![]() North American songbird ranges are also not limited by flight ability: migratory birds that can fly efficiently are not necessarily better at expanding their ranges than non-migratory birds in this region. Other factors, such as the availability of each species’ preferred habitat, may be responsible for variation in range size. Their results did not support either hypothesis: within North American songbirds, migratory behavior is providing neither an opportunity nor a limit when it comes to range size. With the help of U-M Undergraduate Research Opportunity Program (UROP) students Vera Ting and Charles Kotila, they used the collection of North American birds at the U-M Museum of Zoology to measure wing shape, a proxy of flight ability, on over 1000 specimens to assess whether the high flight ability of migratory birds allows them to expand their ranges more than other species. ![]() To test their hypotheses, the researchers analyzed the effect of seasonal migration, including the distance of migration, on breeding range size and on how much of each species’ climatically suitable habitat was covered by its range. These limitations may select against individuals that explore new regions, reducing range expansion.” Even though long-distance migratory birds can fly well, they don’t actually have the flexibility to fly everywhere due to the time limitations associated with migration and dangers of straying from the migratory route. “The second hypothesis predicts the opposite: smaller ranges for long-distance migrants, with suitable breeding areas potentially left unoccupied. ![]() By contrast, migratory birds can fly almost anywhere, so their breeding ranges could encompass all regions with suitable habitat for them. Many species of animals, including poorly-flying birds in the tropics, are restricted to particular regions by their “dispersal ability”: they might not be able to cross mountains or rivers, for example, even if there is a suitable place to breed on the other side. “The first hypothesis predicts that migratory birds should have very large breeding ranges. These different aspects of migration have led to two hypotheses for the effect of seasonal migration on range size: ![]() “On the other hand, seasonal migration also has a slim margin of error: failure to follow strict timing and routes in migration can lead to disaster for birds because of the consequences of ending up too far north when a snow storm comes, or too far over the ocean when running out of energy. “Seasonal migration is associated with tremendous flight ability, which may give migratory birds opportunities that other species lack (such as the ability to cross oceans or mountains),” said Pegan. Teresa Pegan, a graduate student in ecology and evolutionary biology and her advisor, Professor Benjamin Winger, published “ The influence of seasonal migration on range size in temperate North American passerines.” Ecotoxicology DOI 10.1007/s10645-2.A new study published in May 2020 in Ecography asks whether seasonal migration influences breeding range size in North American songbirds. A preliminary assessment of mercury in the feathers of migratory songbirds breeding in the North American subarctic. Further examination would prove useful in clarifying mercury exposure and ecological relationships in this under-studied region. Overall, however, the degree of mercury exposure observed was low for songbirds breeding in the subarctic. There was an indication that mercury concentrations of breeding songbirds may vary by diet composition, with non-invertivorous species possibly tending towards lower mercury concentrations. Most species sampled showed relatively low mercury, but some individuals had high enough concentrations to be subject to adverse physiological and behavioral effects. In this limited sample of songbird feathers, mercury concentrations ranged from near zero to 6.34 μg/g. Mercury levels found in feathers indicates exposure during the period of feather growth, which we assume largely took place on the breeding ground. Overall, we analyzed 343 feather samples collected in 2015–2017 for their total mercury content. In this preliminary study, we examined mercury exposure in 12 migratory songbird species breeding in Denali National Park & Preserve, in subarctic interior Alaska. Passerines appear to have a greater sensitivity to mercury than other avian orders, and little data exists for mercury exposure in songbirds breeding at high latitudes. A preliminary assessment of mercury in the feathers of migratory songbirds breeding in the North American subarctic Abstract
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