Spring migration is winding down.\u00a0 The arrival of Blackpoll Warblers, Black-billed Cuckoos, Saltmarsh Sparrow and Nelson\u2019s Sparrow signifies the end of the spring spectacle.<\/p>\n
Having returned to Maine from the south, male birds are setting up territories and trying to attract a mate with songs and displays.\u00a0 We have a tendency to project an idyllic image of a happy bird couple raising a family.\u00a0 That image is often inaccurate.<\/p>\n
For starters, not every bird will be able to find a mate.\u00a0 Some of the best evidence for this statement comes from an experiment that was done in Maine over 50 years ago.\u00a0 The methodology of the study will be reprehensible to some.\u00a0 Nevertheless, we learned much from this experiment.<\/p>\n
The researchers mapped out a 40-acre forest plot.\u00a0 In early June, they determined that 154 territorial birds (males) were present.\u00a0 Then the removals began.\u00a0 The researchers shot as many of the singing males as they could.\u00a0 Within two weeks, the density of male birds was reduced to 21% and kept at that level until July 11. By July 11, 528 adult birds had been killed.\u00a0 That\u2019s 3.5 times the original density of birds!<\/p>\n
This removal experiment tells us there are lots of unmated males that are lurking around, hoping for a chance to acquire a territory and a mate.\u00a0 These non-territorial birds are called satellite males in the ornithological literature.\u00a0 The experiment shows that there must be many satellite males waiting for an opportunity.<\/p>\n
As in mammals, birds show a 50:50 proportion of females:males.\u00a0 With so many satellite males, there must be unmated females present as well who never come into the vicinity of an unmated male.\u00a0 The failure of some birds to find a mate challenges our fanciful notion of wedded bliss in birds.<\/p>\n
An even greater challenge to that notion lies in the fact that avian social life has soap opera aspects.\u00a0 Cheating on a mate occurs frequently.\u00a0 Thanks to the development of DNA fingerprinting techniques, we can determine the paternity of nestlings.\u00a0 Although 90% of bird species are classified as monogamous, 30% of nestlings are sired by a male other than the female\u2019s mate.<\/p>\n
It\u2019s a two-way street.\u00a0 Females seek multiple partners to fertilize their eggs and males seek as many female partners outside of the pair-bond as they can find.\u00a0 These dalliances are referred to as extra-pair copulations and their importance in the field is indicated by the fact that every ornithologist knows the initialized version, EPC, of this behavior.<\/p>\n
The male incentive for EPCs is clear: to father as many baby birds as possible.\u00a0 What\u2019s the advantage for a female who can produce only a few eggs?\u00a0 The best argument is that the female is seeking to increase the variability of her nestlings.\u00a0 The environment is always changing and having greater variation in her offspring increases the chances that one or two of those offspring will better fit the demands of the environment in the future.<\/p>\n
The reproductive life of a territorial male is pretty good.\u00a0 He fathers at least some of the eggs laid by his mate and perhaps has some EPCs with females on neighboring territories.\u00a0 But what about those unmated satellite males?\u00a0 Do they get to reproduce at all?\u00a0 Satellite males do not have a territory because they are outcompeted by the stronger males who can defend a territory.\u00a0 Weaker males are usually younger as well.<\/p>\n
Some males engage in a type of trickery called delayed plumage maturation.\u00a0 In the second year of their life, their plumage resembles that of a female.\u00a0 This disguise allows them to slip into the territory of a male (he\u2019s got cheating on his mind) and sneak a quick mating with the resident female.\u00a0 Check your field guide to see the second-year plumage of American Redstarts, Baltimore Orioles and Red-winged Blackbirds.<\/p>\n
[Originally published on May 25, 2014]<\/p>\n\n
Spring migration is winding down.\u00a0 The arrival of Blackpoll Warblers, Black-billed Cuckoos, Saltmarsh Sparrow and Nelson\u2019s Sparrow signifies the end of the spring spectacle. Having returned to Maine from the south, male birds are setting up territories and trying to attract a mate with songs and displays.\u00a0 We have a tendency to project an idyllic […]<\/p>\n","protected":false},"author":146,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_s2mail":"yes","ngg_post_thumbnail":0,"footnotes":""},"categories":[4625,433],"tags":[],"builder_content":"","_links":{"self":[{"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/posts\/667"}],"collection":[{"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/users\/146"}],"replies":[{"embeddable":true,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/comments?post=667"}],"version-history":[{"count":1,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/posts\/667\/revisions"}],"predecessor-version":[{"id":669,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/posts\/667\/revisions\/669"}],"wp:attachment":[{"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/media?parent=667"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/categories?post=667"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/tags?post=667"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}