Forecast and Analysis

Migration alert: Early-to-mid March warmth and bird migration in the East, not so much in the West

Andrew Farnsworth The Cornell Lab Mar 03, 2021

We all know the proverb that speaks to the changes that occur in our atmosphere during March. The season’s variability in weather, and climate, is an expectation. And birds respond to these changes, as the early season migrants move away from areas where they have spent their winter and move toward breeding areas; this is particularly true when conditions are favorable. And a primary factor in these movements is warming temperatures.

March 2012 was extreme this regard, with anomalous warmth in many areas of the US, especially the eastern half of the country. And with this warmth came early and intense movements of birds – see this publication by La Sorte et al. 2016 detailing the extremes of the month’s movements, this BirdCast post from 25-26 February 2012 for an ornithological harbinger of what would come, and this and this for a climatological perspective on what transpired).

While not predicted to be similarly anomalous in terms of the departures from normal temperatures, a broad warming trend is forecast for the 8-16 March 2021 window. Below are one-week and two-week outlooks for temperatures for the United States. Note the distribution of the darker red colors, representing high probabilities of warmer than normal temperatures. Although these are not indicative of the temperature, they are broadly indicative of the warmth and its extent. And where temperatures are above normal, so, too, will early season migration be more intense than normal.

The contrasting pattern of cooler than normal temperatures and less intense migration is also true – cooler than normal temperatures in the western US, associated with a strong bow to the south in the jet stream, will beget lower than normal migration intensities, particularly where precipitation is forecast, especially west of the Sierras.

Stay tuned to the predictions, ours included (!), and please go birding and report what you see!