Potential impacts of late-Quaternary environmental changes - from the Last Glacial Maximum to the Little Ice Age - on migratory birds in the Americas

Abstract

The aim of the study was to explore how climatic changes during the last twenty six thousand years may have impacted upon the potential breeding and non-breeding distributions of a range of predominantly migratory bird species that breed in the Americas. The period examined encompasses both the Last Glacial Maximum and the Holocene thermal optimum, the two extremes of climate during the recent geological past. Two contrasting groups of birds were chosen for study: shorebirds in the families Charadriidae, Haematopodidae, Recurvirostridae, Scolopacidae that feed principally on invertebrates and predominantly breed in areas of open vegetation and/or around water bodies; and hummingbirds in the family Trochilidae that are predominantly nectar feeders and occupy a variety of terrestrial habitats, including forests. Climate Response Surface (CRS) models were fitted describing the relationship between each species’ current breeding/non-breeding distribution and a limited set of bioclimatic variables. The models were then used to predict potential past distributions using climate scenarios derived from a series of general circulation model experiments. In all cases a small number of bioclimatic variables with known mechanistic relationships to species’ distributions were selected a priori. Model performance was assessed using AUC, TSS and Kappa values and was generally high. The principal exception was for the non-breeding ranges of many shorebirds that are restricted to coastal areas but which the models projected to be extensive also in inland areas. The results showed that most species’ distributions have potentially shifted, in many cases quite substantially, in response to past climatic changes, but that for most species examined the extent of potentially suitable area had changed relatively little. Greatest impacts were predicted for Arctic-breeding shorebirds, including most members of the Scolopacidae, distributions of which were reduced in extent and shifted during the glacial, extending only as the Laurentide ice sheet decayed during the late-glacial and early Holocene. Climate scenarios for Heinrich events had greater impacts than had that for the glacial maximum, potential distributions of many North American breeding species being shifted to northern South America under these scenarios. The results provide evidence of the vulnerability of many Arctic-breeding species to past climatic changes, whereas species with breeding distributions in tropical regions likely did not change their distributions or range extents to any marked degree.