Furthermore, fall nesting is likely to have been underreported in the literature. Among North American terrestrial birds in general, fall breeding has been reported in 16% of all species and is significantly more common among residents and colonially nesting species, in which the frequency exceeds 25%. Ecologically, fall nesting is closely tied to the acorn crop and thus to breeding success in the following, rather than the prior, spring. Fall nesting is less likely in groups in which either the male or female breeding adults have undergone a change from the prior year, but groups are otherwise indistinguishable. ![]() ![]() Fledglings from fall nests constitute 4.3% of the population's total productivity and survive and recruit to the population at levels comparable to spring fledglings. Fall nests occur in about one-third of all years, taking place when the acorn crop is large and summer temperatures are relatively high. These latter nests are mostly initiated in late summer but often do not fledge until at least late September and are thus referred to here as ‘fall’ nests. One peak occurs in spring during which the majority of breeding takes place, while a second is centered in late August as the new acorn crop matures. ![]() Acorn Woodpeckers ( Melanerpes formicivorus) at Hastings Reservation in central coastal California exhibit a bimodal peak in annual breeding activity.
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