You won’t find many birds telling you climate change isn’t happening.
In a report by the BTO, new evidence is revealed that shows a range of birds are now laying their eggs earlier in the year as a result of climate change.
39 species are laying between 5 and 30 days earlier than in the mid 1960s. A wide range of types are affected, including raptors, waterbirds, waders, both migrant and resident insectivores and resident seed-eaters. Magpies show the greatest shift, breeding 30 days earlier.
Some previous studies have predicted earlier laying dates to be more constrained in long-distance migrants - yet the BTO data show pied flycatchers and redstarts advancing (by 3 and 4 days respectively) faster than blue and great tits. The average laying date of the migrant species is still approximately a fortnight later than that of the residents.
There are concerns that these shifts could lead to insufficient food being available for chicks as although birds are laying earlier, they aren’t tracking seasonal advances in food availability. So, for example, the timing of leaf emergence and the speed of caterpillar development is changing under increased temperatures but several recent studies suggest that some bird species may be not be responding to the same degree. This would mean chicks not hatching when their food is at peak abundance, as would normally be the case.
The flipside is, however, that earlier laying can also be beneficial as earlier fledging is often related to improved survival to the following year.
Here's a link to the study if you want to read more -
http://www.bto.org/birdtrends2010/