Rowley review. Bird migration in the southern hemisphere: A review comparing continents

Abstract

To broaden perspectives and stimulate research on migration, I survey the bird species that breed in the northern hemisphere and migrate to the southern hemisphere and species that migrate within the southern hemisphere, comparing routes, seasonal patterns and life histories. Differences in the area and latitudinal extent of land masses on the two sides of the Equator influence patterns of bird migration. In contrast to birds breeding in the northern hemisphere, no land or freshwater birds breeding in the southern hemisphere migrate between continents and only a very few cross the Equator. Furthermore, except for shorebirds, few northern intercontinental migrants reach the southern hemisphere in regions south of the equatorial forest belt, because most encounter, and are filtered out by, suitable habitats en route. Australasia is an extreme case because only 10 land or freshwater migrants from the northern hemisphere regularly occur there (most are uncommon or rare) compared with 42 in Africa and 28 in South America, and no Australasian breeders enter Asia beyond Wallace's Line. Historical geographical and oceanic barriers may be an additional factor limiting migration to Australasia. There are generally no or only slight differences in frequencies of austral migrants within foraging guilds or families across southern continents. Exceptions are rallids, with more migrants in Africa, and cuckoos and nectarivores, with more Old World than New World migrants. Austral migrations are of shorter distances than most of those of the northern hemisphere, and they appear to vary more with respect to routes and patterns. Breeding and non-breeding ranges frequently overlap. Partial migration is common, but there is no evidence that it differs in frequency from that in northern regions. Because climate is generally milder and drier in the southern hemisphere, rainfall is a more important influence on migration than in the north especially in some nomadic birds, but temperature also predicts migration frequency and pathways for many species. These patterns are similar across southern continents, but each continent has its own characteristics. Southern hemisphere migrants seem to display ecophysiologies and orientation mechanisms similar to those found in northern hemisphere species, but very few southern species have been studied. I argue that the variation present among southern hemisphere migrations provides exceptional opportunities to understand the evolution and ecology of migration systems. In order to take advantage of these systems, we need to focus on variation in movement behaviour, on associated syndromes of traits, and on the particular features of natural selection and ecology setting thresholds that lead to the diverse migration patterns observed. © Royal Australasian Orinthologists Union 2008.