What is the formal structure of the mimicry system?

Compared to the ecological variety of brood parasitism, its descriptions in mimicry studies remain rather sketchy and superficial. In general overviews and typologies of mimicry, attention is usually focused on resemblance and deception, species combination and cost-benefit relations of the participants. Brood parasitism belongs to bilateral mimicry systems, meaning that two biological species are involved. Georges Pasteur (1982: 188) describes the cuckoo’s egg mimicry under Kirbyan mimicry (following W. Kirby who noticed this phenomenon in syrphid flies who

Fig. 8.2 An egg of a common cuckoo in the clutch of a common redstart Phoenicurus phoenicurus (Collection of the Natural History Museum of the University of Tartu, photo by the author)

parasite in the nests of bumblebees). Pasteur writes that this kind of mimicry belongs to the aggressive/reproductive type in which the model and the receiver belong to one species and the mimic belongs to another species. In his detailed typology of mimicry, Richard I. Vane-Wright (1976: 42) describes the common cuckoo as belonging to the anthergic aggressive S1+R-type mimicry. In simpler terms, this means that in addition to Pasteur’s criterion of two species where the model (the host’s eggs) and the receiver (the host adult) belong to the same species, Vane- Wright also takes evolutionary influences and interests into account. The mimic’s (cuckoo’s) influence on the receiver is negative and the interests of the mimic and the model do not coincide.

From a biological perspective, in most cases of egg mimicry, two participants (with evolutionary memory) are indeed involved in performing the three roles in the mimicry system. At the same time, the mimicry system can involve an open set of host species as receivers and their eggs as models. There are several host-specific egg patterns in the common cuckoo and specific resemblances are genetically determined and transmitted in the maternal lineage. Researchers have described 11 (Honza et al. 2001: 344), in some estimations 16 (Aviles and M0ller 2004: 57) of such lineages or so-called “gents”. Eggs with specific patterns are, however, not always laid in the nests of the corresponding hosts, so the number of occasional host species may be much larger. This introduces a restrictive condition: if we take the common cuckoo as a species to be the starting point of the description, we should consider egg mimicry as an open system, where the species of neither models nor receivers (nor mimics on the level of gents) are fully determined. If we preferred the strict tripartite model of mimicry, the level of description should follow the relations of one specific lineage to its fixed host species.

When we make a distinction between the biological and the semiotic layers in the egg mimicry of the common cuckoo, several resemblances become observable. The very resemblance between the eggs of the brood parasite and those of the host species (secondary iconic resemblance) seems to be located between two additional resemblances: the primary and tertiary iconic resemblance. The primary ground of a deceptive resemblance between the eggs of cuckoos and hosts is a phylogenetic resemblance of the egg shapes of birds of corresponding size (this also relates to corresponding behavioural adaptations, such as the readiness of a species that does not have any evolutionary experience with brood parasitism to treat objects of various shapes in their nests as their eggs, as shown by studies in classical ethology (Tinbergen 1951: 45)). The tertiary level of iconic resemblances is the relation of camouflage colouration between egg colouration and the surrounding environment to avoid predation. This may influence the colouration of both host and parasite eggs. In addition, there exist resemblances at several other developmental stages, such as correspondences between the behaviour of the cuckoo chicks and the chicks of a particular host species (e.g. Kilner et al. 1999), or similarities in the appearance of the adult cuckoo and hawk species (Payne 1977: 8; Davis and Welbergen 2008). It becomes clear that on the level of semiotic relations, many additional resemblances and connections can be examined.