GLOBAL WARMING AND EGG SIZE OF BIRDS

Global warming or climate change is known to have many effects on plan ts, hut there has been relatively little research on global warming an d animals, partly because too few long-term studies have been carried out. In northern areas, mean temperature is believed to be rising, and indeed during the last decades mean spring temperatures in Finnish La pland have increased. In 1975-1993, mean air temperature during the ma in egg-laying period of a pied flycatcher Ficedula hypoleuca populatio n correlated positively and significantly with mean egg volume of that population. Since larger eggs enjoy improved hatching success, global warming may alter birds' reproductive strategies, because warmer weat her may allow females to invest more resources in reproduction. This i n turn may help birds rapidly conquer new areas when they become avail able and compensate for rising mortality rates to be expected elsewher e where warming means desiccation.