Sibling competition affects nestling growth strategies in marsh tits

• 1. We manipulated the size hierarchy in broods of marsh tits (Parus palustris L.) by simulating hatching asynchrony to study how nestlings of different competitive ability, allocate their share of parental feedings to different growth strategies. 2. The mean rate of mass increase and the mass when the growth curve had reached an asymptote increased with the predicted competitive ability of nestlings. In contrast, rate of wing length increase was not related to overall competitive ability. The smallest nestlings in a brood even grew their wings significantly faster than the largest ones. 3. Nestlings that died due to sibling competition showed a steady reduction in the rate of mass increase compared to surviving nestlings from at least 6 days before death. Rate of wing length increase in these dying nestlings was, however, equal to surviving ones right until the last day before death. 4. Nest-leaving was initiated by the largest nestlings in a brood. When the process had started all nestlings left the nest in close succession with the result that the young/small nestlings had to leave at a younger age than their larger nestmates. 5. It seems as if individual nestlings are able to choose how to allocate resources to growth of the wing in relation to mass. In this way small nestlings are able to keep pace with their larger and older nestmates with respect to wing length. 6. The selective pressure responsible for the growth strategy of small nestlings may be the need to leave the nest together with their larger nestmates, which depends on their ability to fly and, thus, the development of the wing. 7. We suggest that sibling competition is one of the most powerful forces to explain intra-brood variation in growth and survival.

Ämnesord

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

Nyckelord

brood reduction

growth curve

hatching asynchrony

nest-leaving

Parus palustris

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