Melinda Conners, on Tern Island, Hawaiian Islands National Wildlife Refuge -- Masked and red-footed boobies on Tern Island have just started laying their eggs. They start breeding slightly later than black-footed and Laysan albatross.
They manage their eggs differently, too. In fact, masked booby chicks engage in a strange siblicide. Masked boobies lay two eggs per nest. If both hatch, the older, stronger chick usually kills the younger, weaker one. Dave Anderson, a TOPP researcher at Wake Forest University, has studied masked boobies for most of his career. In an episode of Scientific American Frontiers, he and host Alan Alda talked about why this siblicide works for masked boobies, and what happens if there's no siblicide. Here's part of the transcript:
DAVE ANDERSON: In terms of natural selection, selection is going to maximize the excess benefit over the cost. Certainly the benefit has to exceed the cost. In this case, there's a benefit to laying the second egg because they have lousy hatching success. They only hatch about 60% of the eggs, even if you eliminate accidents and stuff. Something about fertility or embryo development causes 40% of them to die. So if you're going to get one chick, gotta have one chick, you're prepared to pay the price of a second egg, even though it's expensive, because if the first one fails, the second can take its place.
ALAN ALDA: It seems to me that once you've gone to the trouble of laying two eggs, and you have a good shot at having two healthy adults come out of that, isn't your purpose better served to let both of them live?
DAVE ANDERSON: Yeah, good question. If you experimentally stop the siblicide from happening, and make them play nice, and then challenge the parent to bring back enough food for two, about 30% of the time, they can do it. She doesn't stop feeding. If there are two chicks in front of her, she'll feed 'em, you know, open mouth, put in food, that's what she does. And if there are two of them there, she'll put it in at twice the rate. So you say, well, they definitely should be stopping the siblicide from happening. However, if you follow those parents another year, you find out in the year after they raised two chicks, they take it on the chin in terms of survival. Particularly the moms. Regular moms survive at about 92%, from year to year. And the experimentals, that have had to raise two chicks, survive at about 75%. And that's a huge cost.
ALAN ALDA (Narration): A cost that in terms of natural selection simply cannot be sustained.
Red-footed boobies lay one egg. If that one is lost, they can lay another. Neither masked nor red-footed boobies have a brood patch -- an area of featherless skin with lots of blood vessels at the surface, so that heat transfers efficiently from parent to egg. So, they incubate their chicks with their feet! Males and females share egg-warming duties.
Masked booby sitting on two eggs. Since boobies don't have brood patches, the bird curls its feet against the eggs to keep them warm.
These two species of boobies look for food close to the island. That's much different from the albatross, who fly long distances to the more productive waters of higher latitudes. (You can check out the animated map of the black-footed albatross to see where the birds that are now tagged are flying, or the maps in the TOPP Data section.) Boobies feed mostly on flying fish, flying squid, sardines and anchovetta. They rely on schools of dolphins and tuna to scare their prey to the surface of the water, where they go after their food by plunge-diving, sometimes as deep as 98 feet.
Two white red-footed boobies with frigatebirds looking on.
We'd like to do a tracking study on Tern Island's other species -- including red-footed boobies and greater frigatebirds -- to complement our tracking study on Laysan and black-footed albatross. If we did that, we'd gain a better understand of the foraging strategies of seabirds within the waters of the Northwestern Hawaiian Islands Marine National Monument.
The Hawaiian Islands National Wildlife Refuge is part of the Northwestern Hawaiian Islands Marine National Monument, created in 2006. The largest marine protected area in the world (it's larger than 46 of the 50 U.S. states), the park was renamed Papahānaumokuākea Marine National Monument by Hawaiian natives. In the traditional Hawaiian stories, the goddess Papahanaumoku (Pāpā for short) gave birth to the islands.