スミソニアン国立動物園さんのインスタグラム写真 - (スミソニアン国立動物園Instagram)「🐦Get out and stay out! #KirtlandsWarblers have finally kicked brown-headed cowbirds out of their 🐣 nests in #Michigan, where they breed. For the past 40 years, brown-headed cowbirds have been trapped and killed in Michigan to prevent them from laying eggs in endangered Kirtland’s warbler nests—causing warbler parents to care for cowbird chicks instead of their own chicks. A study by scientists from the Smithsonian Migratory Bird Center and Utah State University found that Kirtland’s warblers may no longer need the extra protection against parasitic brown-headed cowbirds. In 2018, cowbirds parasitized less than 1% of Kirtland’s warbler nests in Michigan after scientists gradually removed cowbird traps during the previous three nesting seasons. From 2015 to 2018, researchers found only 20 cowbirds during surveys in the warblers’ core breeding range in Michigan. During those four nesting seasons, only four of 514 Kirtland’s warblers’ nests were parasitized by cowbirds. Initially in 2015 and 2016, scientists closed 12 cowbird traps at four study sites. Seven additional traps were closed in 2017. Finally, in 2018 researchers closed all of the traps across the entire core breeding range in Michigan. Kirtland’s warblers became dependent on conservation efforts in Michigan, which is where their summer nesting grounds are, in 1972. Although cowbirds are a native species to North America, they had not lived in Michigan before the early 1900s. By 1971, only 200 male Kirtland’s warblers remained in the wild and about 70% of their nests were parasitized by cowbirds. There are now 2,300 breeding male Kirtland’s warblers and the number of cowbirds in Michigan is decreasing, not due to trapping, but more likely because of changes to the surrounding landscape. Northern Michigan is now much more forested than it was in 1972, due to reversion of lands from agriculture to forested habitats. Cowbirds do not like to live in forests and prefer open landscape, or landscapes that have been cleared for agriculture. #WeSaveSpecies #Ornithology」11月23日 1時30分