As yesterday’s post indicated, the progression in which signs of spring appear remains much the same, but the timing of this progression is changing. Ornithologists have determined that modern climate change has resulted in an advancement of spring phenology throughout the Northern Hemisphere.
Many birds are arriving on their breeding grounds earlier in response to these changing conditions. Past research has focused on correlating climatic changes on breeding grounds with early arrival. However, it appears that climate variability on the wintering grounds of temperate species also plays a part in these short-distance migrants’ arrival on their breeding grounds.
Many climatic factors are involved in this phenomenon. The annual variation in temperature on the wintering grounds of American robins was found to be strongly related to their first-arrival date. Red-winged blackbirds’ first arrival dates were most influenced by precipitation during winter and spring months.
These and other changes in migratory patterns can have life or death consequences — birds arriving early on their breeding grounds face the possibility of adverse conditions and limited resources.
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