Integrating citizen-science data with movement models to estimate the size of a migratory golden eagle population

Abstract

a b s t r a c tEstimating population size is fundamental to conservation and management. Population size is typically estimated using survey data, computer models, or both. Some of the most extensive and often least expensive survey data are those collected by citizen-scientists. A challenge to citizen-scientists is that the vagility of many organisms can complicate data collection. As a result, animal-movement effects on data collection can adversely affect modeling of those data. Thus, it would be helpful to develop methods that integrate citizen-science datasets with models that account for animal movement. We used hawk-count data collected by citizen-scientists to estimate the number of golden eagles (Aquila chrysaetos canadensis) migrating through Pennsylvania, USA. To do this, we designed a computer model to simulate migratory flights of eagles to estimate what proportion of the population is available (i.e., within visible range or close enough) to be counted at hawk-count sites in Pennsylvania. We then conducted a multi-state mark-recapture analysis to estimate detection probability (i.e., the rate at which birds within visible range are observed) of migrating eagles. Finally, we used availability rates and detection probabilities to adjust raw hawk-count data to produce estimates of population size. Our models suggest that 24% (±14; mean ± SE) of migrating golden eagles are available to be counted at hawk-count sites, and that 55% (±1.6) of the available eagles are detected by hawk-count observers. We estimate that 5122 (±1338) golden eagles migrate annually through Pennsylvania. Our analysis provides the first quantitative estimate of the size of the eastern golden eagle population, and we demonstrate the utility of one approach to use citizen-science data to address a pressing conservation goal-population size estimation.

Spatial and temporal patterns in age structure of Golden Eagles wintering in eastern North America

“…Other factors may have also contributed to the absence of latitudinal segregation in our study. Given the somewhat large scale of movements of eastern Golden Eagles during winter (Miller et al ) and their low population density (Dennhardt et al ), high‐quality habitat and food may be available across their winter range. If so, this distribution of resources may reduce competition and explain the lack of age structure in wintering areas.…”

Multi‐state open robust design applied to opportunistic data reveals dynamics of wide‐ranging taxa: the sperm whale case

“…The substantial advantage of this method is in its ability to estimate the size and various parameters describing the inter-and intra-annual dynamics of populations with imperfect detectability. We believe MSORD models could provide relevant information on the demography of many wide-ranging species where data are regularly collected by the public through ecotourism activities (Davies et al 2012, Dennhardt et al 2015, Bertulli et al 2017). We do not advocate that opportunistic data could or should replace data collection under well-designed CMR studies.…”

Wintering Golden Eagles on the coastal plain of South Carolina

“…Golden Eagles are rare winter residents in eastern North America, with most occurring at higher elevations along the Appalachian Mountains and others at lower elevations elsewhere (Millsap andVana 1984, Dennhardt et al 2015). Golden Eagles in the east are highly migratory and migrant populations have re-cently been estimated at 5000 individuals along the Appalachian migration corridor (Dennhardt et al 2015). Little is known about the winter ecology of Golden Eagles in the east (Katzner et al 2012, Dennhardt et al 2015, but recently developed technologies have enhanced our ability to address this information gap.…”