Abstract
ABSTRACT Changes in autumn raptor migration phenology have been documented at hawk count sites across North America. Delays in autumn migration are the most common shift reported, but these changes vary by species. We examined autumn raptor phenology and changes in count effort for 14 raptor species over 46 yr at Hawk Ridge in Duluth, Minnesota, USA, using mean passage date. Among the 14 raptors, six species showed significant shifts in migration phenology; four toward later migration and two toward earlier migration. Our results suggest fewer species are shifting toward later phenology than previously reported at Hawk Ridge and that some previously reported changes in phenology may be explained by changes in survey effort. This study highlights the importance of controlling for count effort when analyzing migration phenology, emphasizing the need for consistent effort in the future.
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