Mortality in Aransas-Wood Buffalo Whooping Cranes: Timing, location, and causes

Abstract

For long-lived species with low fecundity rates, population growth rate can be sensitive to changes in annual survival. Understanding where, when, and why animals die provides useful information for prioritizing conservation practices designed to increase survival. As part of a satellite tracking study, we identified 19 confirmed and suspected deaths of Whooping Cranes of various ages from the Aransas-Wood Buffalo Population. Of these, more occurred during winter (∼45%), compared with summer (∼40%) or migration (∼15%). Summer mortalities occurred exclusively within Wood Buffalo National Park, and all winter mortalities occurred on the primary wintering grounds along the Texas Gulf Coast. Predation was the most common cause identified; proximate cause of mortality was not known for most of the birds. Previous assessments of mortality, based on assumptions and some supporting data, speculated that most mortality occurred during migration. Although preliminary, our results are based on stronger evidence and provide a different perspective. Migration may be less risky than previously assumed and of similar risk to other seasons; thus, conservation or management efforts to reduce mortality may have greater effect when focused during breeding and wintering periods, although feasibility and efficacy of these actions will need to be determined.