The influence of landscape composition and configuration on breeding waterfowl pair abundance in Wisconsin

Abstract

Habitat loss and fragmentation have negatively impacted breeding birds across the world. Across guilds, grassland-dependent birds have experienced the largest proportional loss of their breeding population while wetland-dependent birds have realized overall net gains in part due to focused conservation efforts. However, some species within the wetland-dependent guild have a strong dependence on non-wetland land cover types during the annual cycle and therefore may be equally sensitive to reductions in the composition and altered configuration of upland landcover, such as grasslands. We explored the influence of landcover composition and configuration on the number of breeding pairs of a breeding habitat generalist, the mallard (Anas platyrhynchos), and a grassland-dependent breeding species, the blue-winged teal (Spatula discors), in agriculturally-intensive landscapes of Wisconsin, USA. Because of the extensive landscape alteration and habitat fragmentation that has occurred, we expected mallards to have a more utilitarian response to varying landscape composition compared to a grassland nesting obligate like blue-winged teal. We used helicopter surveys conducted across 8 years (2001–2003, 2006–2009, and 2012) and remotely-sensed land cover data to investigate the influence of habitat associations on relative abundance of breeding pairs. Model selection indicated that landscape composition models outperformed landscape configuration and null models for both species. Consistent with our predictions, we found that mallard pair counts were positively influenced by a greater number of land cover covariates compared to blue-winged teal. Both blue-winged teal and mallard breeding pairs were positively related to increased composition of emergent and scrub-shrub wetlands as well as upland grassland. Additionally, we found that mallard pairs were positively related to forested, cattail (Typha sp.), and open water wetland types, whereas predicted blue-winged teal pair abundance was negatively related to forested wetlands and had a nonlinear relationship and declined when surveyed land sections were comprised of more than 30% cattail-dominated wetlands and 20% open-water wetlands. Increased quantities of cattail-dominated and open-water wetland cover types comparatively provide less habitat for blue-winged teal and may reflect broader shifts in habitat composition that have likely resulted from agricultural intensification and stabilized hydrology. Conservation activities that preserve existing nesting land cover types or restore hydrologically-dynamic emergent wetlands in proximity to upland grassland cover could mutually benefit both species.