Brain size and morphology of the brood-parasitic and cerophagous honeyguides (Aves: Piciformes).

Honeyguides (Indicatoridae, Piciformes) are unique among birds in several respects. All subsist primarily on wax, are obligatory brood parasites and one species engages in 'guiding' behavior in which it leads human honey hunters to bees' nests. This unique life history has likely shaped the evolution of their brain size and morphology. Here, we test that hypothesis using comparative data on relative brain and brain region size of honeyguides and their relatives: woodpeckers, barbets and toucans. Honeyguides have significantly smaller relative brain volumes than all other piciform taxa. Volumetric measurements of the brain indicate that honeyguides have a significantly larger cerebellum and hippocampal formation (HF) than woodpeckers, the sister clade of the honeyguides, although the HF enlargement was not significant across all of our analyses. Cluster analyses also revealed that the overall composition of the brain and telencephalon differs greatly between honeyguides and woodpeckers. The relatively smaller brains of the honeyguides may be a consequence of brood parasitism and cerophagy ('wax eating'), both of which place energetic constraints on brain development and maintenance. The inconclusive results of our analyses of relative HF volume highlight some of the problems associated with comparative studies of the HF that require further study.

Innovative foraging behaviour in birds: what characterizes an innovator?

Innovative foraging behaviour has been observed in many species, but little is known about how novel behaviour emerges or why individuals differ in their propensity to innovate. Here, we investigate these questions by presenting 36 wild-caught adult male Carib grackles (Quiscalus lugubris) with a novel problem-solving task. Twenty birds solved the task ("innovators") while 16 did not ("non-innovators"). We compared innovators to non-innovators and explored variation in latency to innovate to determine the characteristics of an innovative bird. Innovativeness was not predicted by any morphological trait, but innovators had higher exploration scores and lower object neophobia scores than non-innovators. Within the innovators, latency to innovate was positively correlated with learning speed. Video analysis also revealed a marked difference in the way individuals interacted with the novel apparatus: when innovators contacted the correct part of the apparatus, they continued to do so until they solved the problem. Non-innovators often contacted the correct part of the apparatus, but did not persist in doing so. The importance of obstacle movement cues was confirmed by an experiment where they were manipulated.