Moulay Lahcen El Kabiri, deputy head of the United Nation's Bonn-based Convention on Migratory Species, said that warmer climates are confusing migratory species including bats, dolphins, antelopes and turtles, causing them to end up at the wrong place at the wrong time.

"They are the most visible warning signs -- indicators signaling the dramatic changes to our ecosystems caused in part by climate change," he explained to delegates on Monday, the opening day of a May 7-18 UN meeting to discuss how to offset global warming.

Not only are birds and animals mistiming their migrations, El Kabiri said, some of them do not even make the attempt as seasonal changes become less clear. Yet unpredictable or extreme weather, such as heatwaves, droughts or cold snaps, could make them vulnerable.

Cranes, for example, are remaining in Germany during the winter rather than flying south to Spain. But, El Kabiri warned, "a harsh winter (in Germany) could decimate the population."

A multitude of problems

Rising sea levels could also flood habitats for many shore birds, he said.

Birds are also reported to be hatching earlier in warmer climates, but are still not keeping up with the insects they feed on and which are flourishing even earlier. El Kabiri said Pied Flycatcher birds in Europe are not finding enough caterpillars with which to feed their chicks.

Not just birds, but other migratory species are also being affected by climate change, El Kabiri, a Moroccan, told the Reuters news agency.

Some whales, for instance, are not finding the fish and plankton they normally feed on, which is now thriving in warmer waters closer to the poles.

The Convention on Migratory Species and the UN's African Eurasian Migratory Waterbirds Agreement said a series of events on May 12 and 13 will be used to highlight how climate change is affecting birds.