Abstract
In altricial birds, energy supply during growth is a major predictor of the physical condition and survival prospects of fledglings. A number of experimental studies have shown that nestling body mass and wing length can vary with particular extrinsic factors, but between-year observational data on this topic are scarce. Based on a seven-year observational study in a central European Tengmalm’s owl population we examine the effect of year, brood size, hatching order, and sex on nestling body mass and wing length, as well as the effect of prey abundance on parameters of growth curve. We found that nestling body mass varied among years, and parameters of growth curve, i.e. growth rate and inflection point in particular, increased with increasing abundance of the owl’s main prey (Apodemus mice, Microtus voles), and pooled prey abundance (Apodemus mice, Microtus voles, and Sorex shrews). Furthermore, nestling body mass varied with hatching order and between sexes being larger for females and for the first-hatched brood mates. Brood size had no effect on nestling body mass. Simultaneously, we found no effect of year, brood size, hatching order, or sex on the wing length of nestlings. Our findings suggest that in this temperate owl population, nestling body mass is more sensitive to prey abundance than is wing length. The latter is probably more limited by the physiology of the species.
Highlights
In altricial birds, phenotypic characteristics of nestlings such as body mass and wing length can affect sibling competition [1,2], nestlings’ survival [3,4] and at which age each individual fledges [5]
The body condition of Montagu’s harrier Circus pygargus fledglings does not vary according to sex and food abundance [30], the larger sex of marsh harrier Circus aeruginosus nestlings has no reduction effect on the smaller sex [28], and brood size in common grackles Quiscalus quiscula has no effect on nestling body mass [31]
We found that nestling body mass, controlled for age, significantly varied among study years, hatching order groups and sexes (Table 2)
Summary
Phenotypic characteristics of nestlings such as body mass and wing length can affect sibling competition [1,2], nestlings’ survival [3,4] and at which age each individual fledges [5]. Factors Affecting Growth of Tengmalm's Owl changes in food supply, the youngest nestling usually dies first due to its poor body condition (i.e. brood reduction theory; [16,17,18,19,20]). This effect is more pronounced during food scarcity [16,19,21]. Despite the reasonable amount of existing experimental studies on the differential quantity and quality of fledglings, observational studies remain scarce
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