The application of molecular genetic techniques has revolutionized our view of avian mating systems. Contrary to prior expectations, birds are only very rarely sexually monogamous, with 'extra-pair offspring' found in approximately 90% of species. Even among socially monogamous species, over 11% of offspring are, on average, the result of extra-pair paternity (EPP). Based on over 150 molecular genetic studies of EPP in birds, we review two topical areas: (i) ecological explanations for interspecific variation in the rate of EPP; and (ii) evidence bearing on the adaptive function of EPP. We highlight the remaining challenges of understanding the relative roles of genes and ecology in determining variation between taxa in the rate of extra paternity, and testing for differences between extra-pair offspring and those sired within-pair.

Biodiversity hotspots have a prominent role in conservation biology, but it remains controversial to what extent different types of hotspot are congruent. Previous studies were unable to provide a general answer because they used a single biodiversity index, were geographically restricted, compared areas of unequal size or did not quantitatively compare hotspot types. Here we use a new global database on the breeding distribution of all known extant bird species to test for congruence across three types of hotspot. We demonstrate that hotspots of species richness, threat and endemism do not show the same geographical distribution. Only 2.5% of hotspot areas are common to all three aspects of diversity, with over 80% of hotspots being idiosyncratic. More generally, there is a surprisingly low overall congruence of biodiversity indices, with any one index explaining less than 24% of variation in the other indices. These results suggest that, even within a single taxonomic class, different mechanisms are responsible for the origin and maintenance of different aspects of diversity. Consequently, the different types of hotspots also vary greatly in their utility as conservation tools.

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Understanding the ecological mechanisms that underlie extinction is fundamental to conservation. It is well established that not all taxa are equally vulnerable to extinction, but the reasons for these differences are poorly understood. This may be, in part, because different taxa are threatened by different mechanisms. Theoretically, sources of extinction risk that perturb the balance between fecundity and longevity, such as human persecution and introduced predators, should be particularly hazardous for taxa that have slow rates of population growth. In contrast, sources of extinction risk that reduce niche availability, such as habitat loss, should represent a particular threat to taxa that are ecologically specialized. Here we test these predictions by using a phylogenetic comparative method and a database on 95 families of birds. As theory predicts, extinction risk incurred through persecution and introduced predators is associated with large body size and long generation time but is not associated with degree of specialization, whereas extinction risk incurred through habitat loss is associated with habitat specialization and small body size but not with generation time. These results demonstrate the importance of considering separately the multiple mechanisms that underlie contemporary patterns of extinction. They also reveal why it has previously proven so difficult to identify simple ecological correlates of overall extinction risk.life history ͉ body size

Global conservation strategies commonly assume that different taxonomic groups show congruent geographical patterns of diversity, and that the distribution of extinction-prone species in one group can therefore act as a surrogate for vulnerable species in other groups when conservation decisions are being made. The validity of these assumptions remains unclear, however, because previous tests have been limited in both geographical and taxonomic extent. Here we use a database on the global distribution of 19,349 living bird, mammal and amphibian species to show that, although the distribution of overall species richness is very similar among these groups, congruence in the distribution of rare and threatened species is markedly lower. Congruence is especially low among the very rarest species. Cross-taxon congruence is also highly scale dependent, being particularly low at the finer spatial resolutions relevant to real protected areas. 'Hotspots' of rarity and threat are therefore largely non-overlapping across groups, as are areas chosen to maximize species complementarity. Overall, our results indicate that 'silver-bullet' conservation strategies alone will not deliver efficient conservation solutions. Instead, priority areas for biodiversity conservation must be based on high-resolution data from multiple taxa.