Changes in climate and land use interact to create an ecological trap in a migratory species
This project evaluated the relative contribution of climatic and land-use factors on northern pintail demographic performance across the PPR. The authors used pintail counts from annual Waterfowl Breeding Population and Habitat Surveys (BPOP) from 1958–2011 to separate count data into a demographic process and a habitat selection process using a hierarchical model for 24 BPOP strata in the PPR. This novel approach provides an alternative way of identifying ecological traps in the absence of individual survival and fitness and accounts for the indirect pathways by which climate and agriculture impact pintail through their influence on wetland availability. Decoupling these processes identified an ecological trap related to increasing cropland land cover where pintail selected for cropland relative to its availability but demographically performed poorly.
On average, the mean expected population growth rate over the duration of the study period was negative for strata in Canada and positive for strata in the US. Several strata were identified where this ecological trap is contributing significantly to mismatches between habitat selection and demographic processes. These areas, all located in Canada (southern Alberta, western and northeast Saskatchewan), are attracting an increasingly greater number of pintail than expected given demographic processes, thereby acting as strong ecological traps and essentially serving as pintail “sinks”. However, in portions of the U.S. (central and western North Dakota) pintails are settling at higher rates than expected in areas where demographic processes yield positive growth rates, effectively serving as pintail “sources” that help offset the vast areas of the Canadian PPR where pintail abundance is declining.
Results from this project clearly suggest that investments in conservation programs and agriculture practices (e.g., winter wheat) which limit nest destruction could be important for improving pintail population growth. For the U.S., this research also provides ancillary support for the benefits of private lands conservation, grassland and wetland easements, and USDA Farm Bill Programs - particularly CRP - in the PPJV to sustaining continental pintail populations. Thus, this research reflects positively on the successful conservation efforts and programs of the PPJV partnership. Funding for this research was supported by PPJV partners including Delta Waterfowl Foundation and the James C. Kennedy Endowment for Wetland and Waterfowl Conservation at Colorado State University.
The full paper is available online.