Horned larks on the Tibetan Plateau adjust the breeding strategy according to the seasonal changes in the risk of nest predation and food availability

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Abstract

Songbirds in seasonal environments often adjust their breeding strategy according to spatial or temporal changes in breeding conditions. Here we investigate how horned larks Eremophila alpestris, a multi-brooded songbird on the Tibetan Plateau, responded to the changing risk of nest predation and food availability across breeding attempts. We showed that both nest concealment and food supply increased with plant growth, and horned larks adjusted their breeding strategies accordingly. First they selected nest-sites where predator density was low, which enhanced nest survival. Second, clutch size increased with improving breeding conditions. They did not adopt an ‘egg-size’ strategy as egg size did not change with laying sequence or breeding attempt. Instead, they adopted the ‘brood survival (feeding later-hatched nestlings more)’ and ‘brood reduction (feeding early-hatched nestlings more)’ strategies during early and later attempts. Moreover, nestlings’ growth varied with breeding attempt: more energy was invested into the growth of body mass during the first attempt but more energy was expended on the growth of linear structures during later attempts. This difference in energy allocation reflected changing food availability. We suggest that temporal changes of environmental factors are also the important force driving the evolution of avian breeding strategies.

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