Using species distribution models to define nesting habitat of the eastern metapopulation of double‐crested cormorants

Abstract

When organisms with similar phenotypes have conflicting management and conservation initiatives, approaches are needed to differentiate among subpopulations or discrete groups. For example, the eastern metapopulation of the double‐crested cormorant (Phalacrocorax auritus) has a migratory phenotype that is culled because they are viewed as a threat to commercial and natural resources, whereas resident birds are targeted for conservation. Understanding the distinct breeding habitats of resident versus migratory cormorants would aid in identification and management decisions. Here, we use species distribution models (SDM: Maxent) of cormorant nesting habitat to examine the eastern P. auritus metapopulation and the predicted breeding sites of its phenotypes. We then estimate the phenotypic identity of breeding colonies of cormorants where management plans are being developed. We transferred SDMs trained on data from resident bird colonies in Florida and migratory bird colonies in Minnesota to South Carolina in an effort to identify the phenotype of breeding cormorants there based on the local landscape characteristics. Nesting habitat characteristics of cormorant colonies in South Carolina more closely resembled those of the Florida phenotype than those of birds of the Minnesota phenotype. The presence of the resident phenotype in summer suggests that migratory and resident cormorants will co‐occur in South Carolina in winter. Thus, there is an opportunity for separate management strategies for the two phenotypes in that state. We found differences in nesting habitat characteristics that could be used to refine management strategies and reduce human conflicts with abundant winter migrants and, at the same time, conserve less common colonies of resident cormorants. The models we use here show potential for advancing the study of geographically overlapping phenotypes with differing conservation and management priorities.

Migratory Flyways May Affect Population Structure in Double‐Crested Cormorants

“…Our results also imply that the apparent line of demarcation between the 2 populations cuts across subspecies designations. The geographic designations that follow Dorst and Mougin (1979) and Watson et al (1991) suggest that the cormorants breeding in Arkansas, Mississippi, and Alabama could be from expansions of the P. a. floridanus range (Sheehan et al 2017), whereas our samples suggest they are not distinct from cormorants originating from Minnesota, Michigan, New York, and Vermont, and therefore are more likely from the P. a. auritus population (both subspecies are referred to by the same common name). Further, we collected samples from both wintering flocks (putatively P. a. auritus ) and breeding colonies (putatively P. a. floridanus ) in Mississippi and for the first time in Alabama (Fig.…”

“…These conflicts, particularly with respect to commercial and natural resources such as aquaculture and sport fisheries, have resulted in often‐controversial management of cormorants as a nuisance wildlife species (Dorr and Fielder 2017). One question central to this contentious issue is whether cormorants should be classified into subspecies, and, if so, how those subspecies should be regulated and managed (Mercer et al 2013, Sheehan et al 2017).…”

Heronry distribution and site preference dynamics of tree-nesting colonial waterbirds in Tamil Nadu

“…The site-level variables required to understand the nesting ecology of waterbirds have still not been studied in depth (Kreakie, Fan & Keitt, 2012); parameters that could influence nesting include water depth, disturbance level, vegetation, distance from roads and settlements and water quality etc. (Maleki et al, 2016;Sheehan et al, 2017). Other landscape complexities that may also influence the nesting sites of these birds need to be identified and considered in future models.…”

Nesting habitat suitability and breeding of Asian woollyneck (Ciconia episcopus) in Nepal

“…In such situations, focused or opportunistic data collection can be used to identify local factors that can be included in predictive habitat distribution models, which in turn help ecologists or conservation practitioners identify potential new areas for future surveys. Such an approach has been effectively used for avian nesting habitat predictions in double-crested cormorants Phalacrocorax auratus (Sheehan et al 2017 ) and red-crowned crane Grus japonensis (Wu et al 2016 ) .…”