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Orientation can be difficult for nocturnal bird migrants at high northern latitudes because of the large changes of magnetic
declinations, rapid longitudinal time-shifts experienced during a long-distance flight and the invisibility of stars during
the polar summer. Both sunset cues as well as geomagnetic cues have been shown to be of great importance in the orientation
system of Savannah sparrows, Passerculus sandwichensis. We used clock-shift experiments to investigate whether geomagnetic and sunset cues were used for migratory orientation by
wild-caught young Savannah sparrows at high geomagnetic latitudes in Northern Canada. We exposed birds to a 4-h slow clock-shift,
expecting a 60° clock-wise shift in orientation after the treatment. Under natural clear skies in the local geomagnetic field,
the birds responded by showing a significant axial mean orientation directed towards the position of the setting sun in the
NW and towards their preferred migratory direction in the SE. After exposure to the clock-shift for 6 days and nights the
birds showed a clear response to the treatment and shifted significantly towards NNE. Birds that first oriented towards NW
in the experiments before clock-shift tended to shift clock-wise, thus reacted to the clock-shift in the expected way. The
reaction of the individual birds that originally oriented towards SE seems to vary. In summary, our birds did not select a
constant angle (menotaxis) in relation to the sun's position during the experiments, but presumably were affected by the sun
showing phototaxis or followed their magnetic compass. Possible explanations of the unexpected experimental results are discussed.
Electronic Publication 相似文献
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Corey R. Freeman-Gallant 《Behavioral ecology and sociobiology》1997,40(6):395-400
Empirical relationships between parentage and male parental care are commonly interpreted in the context of life-history
models that consider increased offspring survivorship as the only benefit of paternal effort. However, indirect benefits associated
with male care can also influence a male's response to cuckoldry: if females allocate paternity according to their prior experience
with male parental care, it may pay for males to provision extra-pair young in early broods. Here, I assess the relationship
between first-brood parentage and paternal care in a population of Savannah sparrows (Passerculussandwichensis) where a male's fertilization success in the second brood appears to be influenced by his prior parental performance. Based
on the multi-locus DNA fingerprinting of 17 first broods, male feeding effort was influenced by parentage (percent of brood
resulting from within-pair fertilizations) but not by brood size, male mating status (monogamous versus polygynous), timing
of breeding (hatching date), structural size (wing length) or condition (mass). Males provided more care to broods that contained
few within-pair young. This result supports the idea that males provision young to increase their future mating success, but
alternative hypotheses involving male quality and timing of breeding cannot be excluded.
Received: 13 August 1996 / Accepted after revision: 22 February 1997 相似文献
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