Egg rejection behaviour in the great reed warbler (Acrocephalus arundinaceus): the effect of egg type

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.

Why do brood parasitic birds lay strong-shelled eggs?

“…As revealed by experiments with model eggs, some hosts of the Common Cuckoo, e.g., the Great Reed Warbler which is relatively large in terms of body mass and bill-size and is readily able to use grasp ejection of cuckoo eggs, always first try to puncture eggs (Lotem et al, 1995;Antonov et al, 2006a; for similar results see also Honza and Moskat, 2008). Comparisons with the evidence from several similar studies on other Sylviidae suggest that puncture ejection is the ancestral mode of rejection in this family Procházka and Honza, 2003;Honza et al, 2004).…”

Nest sanitation in passerine birds: implications for egg rejection in hosts of brood parasites

“…Larger objects were mostly buried only in pre-incubation, whereas smaller objects were mostly ejected during pre-incubation and incubation (Guigueno and Sealy 2009). In a related study, Honza and Moskát (2008) found that the type of material (plastic or painted host eggs) influenced whether hosts punctured the object (painted host egg) or pecked the object over and over to create a hole in the hard material (plastic egg); however, both object types were rejected at similar frequencies.…”

Discordancy or template-based recognition? Dissecting the cognitive basis of the rejection of foreign eggs in hosts of avian brood parasites

“…For treatments, we manipulated one or more of the hosts' own eggs in a nest, painting dark brown spots (see below) onto the eggshell. We used painted C. Moskát and others real eggs, following Honza and Moskát (Honza and Moskát, 2008). The eggs of great reed warblers are suitable for such types of painting experiments because a great reed warbler egg is as large as a cuckoo egg (Török et al, 2004).…”

“…This period of monitoring was justified by our previous studies on this host species, where latency of rejection was 1-5days for each type of parasitic egg: for real cuckoo eggs in natural parasitism (Moskát and Hauber, 2007), and plastic model cuckoo eggs and painted great reed warbler eggs in experimental parasitism (e.g. Honza and Moskát, 2008).…”