Global Warming For the Birds

Global Warming for the Birds

by Deb Powers

A lot of folks out there seem to think that global warming is for the birds, but a group of researchers in California have taken a serious look at how global warming is actually affecting their local birds. Morgan Tingley, a doctoral student at University of California at Berkeley, headed up a study that traced the migration patterns of local birds over the past century. Their discovery? Birds will move if the climate becomes unfavorable to them.

Tingley and his co-researchers used data data from a survey of 82 sites in the Sierra Nevada and details the changes in birds' geographic range over the course of a century. Over the course of a century, the data shows, average temperatures have risen 1.4 F. and average rainfall during the breeding season has increased about a quarter inch since the early 1900s.

As a result of this, Tingley says, 48 of the 53 bird species that they studied have moved their preferred habitats to areas that fit their preferences better. The species that chose to stick it out and adapt, according to the study's authors, are those that are better able to "adapt to human-altered habitats". They include the Anna hummingbird and the scrub jay, two birds that are quite happy to enjoy the largesse scattered by their human friends in bird feeders.

For many of the birds, the change in weather meant that they moved their breeding grounds further north, where cooler temperatures prevail. Others that prefer warmer temperatures have extended their home bases to the south. The study is scheduled to be released in an early edition of the journal Proceedings of the National Academy of Sciences, and was conducted in coordination with Audobon California.

The researchers used records from the early 1900s that detailed the species of birds found in areas of the Sierra Nevada. The modern researchers hiked the same trails and recorded the species that they found, and where they were found. They did a similar study last year that found many small mammals had moved to higher elevations. The new study focusing on birds shows that they are following similar patterns.

One very interesting note from the study references predictive computer models that were used to suggest the movements of bird migration. While many climate skeptics attempt to debunk the models used for predicting the possible effects of global warming, the researchers in this study found that the models they used were extremely accurate.

An unrelated study from the U.S. Geological Survey found that many Alaskan birds are choosing to stay in Alaska throughout the winter rather than migrate south to Mexico.

"This increase in wintering numbers of brant in Alaska coincides with a general warming of temperatures in the North Pacific and Bering Sea," said David Ward, the lead author of the study and a USGS researcher at the Alaska Science Center. "This suggests that environmental conditions have changed for one of the northernmost-wintering populations of geese."

 The particular bird studied, the Pacific brant, breeds primarily in Alaska and moves south to winter along the Pacific coast as far south as Mexico. It used to be that about 90% of the Alaskan population of brant moved south each winter, but recent head counts have found that less than 70% are heading south for the winter these days.

The USGS had found in earlier studies that there were significant changes in the migration patterns of a number of fish species along the Alaskan coast, and feel that the changes in brant migration are linked to the same climate changes. They also pointed to the decreasing ice along the coast as a factor in keeping the Pacific brant at home. With less of the sea coast iced over, they say, there is easy access to larger quantities of eel grass, a high nutrient grass that is a major part of the preferred diet for the brant.

These studies highlight how small changes in the environment can result in larger changes in the overall world. Scientists studying the Pacific brant, for instance, fear that the population of the bird could be seriously affected if an unexpected freeze kills off the supply of food for those staying behind.

Likewise, Audobon researchers are concerned that the disappearance of certain bird species from some areas of the Sierra Nevada could have larger consequences. Some of the bird species, for instance, are vital in helping to spread seeds of certain plants. Without those birds, the plant species could die out. Each of those changes can bring more changes, until the world is one that we would hardly recognize.

Image credit: haiinee@stock.xchang