Cuckoo females preferentially use specific habitats when searching for host nests

Egg mimicry is an important adaptation of common cuckoos, Cuculus canorus, against rejection of eggs by their respective hosts. A precondition for the maintenance of egg mimicry is that female cuckoos find hosts with a matching egg type. Experimental evidence indicated that habitat imprinting may be important for host selection. We tested whether the spacing and laying patterns of female cuckoos in the field are compatible with the supposed habitat-imprinting mechanism. We observed 16 females, with the help of radiotelemetry; of seven females, we observed directly 26 egg layings and 27 nest visits without laying. As expected if females were imprinted on different vegetation types, (1) the distribution of vegetation types differed between female home ranges, (2) female habitat use differed from average habitat availability within the egg-laying area (habitat preference), (3) females visited nests and deposited their eggs in the habitat they preferred, and (4) females laid their eggs consistently in a particular habitat type, irrespective of the host species. These results indicate that cuckoo females show habitat preference when searching for suitable host nests. Hence our data are compatible with the habitat-imprinting hypothesis, but owing to the habitat specificity of hosts the data cannot disprove a potential role of host specificity in cuckoo females.