004

Estimating population trends with a linear model: Technical comments

Controversy has sometimes arisen over whether there is a need to accommodate the limitations of survey design in estimating population change from the count data collected in bird surveys. Analyses of surveys such as the North American Breeding Bird Survey (BBS) can be quite complex; it is natural to ask if the complexity is necessary, or whether the statisticians have run amok. Bart et al. (2003) propose a very simple analysis involving nothing more complicated than simple linear regression, and contrast their approach with model-based procedures. We review the assumptions implicit to their proposed method, and document that these assumptions are unlikely to be valid for surveys such as the BBS. One fundamental limitation of a purely design-based approach is the absence of controls for factors that influence detection of birds at survey sites. We show that failure to model observer effects in survey data leads to substantial bias in estimation of population trends from BBS data for the 20 species that Bart et al. (2003) used as the basis of their simulations. Finally, we note that the simulations presented in Bart et al. (2003) do not provide a useful evaluation of their proposed method, nor do they provide a valid comparison to the estimating- equations alternative they consider.

Condor↗