European CuckooCuculus canorusparasitism and host's rejection behaviour in a heavily parasitized Great Reed WarblerAcrocephalus arundinaceuspopulation

Abstract

An unusually high frequency (64%) of European Cuckoo Cuculus canorus parasitism was found in Great Reed Warbler Acrocephalus arundinaceus clutches in central Hungary. Sixty‐four per cent of the parasitized clutches contained one Cuckoo egg, 23% contained two, 10% had three and 3% had four. This means that 58% of the Cuckoo eggs were found in multiply parasitized clutches. In multiple parasitism the laying second Cuckoo removed an egg from the clutch randomly, so preferred neither the host eggs, nor the concurrent Cuckoo egg. Host response towards the parasitic eggs showed 66% acceptance, 12% ejection, 20% desertion and 2% egg burial. We found great variation in both the host and the parasitic egg colour and pattern. This reduces the chance that the parasitic egg's appearance matched that of the hosts’ but, in spite of this, almost perfect mimesis was found in 28% of the Cuckoo eggs. Poorly mimetic Cuckoo eggs were more frequently rejected by Great Reed Warblers than parasite eggs that were very similar to the host eggs. This high level of mimicry sometimes makes it difficult for the observer to identify the parasitic egg, especially when it is similar in size to the host eggs. It is also difficult for the host, as shown by the relatively high recognition error and ejection cost.

Experimental shift in hosts' acceptance threshold of inaccurate-mimic brood parasite eggs

“…(Alvarez 1996) and between years (Brooke et al 1998)). Experimental data are in support of the acceptance threshold model in the great reed warbler that is a host species of the common cuckoo with high rates of multiple parasitism in central Hungary and intermediate levels of responses to naturally laid cuckoo eggs (Moskát & Honza 2002). This host showed higher rejection rates of artificial eggs in response to multiple parasitism than to single parasitism (Honza & Moskát 2005) and it demonstrated plasticity in the responses to the same phenotypic traits involved in egg rejection decisions (this study).…”

“…Egg rejection decisions in this species do not depend on the extent of intraclutch variability of eggs (Lotem et al 1995;Karcza et al 2003), suggesting that other factors, including mimicry of the parasite eggs, may influence the hosts' antiparasite behaviours. At our study site near Apaj (47807 0 N; 19806 0 E), Hungary, the rejection rate is 34% of natural cuckoo eggs (Moskát & Honza 2002) and 71% of artificial non-mimicking eggs . Cuckoo eggs at this site show variable appearance, and typically have a light bluish, almost white, background colour with brown spots, resembling closely the host eggs as judged by human observers (Moskát & Honza 2002).…”

“…At our study site near Apaj (47807 0 N; 19806 0 E), Hungary, the rejection rate is 34% of natural cuckoo eggs (Moskát & Honza 2002) and 71% of artificial non-mimicking eggs . Cuckoo eggs at this site show variable appearance, and typically have a light bluish, almost white, background colour with brown spots, resembling closely the host eggs as judged by human observers (Moskát & Honza 2002).…”

“…We capitalized on consistently high rates of multiple cuckoo eggs laid in host clutches at our study site (Moskát & Honza 2002). Accordingly, when a warbler nest is parasitized once, this demonstrates that the nest can be located and is accessible for the same or other cuckoos on subsequent days.…”

Experimental reduction of ultraviolet wavelengths reflected from parasitic eggs affects rejection behaviour in the blackcapSylvia atricapilla

“…A significant effort has been devoted to studying naturally parasitized host populations to explore a role of parasitic egg mimicry (Moksnes et al, 1993;Edvardsen et al, 2001;Moskát and Honza, 2002). Similarly, many conclusions have been drawn by an experimental approach testing host responses towards both conspecific eggs (Procházka and Honza, 2003;Procházka and Honza, 2004;Lovaszi and Moskát, 2004) and an artificial model egg (Moskát and Fuisz, 1999;Honza et al, 2004).…”