New York, June 22 (IANS) Many birds are arriving earlier each spring as temperatures warm along the US East Coast, says a new study that looked at global warming and bird migration. The study, however, found that the farther those birds journey, the less likely they are to keep pace with the rapidly changing climate, according to ScienceDaily.

These are the conclusions of the study by scientists at Boston University who analysed changes in the timing of spring migrations of 32 species of birds along the coast of eastern Massachusetts since 1970.

The researchers, who gathered the data by capturing birds in mist nets, attaching bands to their legs, and then releasing them, found eight out of the 32 species were passing by Cape Cod significantly earlier on their annual trek north than they were 38 years ago.

The reason, the study suggests, is the warming temperatures - which in eastern Massachusetts have risen by 1.5 degrees Celsius since 1970.

Species, such as the swamp sparrow that winter in southern US, are generally keeping pace with warming temperatures and earlier leafing of trees. They migrate earlier when temperatures are warm and later when spring is cool.

Birds that winter further south, like the great crested flycatcher which spends its winters in South America, are slow to change, though. Their migration times are not changing, despite the warming temperatures in New England.

There appears to be good reason for the difference between the short- and long-distance migrants.

Because temperatures are linked along much of the East Coast of the US - an early spring in North Carolina is generally an early spring in Massachusetts - the short-distance migrants can gain insight into when it will be warm further north.

They can follow the flush of leaves and insects all the way to their breeding grounds each year.

Long-distance migrants, though, do not have any good cue for whether it will be an early or late spring on the northern stretches of their migrations.