This is the renovated building of the USFWS field office. The entire place used to be a CIA listening unit, built by the U.S. military in the 1970s to monitor the goings-on of Puerto Rican independistas.
I took a completely random Spanish elective on Puerto Rican literature during my junior year of college, never dreaming that it would be of any use. Funny how these things work out.
This is a nest of a yellow-shouldered blackbird (called “la mariquita,” or ladybug, here). Yellow-shoulders are both endemic to Puerto Rico and endangered, hence the many permit hoops I had to jump through. The main forces contributing to their decline are loss of habitat and severe brood parasitism by the shiny cowbird, a bird that arrived on the island in the 1940s. Cowbirds lay their eggs in other birds’ nests, preferring one or two species as their primary hosts. Almost all of the yellow-shoulder’s nests are parasitized to some degree. I found this nest with only two blackbird eggs (top two on left) and four cowbird eggs.
The yellow-shoulder was listed as endangered in 1976. Since then, the FWS and PR Department of Natural Resources have implemented aggressive monitoring programs to control parasitism and promote chick and fledgling survival. Over the past 30 years, the population has increased from only ~200 breeding individuals to more than 800. It’s been inspiring to meet the people who have been so invested in the protection of these guys.
Beginning in the 1980s, people involved in the recovery project began controlling the cowbird population and building artificial nests for the yellow-shoulders to use. In the foreground is an early prototype, while in the background you can see the newer nests made of PVC.
Up until now, their tarsal vein is still visible, enabling me to take blood from their leg. But you can see the tarsus darkening as the skin hardens, making it progressively trickier to stick them in the right spot.
I should explain that my reaction comes after three years of looking at redwing chicks, which develop brown female-like plumage first (see above). But yellow-shoulder males, females and nestlings all look the same, which really did take some getting used to.
The breeding season this year is wildly asynchronous. The PR folks told me they’d never seen nests with fledglings alongside nests still on eggs. If I do find evidence of cheating, theory suggests this weird temporal fluke might help explain its occurrence. (Based on behavioral and morphological evidence, I’m expecting to find less cheating in the yellow-shoulders than in the redwings.)
One drawback of the artificial nests is that mite infestations can get pretty bad. I’ve had chicks flap their wings in my hand and cover my hands with marching brown and red dots. (They don’t go for humans, but it’s still a stomach-churning sight.) So now there’s a lot of glove-wearing and glove-changing between nests.
And with that, back to work. To the mangroves!