Changes in autumn arrival of long-distance migratory birds in Southeast Asia

Climate-change-induced phenological changes in migratory birds are predicted from ecological theory and have been well-documented in temperate-zone breeding areas. By contrast, changes in arrival date on tropical wintering grounds have not been reported. To address this gap, we analysed birdwatchers’ records of first arrival dates of 9 species of long-distance migratory birds in Singapore from 1987 to 2009. The study species included 1 raptor, 3 waders and 5 passerines. We compared the relative influence of year, Southern Oscillation Index and observer effort on arrival date. There was strong evidence for an arrival delay of approximately 2 d yr^-1 (95% confidence intervals of 1-3 d) in Japanese sparrowhawk Accipiter gularis and curlew sandpiper Calidris ferruginea, but there was no change in arrival date for the other 7 species. We hypothesise that climate change is causing a shift in migration timing for some birds in Southeast Asia. A mechanism for the delay in these long-distance migrants may be that warmer temperatures enable species to remain on northern breeding grounds longer. Delayed arrival on the wintering grounds may have cascading effects on a migratory species’ annual cycle, for example by influencing the arrival date at the breeding grounds, which can impact fitness. These potential impacts underscore the need for further work on the effects of climate change on migratory species in the tropics.