Abstract: Common cuckoos (Cuculus canorus) are obligate brood parasites, laying eggs into nests of small songbirds. The cuckoo hatchling evicts all eggs and young from a nest, eliminating hosts' breeding success. Despite the consistently high costs of parasitism by common cuckoos, great reed warbler (Acrocephalus arundinaceus) hosts sometime accept and other times reject parasitic eggs. To explore the cognitive basis of this seemingly maladaptive variation in host responses, we documented differences in egg rejection rates within 1-day periods just before and during the egg-laying cycle across host nests. Hosts rejected cuckoo eggs at 28% of nests during the pre-egg-laying stage, but when cuckoos exchanged the first host egg with the parasite egg, rejections increased to 75%. Even later, when several host eggs remained in a nest after parasitism, rejection rate fell to 37.5%. Experimental parasitism with conspecific eggs on the first and second day of host laying showed a similar directional change in relative rejection rates, dropping from 35 to 0%. Mistakes in egg discrimination (ejection error and ejection cost) were observed mostly in the latter part of the laying cycle, mainly when nests contained 5-6 eggs. These correlational and experimental patterns of egg rejection support a cognitive process of egg discrimination through several shifts in hosts' optimal acceptance thresholds of foreign eggs. The results are also consistent with the evolution of foreign egg rejection in the context of nest-sanitation (i.e. the removal of foreign objects). Our results suggest that common cuckoo hosts may recognize more eggs than they reject. This implies that the experience of the host with one or more of its own eggs in the clutch is a key factor in rejecting parasite eggs by allowing inspection and learning about their own clutch.

Abstract: Summary Spatial orientation has played an extremely important role in the development of ideas about the behavioral capacities of animals. Indeed, as the modern scientific study of animal behavior emerged from its roots in zoology and experimental psychology, studies of spatial orientation figured in the work of many of the pioneering researchers, including Tinbergen (), von ), Watson () and .

Abstract: Summary In this chapter I want to stand back from the splendid empirical work on animal cognitive capacities that is the focus of this book, and look at the broader context of cognitive concerns within which the work can be viewed. Indeed even the term `cognitive ethology' currently connotes and denotes more than is represented here, as other collections of articles, such as and , exemplify. I include the current descendants of behavioristic learning theory, evolutionary epistemology, evolutionary psychology and the recent comparative turn that has been taken in cognitive science. These several approaches, despite their considerable overlap, often appear independent and even ignorant of one another. Like the proverbial blind men feeling the hide of an elephant, they touch hands from time to time, yet collectively have only a piecemeal and distributed understanding of the shape of the whole. Although each approach may indeed need the space to work out its own conceptual and methodological preoccupations without confounding interference from other views, a utopian spirit envisages an ultimate coming together, a more comprehensive realization of the synthetic approach to animal cognition that is this book's theme.