Adaptations by great reed warblers to brood parasitism: A comparison of populations in sympatry and allopatry with the common cuckoo

Publication Type:Miscellaneous
Year of Publication:2002
Authors:Moskát, C., Szentpeteri, J., Barta, Z.
Keywords:Acrocephalus arundinaceus, adaptation, Brood parasitism, Cuculus canorus, Egg rejection, Interclutch variation, Intraclutch variation
Abstract:

Egg rejection behaviour, as an antiparasite defence against brood parasitism was compared in two great reed warbler Acrocephalus arundinaceus populations. In central Hungary the host population lives in sympatry with the common cuckoo Cuculus canorus, and it is heavily parasitised (ca 66%). In central Greece the great reed warbler occurs in allopatry with the cuckoo, so it is not parasitised at all. Experimental parasitism with poorly mimetic (often called 'non-mimetic') artificial cuckoo eggs revealed a 100% rejection rate towards the foreign eggs in the Greek population, but the Hungarian hosts accepted 29.4% and rejected 70.6% of the model cuckoo eggs. No other rejection type than ejection was observed. The significantly higher level of rejection in Greece than in Hungary suggests that the Greek great reed warbler population is an abandoned host population of the cuckoo, which kept its egg recognition ability. A computer-based image analysis of host's clutches revealed that interclutch variation in egg colour was greater than intraclutch variation in the Hungarian population, but not in the Greek population. Spottedness of eggs were similar in both populations. Generally, a tendency for a higher interclutch variation was found in Hungary. Intraclutch variation was more similar in the two populations, but for the colour variables it showed a lower value in Hungary than in Greece. The heavy cuckoo parasitism in Hungary is suggested to be the main cause for the increased interclutch variation in relation to intraclutch variation in egg appearance among great reed warbler clutches. The high interclutch variation reduces the chance that the parasite egg's appearance matches that of the hosts', which facilitates hosts' egg discrimination.

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