There is mounting scientific evidence that global warming is already having profound effects on birds, broader biodiversity, wildlife habitat, and ecosystems. Here are some of the ways that global warming is affecting wildlife:
The ranges of many plants and animals are moving toward the poles and toward higher elevations. For example, the ranges of many British breeding birds were, on average, more than 11 miles farther north in the period from 1988-91 than they were in the period from 1968-72, according to comparisons derived from breeding bird atlases. (British butterflies are also being found farther north.)
Egg-laying, flowering, and spawning are occurring earlier for many species, in some cases disrupting delicate cycles that ensure that insects and other food are available for young animals. For example, Tree Swallows across North America have advanced egg-laying by as many as nine days from 1959 to 1991.
Migration timing and patterns
Spring migration is occurring earlier and fall migration later in many species. For example, 25 migratory bird species are arriving in Manitoba, Canada, earlier than they did 63 years ago; only two are arriving later.
Frequency and intensity of pest outbreaks
Global warming increases droughts in some areas; and spruce budworm outbreaks frequently follow droughts, perhaps because dry weather increases the stress on host trees or allows more spruce budworm eggs to be laid. Spruce budworms can be lethal to spruce trees, and spruce-fir forests are a very important habitat type in the northern hemisphere for a wide variety of plants and animals.