Bird migration is a highly dynamic natural system heavily influenced by the weather, at the local, regional, and continental scale. Birds do not migrate when it’s raining. They also tend to avoid headwind conditions. In short, weather conditions that are unfavorable for flying long distances.
This is why bird migration often seems a boom-and-bust phenomena: all of a sudden, there are lots of migrants, and, as quickly, the woods could be empty! That was the case here at Cabot Head last week. After a few days of bad weather, conditions improved and, on Monday, April 22nd, there was a big push of many migrants, resulting in a season-record of 116 birds banded. Kinglets of both species were again the kings of the day, but there were also many Brown Creepers, Song Sparrows, and Hermit Thrushes. We also banded one Brown Thrasher! Diversity was not extremely high but numbers certainly were.
Birds were most likely taking advantage of a window of good weather: the following day, a strong South wind was blowing, preventing net opening, and also, pushing rain-laden clouds. Soon, intense rain was falling once again in this wet Spring, closing down any chance of migration. Before the skies opened, though, there was a good passage of Blackbirds (Common Grackles, Red-winged Blackbirds, and a few Brown-headed Cowbirds), American Robins, and Northern Flickers, as well as Sharp-shinned Hawks.
Thankfully, drier weather returned in mid-week and normal migration resumed. Numbers and diversity of birds were still relatively low, possibly hampered by the cold. Very few warblers, for example, have been seen: even hardy and early species like Pine and Yellow-rumped Warblers have been, so far, detected only in small numbers. But, on April 24th, the FOY Palm Warbler was seen.
In the last moment of night, on April 25th, the resounding voice of the Eastern Whip-poor-will was heard across Wingfield Basin. I had trouble believing my ears, as it is an extremely early date to have this moth-eater return to Cabot Head: the earliest previous date was May 3, 2018.
The following day, rain was falling again. During a break in the afternoon, a Northern Mockingbird was seen briefly. It is also a very early date for this occasional visitor to Cabot Head. May 10th, in 2005 and 2014, was the previous earliest date. What is better than rain? Snow, of course! Cabot Head was white again for a short time in the morning of the 27th, shivering under a strong and cold North wind.
Despite the return of a more clement weather, there was not many birds around, either in the nets or in the sky. It is even possible that some birds retreated South in a reverse migration, to find food and better weather, in a process not quite well understood.
As of this writing, on April 29th, no long-distance migrants have been detected. Black-throated Green warblers could arrive any time soon now, and indeed, have been detected in April in 11 years out of the previous 17 years of monitoring, with April 23rd, 2014 the earliest date.
There is always tomorrow!