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Variation in the wing patches of juvenile Black-billed Magpie Pica pica

100%

Reed L. M., Wang X., Trost C. H.

Acta Ornithologica

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1997

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tom 32

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nr 1

93-97

Variability in morphological features is one mechanism by which recognition of individuals or kin, crucial to many social interactions, can occur. Patches in the remiges of magpie wings (white patches with black tips) contain information regarding the bearer's age and sex. Juvenile wing patches of both Black-billed Pica pica hudsonia and Yellow-billed Magpies Pica nuttalli contain between 10 to 12 feathers with variable lengths of white. Our investigations examine the relationship between wing patch morphology and relatedness. We measured the black tips on the primaries of one wing on 29 fledglings from seven nests. We derived a discriminant function based on the length of black on three inner primaries that successfully assigned 75 % of the birds to their natal nests (random assignment = 14% correct). We also compared the total length of black tips in the wing patches of young from 33 nests. We found less variation in the patch size within than between nests (log transformed ANOVA F = 8.339, p < 0.001; Kruskal-Wallis H = 113.6, p < 0.001). These results suggest that familial resemblance is encoded in juvenal magpie wing patches. Family recognition may be important both to the parents, who provide protection and food for their young, as well as between siblings, who apparently know each other.

2

Advantages of early versus late nesting in Black-billed Magpies Pica pica hudsonia variation in productivity, sex ratio, and fledgling size

100%

Gersteli A. T., Trost C. H.

Acta Ornithologica

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1997

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tom 32

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nr 1

39-44

Studies of Black-billed Magpies Pica pica hudsonia in Idaho, USA showed greater reproductive success in early nests. Overall, offspring from early nests were larger in body size and had longer bill lengths, both characteristics associated with social dominance in the non-breeding flock. Preliminary determination of the sex of nestlings shows: 1) a disproportionate number of male nestlings in early nests; 2) both male and female nestlings are heavier in early nests than later nests; and 3) in contrast, bill lengths are greater in early males but early and late females have the same bill length. Females in our study area do not use their bills in social displays. The anatomical traits of males from early nests are associated with higher social status and thus higher eventual nesting success. This indicates that even as nestlings, Magpies acquire physical characteristics related to social status and eventual probability of breeding. We are currently unable to determine if this is due to differential parental investment throughout the nesting period, or whether it is due to differing environmental effects within early and late nesting periods.

3

The effect of sibling competition on the subsequent social status of juvenile North American Black-billed Magpies Pica pica hudsonia

80%

Trost C. H., Webb C. L.

Acta Ornithologica

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1997

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tom 32

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nr 1

111-119

Hatching asynchrony results in competition between the nestling Black-billed Magpies Pica pica hudsonia and is of interest because long-lasting social ranks are probably initiated during the nestling and fledgling stages. The first-hatched birds grow at a significantly faster rate than their day-2 siblings. Flocks of young males and separate flocks of young females were held in an aviary until their dominance relations were known. Strictly linear hierarchies were quickly established among the young males, but females did not exhibit linear hierarchies. The only morphological correlate with dominance was bill length, and then only in the males. During the course of two years brother pairs were entered together into an aviary flock of five or more wild caught, non-sibling hatching year (HY) males. Supplantings were scored until a linear dominance hierarchy was compiled. Most males who were heavier at fledging were also dominant to their smaller brother(s) four to eight months later. It is concluded that the relative nest rank (i.e. hatching order and fledging weight) affects dominance relationships among male siblings. During the winter we observed dominance interactions of a wild flock of Magpies. A linear dominance matrix with less than 2% reversals was constructed from 547 interactions for 19 HY males. Of these males, 13 were from known nests and none were siblings. The weight ranks of these 13 males at fledging were split and compared. The mean nest rank of the top (rank = 0.94) and bottom (rank = 0.61) birds differed significantly. Hatching order of males may affect relationships even between nonsiblings. Young males apparently know each other individually, and this may indicate flock stability in this aggressive age class. Young male Magpies often take risks near predators in an apparent attempt to advertise their status, and perhaps gain social recognition. It appears that sibling competition is a factor that may determine which birds stay in the natal area and fledging dominance rank has fitness correlates.

Ograniczanie wyników

3 Acta Ornithologica

3 Trost C. H.

1 Gersteli A. T.

1 Reed L. M.

1 Wang X.

1 Webb C. L.

3 1997

Variation in the wing patches of juvenile Black-billed Magpie Pica pica

Advantages of early versus late nesting in Black-billed Magpies Pica pica hudsonia variation in productivity, sex ratio, and fledgling size

The effect of sibling competition on the subsequent social status of juvenile North American Black-billed Magpies Pica pica hudsonia