Argentina Nest-box Video Reveals Unexpected Visitors

Two’s Company, Three’s a Crowd

“What was that!?”

We turn to the computer screen, where Becky Windsor is replaying a video she recorded in one of our swallow nest boxes.

Incubation is a delicate process. Once swallows have set up house and finished laying their eggs (we call it “completing their clutch”), these swallow parents incubate for 15 to 20 days. When the eggs hatch, the parents divide attentions between keeping the nest warm and guarded, and getting enough food to feed hungry, fast-developing nestlings.

Becky is responsible for setting up cameras in select nest boxes to watch the laying and incubation process. These videos will help validate the data we collect with iButtons, which record the temperature in the nest. That will let us verify that a rise in nest temperature means an adult is present in the box. Occasionally, the videos also yield a surprise or two.

One example: Becky’s “What was that!?” was the discovery of three adult swallows huddling together in a nest box:

The sight of two swallows—whom we presume to be the breeding pair for the nest—is not so unusual, particularly here where temperatures at night can dip below freezing. Three swallows, however, is a different story. How exactly the ménage-a-trois came about is unclear, but perhaps the cold weather drove a lone swallow into the box for warmth.

There’s another, more nefarious example. We’ve been looking through footage to satisfy our curiosity about a  mysterious series of events: a nest box has been steadily losing eggs, with no clear cause. Here at last, appears to be a solution:

Fellow Golondrinas intern Dan Albrecht-Mallinger plays back the video once or twice to be sure, but with a few cross-checks he identifies the egg thief as a House Wren, a bird known to steal eggs and suck their yolks, as well as take over nest boxes from other species.

We were not expecting to find predators at our nest boxes. Tierra del Fuego is an island, and in consequence the ecosystem is both distinctive and delicate. The top of the food chain here (removing humans from the picture) is the Patagonian gray fox, a small chubby fellow whom I have had the good fortune to sight at both of our field locations. But foxes don’t get into nest boxes.

Our videos provide a little more insight into the challenges that these swallows face here at “el fin del mundo.” It is a fragile world whose landscape, rich in Austral birch, hearkens back to 200 million years ago when much of the Southern hemisphere was connected in a supercontinent, the single land mass Gondwana.

Both videos are a reminder of how visitors can have an effect on the nest. As anyone who has experienced an unexpected house guest knows, two’s company and three’s a crowd. In the second case, I can only imagine the panic of swallow parents returning to the nest and finding their eggs have disappeared (though, happily, I can report that these birds did in fact re-lay after the House Wren’s visits and they continue to care for their single surviving egg.)