Bobolink

Identificazione

Measurements:<p>Adults are 16–18 cm (6.3–7.1 in) long with short finch-like bills and weigh about 28 g (1 oz). Adult males are mostly black with creamy napes and white scapulars, lower backs, and rumps. Adult females are mostly light brown with black streaks on the back and flanks, and dark stripes on the head; their wings and tails are darker.

Tassonomia

Nome scientifico

Dolichonyx oryzivorus

Autorità

(Linnaeus, 1758)

Ordine

Passeriformi

Famiglia

Icteridae

Genere

Dolichonyx

Areale e habitat

The bobolink breeds in the summer in North America across much of southern Canada and the northern United States; from 1966 to 2015 the species experienced a greater than 1.5% annual population decrease throughout most of its breeding range, extending from the Midwestern United States to the Canadian Maritimes. The bobolink migrates long distances, wintering in southern South America. One bird was tracked migrating 12,000 mi (19,000 km) over the course of the year, often flying long distances up to 1,100 mi (1,800 km) in a single day, then stopping to recuperate for days or weeks.<p>Bobolinks often migrate in flocks, feeding on cultivated grains and rice, which leads to them being considered a pest by farmers in some areas. Although bobolinks migrate long distances, they have rarely been sighted in Europe — like many vagrants from the Americas, the majority of records are from the British Isles.<p>The species has been known in the southern United States as the "reedbird," or the "ricebird" from their consumption of large amounts of the grain from rice fields in South Carolina and the Gulf States during their southward migration in the fall. One of the species' main migration routes is through Jamaica, where they are called "butter-birds" and at least historically were collected as food, having fattened up on the aforementioned rice.<p>Bobolinks are the only species of land bird known to annually migrate through the Galápagos Islands, which are over 2,000 km from their primary migration route. A bobolink was collected in the Galápagos Islands by Charles Darwin in 1835. Bobolinks have been hypothesized to act as vectors for avian malaria-causing parasites arriving in the Islands. Additionally, bobolinks in the Galápagos have been found with seeds from Drymaria cordata, a plant native to the Galápagos but highly invasive elsewhere, entangled in their feathers, potentially spreading them to the mainland.

Areale riproduttivo

NA : s Canada and n USA

Areale non riproduttivo

c SA

Migrazione

Complete migrants

Comportamento

Their breeding habitats are open grassy fields, especially hay fields, across North America. In high-quality habitats, males are often polygynous. Females lay five to six eggs in a cup-shaped nest, which is always situated on the ground and is usually well-hidden in dense vegetation. Both parents feed the young.<p>Bobolinks forage on or near the ground and mainly eat seeds and insects. They are nicknamed the ".mw-parser-output .vanchor>:target~.vanchor-text{background-color:#b1d2ff}armyworm bird" because of their predation on large numbers of armyworms,: 453  including the true armyworm (Mythimna unipuncta) and the fall armyworm (Spodoptera frugiperda), acting as a natural pest control.: 453  In Florida, bobolinks feed most often on the Fall armyworm rather than the True armyworm, as the former is more common in the region.<p>Males sing bright, bubbly songs in flight.

Conservazione

During the 1800s the bobolink, like many birds, was slaughtered in large numbers for the meat trade.: 41 <p>The numbers of these birds are declining due to loss of habitat. Bobolinks are a species at risk in Nova Scotia, and throughout Canada. In Vermont, a 75% decline was noted between 1966 and 2007. Originally, they were found in tallgrass prairie and other open areas with dense grass. Although hay fields are suitable nesting habitats, fields which are harvested early, or at multiple times, in a season may not allow sufficient time for young birds to fledge. Delaying hay harvests by just 1.5 weeks can improve bobolink survival by 20%. This species increased in numbers when horses were the primary mode of transportation, requiring larger supplies of hay.<p>A 2021 study found that the reintroduction of American bison across the United States was detrimental to bobolink populations, with adult populations dropping as much as 62% and juvenile populations as much as 84%. This is presumed to be due to many new bison herds being managed more as livestock than wildlife, often kept in fenced pastures and protected from predation, which encourages overgrazing, trampling, and rapid multiplying. The study also found that lighter grazing by bison did not have the same harmful effects, demonstrating that the two species could likely coexist under the right circumstances.

Tendenza della popolazione

declining