and thus is not very likely to have rendered the region inhospitable to the merlin; global warming on the other hand cannot be dismissed as a reason, given that the merlin is essentially a subarctic species that barely ranges even into temperate climes. Also, it may be that the number of merlins wintering in the northern USA has increased during the 20th century.
Perhaps the most frequent cause of accidental death for individuals is collision with man-made objects, particularly during attacks. This may account for almost half of all premature deaths of merlins. In the 1960s and 1970s, organochlorine pesticides were responsible for declines—particularly in Canada—due to eggshell thinning and subsequent brood failure, and compromising the immune system of adults. This has since been remedied with restrictions on the use of DDT and similar chemicals, and numbers have rebounded. Overall, merlin stocks appear globally stable; while they may decline temporarily in places, they will usually increase again eventually, suggesting that this phenomenon is due to the fluctuations of supplementary food stocks discussed above.
- BirdLife International (2012). "Falco columbarius". IUCN Red List of Threatened Species. 2012. Retrieved 26 November 2013.old-form url
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- "Merlin". Audubon. 2014-11-13. Retrieved 2020-01-27.
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- Wink, Michael; Seibold, I.; Lotfikhah, F.; Bednarek, W. (1998). Chancellor, R.D.; Meyburg, B.-U.; Ferrero, J.J. (eds.). Molecular systematics of holarctic raptors (Order Falconiformes) (PDF). Holarctic Birds of Prey. Adenex & WWGBP. pp. 29–48.
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