I’ve been in horse stables where Barn Swallows (Hirundo rustica) were nesting above the horses’ heads, barely out of arms-reach of people coming and going and everyone got on fine. The several pairs of swallows nesting in the barn here, however, are upset whenever I enter the barn, even though they are far overhead on the roof rafters. They seem to feel they should have the barn to themselves and set up a cacophony of distressed chittering when I arrive.
Meanwhile, just down the field the Tree Swallows (Tachycineta bicolor) are carrying nesting materials to their box.
When I was walking past this small pine tree, putting hay out for the horses’ breakfast, I noticed a dark shape near the trunk of the tree. A closer look revealed this female American Robin (Turdus migratorius) sitting on her nest.
Robins are numerous around here. When I was walking along the river, I noticed another mother robin, incubating her eggs.
Robins usually sit tight. That is, even when disturbed by a person close at hand, they stick to their nest and stay still. One season when Birdgirl was working on a nest monitoring study, she came across one robin who wouldn’t budge until she was actually putting her fingers in the nest to check for eggs. Now that’s a dedicated mom. In contrast to robins, Common Grackles (Quiscalus quiscula) are quite easily disturbed. When I walked past a small spruce tree, a grackle made a hasty exit and I knew to look for a nest. Here it is!
The mother retreated to the top of a nearby tree and complained loudly about my presence from the safety of her high perch. With both robins and grackles, the female incubates the eggs, keeping the eggs warm with her body. In order to warm the eggs efficiently, the female develops a brood patch, an area of skin on the belly that loses its feathers toward the end of the egg-laying period. Most birds shed the feathers automatically, though geese and ducks pluck the feathers and add the to the nest. The brood patch also develops extra blood vessels to bring hot blood close to the surface of the skin. When birds return to the nest after a break to resume incubating, they make settling-in movements while they position the brood patch so it is in contact with the eggs. In species where the male also incubates, males may also develop a brood patch. The feathers gradually grow back in after brooding is done.