Predation risk affects trade-off between nest guarding and foraging in Seychelles warblers |
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Authors: | Komdeur Jan; Kats Romke K H |
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Institution: | Zoological Laboratory, University of Groningen, PO Box 14, 9750
AA Haren, The Netherlands, and Department of Zoology, University of Melbourne,
Parkville, Victoria 3052, Australia |
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Abstract: | The fitness costs of egg loss for Seychelles warblers (Acrocephalus
sechellensis)on Cousin Island are considerable because warblers have a
single-eggclutch and no time to lay a successful replacement clutch. Onthe
islands of Cousin and Cousine, with equal densities of Seychellesfodies
(Foudia sechellarum), nearly 75% of artificial eggs placedin
artificial nests were predated by fodies after 3 days. OnAride Island with no
fodies present, loss of artificial eggswas not observed. Female warblers
incubate the clutch, and malewarblers guard the clutch when females are
absent. Deterrenceof fodies by male warblers is efficient: loss rate of eggs
fromunattended warbler nests was seven times as high as from attendednests,
and the more nest guarding, the lower the egg loss andthe higher the hatching
success. Egg loss is independent ofthe amount of incubation by females. There
is no trade-off betweenincubating and foraging by females. Nest guarding
competes withforaging by males, and this trade-off has a more pronounced
effecton egg loss when food availability is low. The transfer of breeding
pairsfrom Cousin to either Cousine with egg-predating fodies or toAride
without fodies allowed us to experimentally investigatethe presumed trade-off
between nest guarding and foraging. OnCousine, individual males spent the
same amount of time nestguarding and foraging as on Cousin, and egg loss was
similarand inversely related to time spent nest guarding as on Cousin.Males
that guarded their clutch on Cousin did not guard theclutch on Aride but
allocated significantly more time to foragingand gained better body
condition. Loss of warbler eggs on Aridewas not observed. Time allocation to
incubating and foragingby individual females before and after both
translocations remainedthe same. |
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Keywords: | egg defense egg predation foraging parental care reproductive success Seychelles warbler trade-offs |
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