08 December 2009

Types of Nests

SCRAPES--shorebirds, terns, skimmers, & nighthawks use scrapes in open situations.

BURROWS-- birds probably used natural burrows and later moved to excavated burrows. Advantages of ground burrows include: microclimate stable, nest stable, predator protection. Disadvantages are that predators, once they find them, can easily get at them. On the other hand, birds in tree burrows escape flooding. But they have disadvantages. They must compete for tree holes. It takes time to make both kinds of burrows. Hole nesters usually enjoy a 66% success rate in fledging whereas open cup nesters have only a 55% rate.

PLATFORM NESTS--primitive: line scrape with vegetation or, in the case of waterfowl, line nests with own feathers. Cormorants and herons build platforms in trees. Grebes build floating platforms, anchored to vegetation. One South American coot, Horned Coot, piles pebbles and makes own island for its terrestrial platform nest (over years, pebbles can weigh up to ton).

CUP NEST--probably evolved from platform nest, most common today. Robin = statant nest, support mainly from below. Barn Swallow = adherent nest, stuck on side. Swifts use saliva to glue nests to edges of chimneys. Ovenbirds build cup on ground. Marsh Wrens make a ball entered by small hole. Other "cups" are suspended from top by branches vireos from rims at tree forks = pensile nests. Finally, orioles = pendulous nests, that hang from branches.

COMMUNAL NESTS--some weavers basically build apartment houses (look for a picture on the Internet).

(Mention should be made of Smooth-billed Ani: they lay their eggs in each other's nests = a step towards parasitism? Each nest is separate though.)

Black-tailed Gnatcatcher

1 comment:

  1. with smooth billed anis, thew female would often throw out the older eggs of other females and lay her new eggs.