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Detecting Mortality in Birds Following Release

Researchers at the University of Maine are researching the fundamental assumption of avian survival analysis; that the act of capture, handling, and marking birds does not affect subsequent survival. This assumption is violated if animals experience injury, physiological stress, or disorientation during capture and handling that increases their mortality risk following release. Such capture-related effects must be accounted for during analysis, typically by censoring individuals from the survival history, to avoid biasing the resulting survival estimates.

They reviewed studies of radio-marked upland game birds to characterize researcher approaches for addressing short-term effects of capture on survival, and used data from a study of Ruffed Grouse to illustrate an empirical approach for evaluating such effects and identifying time thresholds to censor birds that die shortly after release. A majority of studies (65 percent) reported using some form of censoring for mortality that occurred within one to three weeks after release, although only 8 percent of studies reported an empirical approach to identify a threshold for censorship. The researchers found that Ruffed Grouse mortality was greater from one to six days following release when compared with seven to 30 days.

NIFA supports this project through the McIntire-Stennis Capacity Grant Program.

Read the full article at Avian Conservation and Ecology.

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