Causes of Death of Female Cooper's Hawks from An Urban Setting in New Mexico, USA

Abstract

Knowledge of mortality factors affecting raptors is often based on opportunistically found carcasses. Some causes of mortality, however, are more likely to produce carcasses that will be discovered, thus opportunistic collections are biased. Studies of raptors tagged with transmitters can provide relatively unbiased cause-of-death information. We used data collected during 2011-2021 from 158 tagged female Cooper's Hawks (Accipiter cooperii) from an urban study area in New Mexico, USA to estimate the population-level effects of different causes of mortality. We used a multistate model to combine data from encounters of banded live and dead birds with data from transmitter-Tagged hawks to estimate annual age-specific survival rates. Cause-of-death information from the subset of tagged individuals was used to estimate proportions of first year (FY) and older (AFY) hawks that died annually from different causes. Most mortalities were caused by anthropogenic factors, especially collisions with human structures (e.g., windows, vehicles), which accounted for 45% (credible interval = 31%-60%) of FY deaths and 32% (18%-45%) of AFY deaths annually. From July 2020 to June 2021, purposeful killing by humans accounted for deaths of 17 (6-33) female Cooper's Hawks out of an estimated starting population of 216 (184-254). For both age classes, the ultimate cause of most deaths in late winter and early spring appeared to be associated with securing a nesting territory and mate. To our knowledge, this is the first study to provide relatively unbiased information on the importance of different causes of mortality for an urban raptor population.