Black Oystercatcher, Avila Beach, CA скачать в хорошем качестве

Black Oystercatcher, Avila Beach, CA

Black Oystercatcher, Avila Beach, CA April 29, 2025 Pair of Black Oystercatchers constructing nest bowl on traditional nest rock by the Cal Poly Pier in Avila Beach, CA "Bird of the World" Nest Site: Selection Process Pairs consistently used same nest bowl 3 yr in Alaska and more than 5 yr in California . Sometime make multiple nests; female chooses in which one to lay . Breeding pairs appear to select territories that combine an appropriate nest site, usually located above highest high-tide level, with adequate foraging areas. Microhabitat And Site Characteristics Uses a variety of nest sites: sand and pebble beaches, shell beaches, cobble beaches, gravel outwashes, exposed rocky shorelines, wave-cut platforms, and offshore boulders. Eggs in successful nests are more similar to substrate (in particle size) than are eggs in failed nests. Pairs generally avoid placing nest in vegetation; place beach nests to shore side of vegetation line. Substrate around nest site has sparse to no erect vegetation. Incubating bird's view is often obstructed more than 180° by vegetation or rock. Lower peripheral view may also be obstructed. Nest: Construction Process Birds toss rock flakes, pebbles, or shell fragments toward nest bowl with a sideward and backward flick of bill; occasionally carry flakes and toss them forward from bill. Intermittent nest construction begins 2–3 wk before eggs are laid; can be accomplished in less than 1 hour. Male and female both participate in nest-building, but male does most of it. Female assumes increased role during incubation. Nest-building only occurs when both mates are present and may strengthen pair bond. Nest bowl is made by pressing chest into nest material or fine-grained sediments. Like American Oystercatcher, Black Oystercatcher may use feet to excavate scrape in sand or sod. Antagonistic interactions, usually initiated by male, are directed toward other Black Oystercatchers during prenesting. Nest Structure And Composition Matter Variable. Ranges from bare rock or sod to a structure composed of hundreds of rock flakes and shell fragments. Most often consists of mixture of rock flakes and shell fragments. Less fabricated structure on sand/pebble or cobble beaches than on rock outcroppings. Nest Dimensions Extremely variable. Average nest diameter on Destruction I., WA, 20.5 cm; average depth 2.8 cm. Deeper nests tend to be more successful. Microclimate No specific information. Although Black Oystercatchers breed along rainy and windy coastlines, nests provide little protection from environment. Mounding of rock flakes for nests placed on impervious rock substrates may elevate eggs above pools caused by frequent summer rains. Nests placed behind vegetation clump, log, or rock may reduce exposure to wind or visual predators. Maintenance Of Nests, Nonbreeding Nests Multiple nests, or scrapes, are made each season and accumulate in territory over time. Renesting females use same nest or lay in different one. Highly constructed nests on rock outcroppings are often used in subsequent years.