Egg rejection behaviour in the great reed warbler (<Emphasis Type="Italic">Acrocephalus arundinaceus</Emphasis>): the effect of egg type |
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Authors: | Marcel Honza Csaba Moskát |
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Institution: | (1) Institute of Vertebrate Biology, AS CR, Květná 8, 603 65 Brno, Czech Republic;(2) Animal Ecology Research Group of the Hungarian Academy of Sciences, c/o Hungarian Natural History Museum, Ludovika ter 2, 1083 Budapest, Hungary |
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Abstract: | Egg discrimination in hosts of the common cuckoo Cuculus canorus is frequently studied by experimental parasitism, using model cuckoo eggs. We compared egg rejection behaviour of the great
reed warbler Acrocephalus arundinaceus to either model cuckoo eggs made of plastic or painted real host eggs. We simultaneously parasitised host nests by two different
egg types to simulate cuckoo parasitism. A previous study revealed very similar, ca. 70%, rejection rates against both of
these egg types (beige or bluish background colour maculated with dark brown) when they were used for single parasitism. In
the present study we showed 96% average rejection rates against these egg types when they were applied in multiple experimental
parasitism, causing a more predictable output for rejection behaviour. Hard plastic eggs and painted real eggs were rejected
at similar frequencies, and videotaping revealed that model egg rejection caused extra work for great reed warblers. We revealed
a new type of rejection behaviour, when hosts tried to eject hard-shelled model cuckoo eggs: Hosts made little holes in the
middle part of these plastic eggs by pecking them several times before ejection, as if seeking the possibility to pierce and
hold these eggs in their bills. Painted real eggs were rejected by actually puncturing the eggshell and holding them in the
bill during ejection. No instances of grasp ejection were recorded during filming. Most experimental eggs of either type were
ejected within 1 day after the introduction of the eggs, indicating that hosts made their rejection decisions quickly. Our
observations suggest the lack of plasticity in the mode and timing of ejection behaviour towards experimental cuckoo eggs
of different types in great reed warblers. |
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Keywords: | Brood parasitism Egg ejection Hosts Decision making Cuculus canorus |
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