Northern RW Swallows in Concord, CoCo County
On December 23rd, 2020, early evening at Ellis Lake Park in Concord, Contra Costa County, I found one Northern Rough-winged Swallow, the next day at the same time of day, there were already two swallows. Thereafter, every day for the next two weeks, one or two swallows were seen in this park and once also in another park in Concord, at Hillcrest Park (about 5 km, north of Ellis Lake Park). After several of my visits to Ellis Lake Park I noticed that these birds returned daily to the park according to the same pattern, usually for a short time, about 35-45 minutes in evening where they foraged over the lake / lakes until sunset (the birds were never seen in this park before evening). What I also noticed is that these swallows or a swallow (in two cases) always left the park around sunset and headed towards the north.
There are several scenarios I am considering regarding these swallows.
At first I thought I had witnessed extremely late southbound migrants, then, I considered also, the possibility of wintering birds in this area, I knew from my collected data from this park that these birds would not roost overnight in Ellis Lakes Park, but did so likely somewhere north of the park. In this scenario, the daily visits to the park likely involved, of course, the same two birds. However, during a recent visit to E.L.P. I began to consider the possibility that I may have perhaps witnessed rather the extremely early ongoing northbound migration of this species, in this scenario each of my daily observations concerned of other individuals of this species. The birds leaving the park after sunset simply continued their northbound journey rather than going to the roost somewhere north of the park.
Albert W. Linkowski