Evaluating demographic habitat partitioning and its consequences during the non-breeding season in Loggerhead Shrikes

Abstract

The non-breeding season is an understudied, yet likely critical, period for many species. Understanding species’ resource requirements, and determining when limited resources and increased densities may lead to intraspecific competition and demographic partitioning, may aid species conservation efforts. Monitoring species’ resource requirements during the non-breeding season may be more important in highly modified ecosystems, such as intensive agricultural landscapes, where anthropogenic pressures may further limit resources. The Loggerhead Shrike ( Lanius ludovicianus ) is a rapidly declining avian species that winters in agricultural areas in the southeastern United States, but little is known about their ecology or potential demographic partitioning in this context. To fill these knowledge gaps, we compared multi-scale habitat selection, survival, and space use across age and sex classes of shrikes inhabiting an agricultural landscape in Arkansas, USA. We found that habitat selection differed among demographic classes. Specifically, females preferred areas with more fallow cover, utility wires, and anthropogenic perches, whereas males preferred areas with more agricultural fields and ditches and less soybean cover. However, overall, shrikes exhibited numerous similarities in habitat selection, generally preferring areas with greater developed land cover (within a predominantly agricultural landscape), greater water availability, and taller perches. Despite the observed variability in habitat selection, no differences in apparent seasonal and annual survival rates or home range size existed among groups. However, non-breeding dispersal distance between years differed by age class, with older individuals being more site faithful than younger individuals. We suggest that the demographic habitat partitioning we detected may reflect adaptive differential life history strategies associated with age and sex classes, but further study of habitat selection by Loggerhead Shrikes across seasons and habitat types will help clarify the variation, importance, and potential carry-over effects of non-breeding habitat partitioning.

Keywords

• agricultural landscape
• apparent survival
• habitat segregation
• habitat selection
• lanius ludovicianus
• non-breeding ecology
• site fidelity