What is going on? Here in Half Moon Bay, nearly all of the December Barn Swallows this last year were birds or small flocks going north. We have had lots of warm days with offshore winds, which concentrate birds on the move right at the coast. It seems to me that these winter northbound movements of Barn Swallows are becoming more prominent, and are happening earlier and earlier in the season. What I don't understand is if these are truly northbound migrants, or do they return south before the real push north? Their movements look like migration, and they are consistently northbound in this winter period, yet most birds are not in full breeding garb, suggesting they are young or perhaps adults that have not finished molt. When the real push of birds moving to breeding grounds happens, they look the part.
And why only Barn Swallows, and not other swallows. I have been intrigued by these swallow movements for years, and this past year there were more than ever.