BackgroundThe Palearctic region supports relatively few avian species, yet recent molecular studies have revealed that cryptic lineages likely still persist unrecognized. A broad survey of cytochrome c oxidase I (COI) sequences, or DNA barcodes, can aid on this front by providing molecular diagnostics for species assignment. Barcodes have already been extensively surveyed in the Nearctic, which provides an interesting comparison to this region; faunal interchange between these regions has been very dynamic. We explored COI sequence divergence within and between species of Palearctic birds, including samples from Russia, Kazakhstan, and Mongolia. As of yet, there is no consensus on the best method to analyze barcode data. We used this opportunity to compare and contrast three different methods routinely employed in barcoding studies: clustering-based, distance-based, and character-based methods.ResultsWe produced COI sequences from 1,674 specimens representing 398 Palearctic species. These were merged with published COI sequences from North American congeners, creating a final dataset of 2,523 sequences for 599 species. Ninety-six percent of the species analyzed could be accurately identified using one or a combination of the methods employed. Most species could be rapidly assigned using the cluster-based or distance-based approach alone. For a few select groups of species, the character-based method offered an additional level of resolution. Of the five groups of indistinguishable species, most were pairs, save for a larger group comprising the herring gull complex. Up to 44 species exhibited deep intraspecific divergences, many of which corresponded to previously described phylogeographic patterns and endemism hotspots.ConclusionCOI sequence divergence within eastern Palearctic birds is largely consistent with that observed in birds from other temperate regions. Sequence variation is primarily congruent with taxonomic boundaries; deviations from this trend reveal overlooked biological patterns, and in some cases, overlooked species. More research is needed to further refine the taxonomic status of some Palearctic birds, but large genetic surveys such as this may facilitate this effort. DNA barcodes are a practical means for rapid species assignment, although efficient analytical methods will likely require a two-tiered approach to differentiate closely related pairs of species.

Aim Unique amongst birds, megapodes (family Megapodiidae) have exchanged the strategy of incubating eggs with the warmth of their bodies for incubation behaviours that rely entirely on environmental heat sources. Typically, mound‐builders capture heat released from the decomposition of organic materials, while burrow‐nesters lay their eggs in geothermal or solar‐heated soils. The evolutionary path towards novel incubation behaviours has led to ecological and physiological adaptations unique to megapodes. Here, we present a species tree for all extant megapodes that settles long‐standing debates about megapode evolution: namely, their biogeographical origins and ancestral nesting behaviour. Location Australasia. Methods A time‐calibrated multilocus species tree for all extant megapodes was constructed using *beast. We estimated and compared divergence dates for megapodes obtained from molecular rates, fossils, and a combination of fossils and rates. Using this tree, Bayesian estimation of ancestral nesting behaviour was conducted in BayesTraits and ancestral ranges were estimated in BioGeoBEARS. Results Recent dispersal has led to the recolonization of mainland Australia and New Guinea by Megapodius. Bayesian estimation of ancestral states indicates that mound building is the most probable ancestral nesting behaviour in megapodes (posterior probability = 0.75). Burrow nesting was acquired early in the diversification of the family (at least 14 Ma), followed by a single switch back to mound building. Main conclusions Divergence dates and biogeographical reconstructions strongly suggest that dispersal, and not vicariance, led to the isolation of megapodes in Australasia. We propose that flight‐mediated dispersal to environmentally variable islands is responsible for the behavioural lability in nesting behaviours observed in some Megapodius species today.

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