Birds are changing their winter ranges as a result of climate change. Average temperatures in January have increased more than five degrees Fahrenheit in the continental United States between 1966 and 2005, and the ranges of many species of birds in the early winter have shifted northward.

Scientists at the National Audubon Society analyzed the results of Christmas Bird Count data between 1966 and 2005. Of the 305 species that were widespread enough to be studied, 177 species (58 per cent) had their ranges move northward. More than 60 of these species had their ranges move northward by more than 100 miles in those 40 years. Seventy-nine species (26 per cent) had their ranges move southward, and the trends were not statistically significant for the remaining 49 species (16 per cent). These results are consistent with the global warming hypothesis; the majority of species shifted northward and the shifts were greater in areas with the greatest warming.

Land birds showed the greatest shift; 64 per cent of these species moved northward, with an average shift of almost 50 miles. Almost half (46 per cent) of the coastal species moved northward, with an average northward shift of about 20 miles. And almost half (52 per cent) of the waterbirds moved northward, with an average change of about 15 miles northward.

Range shifts away from the coast were found for twice as many species as had their ranges shift toward the coast. This is consistent with global warming since higher temperatures inland might translate into greater food availability due to less frozen ground and more open water.

Other explanations may contribute to these shifts but they do not explain these changes as well as does global warming. These results are not consistent with known increases or decreases in bird populations. And bird feeding does not explain the northward shifts in the many woodland and water bird species that do not utilize this supplemental food source. Habitat changes do not explain these changes either.

Here are some of the highlights relative to species commonly found on our local Christmas Bird Count. The following list shows how many miles each species range has shifted; a positive number indicates a northward shift and a negative number indicates a southward shift.

brant 193 miles

Canada goose 120

mute swan -123

gadwall 149

American black duck 182

greater scaup -136

surf scoter -47

white-winged scoter 130

black scoter -233

bufflehead -267

hooded merganser -93

red-breasted merganser 317

red-throated loon -277

common loon -95

northern gannet 83

double-crested cormorant 117

great cormorant -25

turkey vulture 53

northern harrier 77

American kestrel 54

black-bellied plover 114

killdeer -78

sanderling -169

herring gull 24

great black-backed gull -24

mourning dove 147

belted kingfisher 98

red-bellied woodpecker 60

northern flicker 192

blue jay 89

American crow 89

black-capped chickadee 90

red-breasted nuthatch 244

Carolina wren 57

eastern bluebird 114

European starling 86

cedar waxwing 189

rufous-sided towhee 215

song sparrow 74

white-throated sparrow 109

dark-eyed junco 116

purple finch 433

house finch 270

American goldfinch 219

house sparrow 77

So what can we conclude? Certainly bird distributions are changing. Northward changes are twice as common as are southward changes, which may be due to the observed five degrees Fahrenheit increase in the average temperatures in January. These are the impacts of climate change in the past 40 years, so how much will they change in the future? What other changes are occurring?

Whether these observed temperature changes are due to people and the increased levels of carbon in our atmosphere is another topic that will not be debated here. But this study can serve as a canary in the coal mine that documents and warns us of ongoing environmental changes.