On the eve of the World Summit on Sustainable Development, it is timely to assess progress over the 10 years since its predecessor in Rio de Janeiro. Loss and degradation of remaining natural habitats has continued largely unabated. However, evidence has been accumulating that such systems generate marked economic benefits, which the available data suggest exceed those obtained from continued habitat conversion. We estimate that the overall benefit:cost ratio of an effective global program for the conservation of remaining wild nature is at least 100:1.

Abstract. Animal color pattern phenotypes evolve rapidly. What influences their evolution? Because color patterns are used in communication, selection for signal efficacy, relative to the intended receiver's visual system, may explain and predict the direction of evolution. We investigated this in bowerbirds, whose color patterns consist of plumage, bower structure, and ornaments and whose visual displays are presented under predictable visual conditions. We used data on avian vision, environmental conditions, color pattern properties, and an estimate of the bowerbird phylogeny to test hypotheses about evolutionary effects of visual processing. Different components of the color pattern evolve differently. Plumage sexual dimorphism increased and then decreased, while overall (plumage plus bower) visual contrast increased. The use of bowers allows relative crypsis of the bird but increased efficacy of the signal as a whole. Ornaments do not elaborate existing plumage features but instead are innovations (new color schemes) that increase signal efficacy. Isolation between species could be facilitated by plumage but not ornaments, because we observed character displacement only in plumage. Bowerbird color pattern evolution is at least partially predictable from the function of the visual system and from knowledge of different functions of different components of the color patterns. This provides clues to how more constrained visual signaling systems may evolve.

Young brood parasites that tolerate the company of host offspring challenge the existing evolutionary view of family life. In theory, all parasitic nestlings should be ruthlessly self-interested and should kill host offspring soon after hatching. Yet many species allow host young to live, even though they are rivals for host resources. Here we show that the tolerance of host nestlings by the parasitic brown-headed cowbird Molothrus ater is adaptive. Host young procure the cowbird a higher provisioning rate, so it grows more rapidly. The cowbird's unexpected altruism toward host offspring simply promotes its selfish interests in exploiting host parents.

Inter- and intraspecific variations in the sizes of specific avian brain regions correspond to the complexity of the behaviour that they govern. However, no study has demonstrated a relationship between gross brain size and behavioural complexity, a hypothesis that has been proposed to explain the unusually large human brain. I show, using X-rays of museum specimens, that species of bowerbirds that build bowers have relatively larger brains than both related and ecologically similar but unrelated species that do not build bowers. Bower design varies across species from simple cleared courts to ornate, hut-like structures large enough to contain a small child. Furthermore, species building more complex bowers have relatively larger brains, both within each of the two different bower-building clades and across the family as a whole, controlling for phylogeny. Such gross differences in brain size are surprising and may reflect the range of cognitive processes necessary for successful bower building, The relationships are strongest for males, the bower-building sex, although there is a similar trend in females. Because the size and complexity of bower design is targeted by female choice, the observation that relative brain size is related to bower complexity suggests that sexual selection may drive gross brain enlargement.

No abstract

The structure of common cuckoo nestling begging calls differs between the two host-races parasitizing reed warblers (reed warbler-cuckoos) and dunnocks (dunnock-cuckoos; longer syllable duration, lower peak and maximum frequency, narrower bandwidth). Cross-fostering experiments demonstrated that this difference is not genetically fixed but develops through experience. When newly hatched reed warblercuckoos were transferred to dunnock nests, they developed begging calls more like those of dunnockcuckoos, whereas controls transferred to the nests of robins or left to be raised by reed warblers developed calls more typical of reed warbler-cuckoos. We tested the effectiveness of these different calls in stimulating host provisioning by placing in host nests a single blackbird or song thrush nestling (of similar size to a young cuckoo, but lacking its exuberant begging calls); when it begged we broadcast, from a small loudspeaker on the nest rim, recordings of either dunnock-cuckoo or reed warbler-cuckoo begging calls. Playback of dunnock-cuckoo begging calls induced higher levels of provisioning by dunnocks, whereas playback of reed warbler-cuckoo begging calls did so for both reed warblers and robins. We suggest that the young cuckoo (which ejects the host's eggs/chicks and so is raised alone) learns by experience which calls best stimulate host provisioning.

One contribution of 14 to a theme issue 'Challenges in the fight against neglected tropical diseases: a decade from the London Declaration on NTDs'.

Parent birds often give alarm calls when a predator approaches their nest. However, it is not clear whether these alarms function to warn nestlings, nor is it known whether nestling responses are species-specific. The parental alarms of reed warblers, Acrocephalus scirpaceus ("churr"), dunnocks, Prunella modularis ("tseep"), and robins, Erithacus rubecula ("seee") are very different. Playback experiments revealed that nestlings of all three species ceased begging only in response to conspecific alarm calls. These differences between species in response are not simply a product of differences in raising environment, because when newly hatched dunnocks and robins were cross-fostered to nests of the other two species, they did not develop a response to their foster species' alarms. Instead, they still responded specifically to their own species' alarms. However, their response was less strong than that of nestlings raised normally by their own species. We suggest that, as in song development, a neural template enables nestlings to recognize features of their own species' signals from a background of irrelevant sounds, but learning then fine-tunes the response to reduce recognition errors.