I believe there were six hungry young swallows lined up on the rail, but it seemed like a lot more given the activity before me. As I watched a pair of adult Tree Swallows feed their charges, I couldn’t help but notice how big their babies were. These fully fledged young were as large – if not slightly larger- than the parents themselves (see below). In this case the term “baby” doesn’t mean “little one.” Only the tawny brown upper plumage and begging behavior served to differentiate the young from the old in this case. (Adult Tree Swallows have iridescent green-blue upper plumage).
Over the course of about a ½ hour, the parent birds never ceased activity. They would glide down low over the marsh waters, stoop to pick insects off the lily pads or in mid-air, then loop back and shove the newly found morsel into one of the awaiting open mouths. The actual transfer was executed in mid-air and the adults never landed.
The acrobatics required to maintain air stability while feeding was made even more dramatic by a very stiff western breeze. The young were lined up with their faces to the wind as if in an air tunnel. An occasional burst would knock one of the young birds off balance and send it kiting vertically into the air – at which point it would gain balance and glide gently back into its proper place on the rail. The adults always approached opposite the wind direction, so the young were required to momentarily break their aerodynamic stance in order to receive their gift. In all case, the food was literally shoved in the open maw with little ceremony.
As each parent neared the chorus line, the young would begin to flutter their wings (see here) and open up their mouths (see above). The bird closest to the arriving parent would strain the hardest and the degree of display intensity diminished further down the line (see beginning photo & here). Somehow, the adults managed to distribute the wealth evenly.
This was not a good day to be a bug. It took barely 30 seconds for a walking/flying insect to go from freedom to foodom as the adults continually looped about and back again. Although I couldn’t tell what kinds of insects were being transferred, they were all fairly large. One even left a nice little string of bug juice from young to parent (see below) as it was being passed. According to the literature, Tree Swallows seem to prefer members of the fly family (Diptera) and they deliberately select for fly food that is over 3 mm in length. When free-styling they will snap at much smaller critters, but when kids are involved they go for the bigger food.
Although only the female incubates the eggs, both parents are involved in feeding. The female holds the upper reproductive hand, however. Scientists call it “extra-pair” mating, but you might call it “fooling around.” The females will often mate with other males, in addition to her chosen partner, and her resulting young will have varied parentage. Tree Swallows have one of the highest rates of philandering in the bird world! The end result of all this messing around appears to produce stronger broods. Fortunately there are no mailmen among Tree Swallows because within any given brood several of the babies would look like him.
Looking down the line of these six hungry chicks, they all looked pretty much alike – especially with their mouths open. So, there’s no telling whose baby belongs to whom. Regardless of what the blood tests say, all of these “little ones” were days away from independence. Tree Swallows are cavity nesters (there is a dentist joke in there somewhere) and the young fledge at about 18-22 days. Once they leave the nest hole, most swallowets seek their independence soon after exiting. There are cases, however, where adults will continue to feed their young for several days after nest departure. This situation was apparently such a case and if I wore a hat, mine would be off for these selfless parent birds. I guess you could call them the ultimate helicopter parents.