The Galapagos islands are famous for their association with Charles Darwin and the theory of evolution by natural selection. Being isolated, the islands acted much like a controlled laboratory for clear observation of basic evolutionary adaptations among species.
Within the Galapagos also live species which have not yet had their evolution defined by the islands’ environment. Interestingly, they may be relying on some more deep-seated and complex survival strategies.
Blue-Footed Boobies are large sea birds that live in the eastern Pacific ocean. They’re tropical. They’re fish-eating.
That’s Doctor David Anderson, professor of Biology at Wake Forest University, here in Winston Salem. He has been studying Blue-Footed Boobies since the early 1980s. Along the way he found that an interesting thing was beginning to happen to these birds.
We had a healthy population of blue-footed boobies there. They appeared every year. They produced offspring every year. And then in 1997 that stopped and we didn’t see them again in any kind of meaningful numbers. That was a clue that some issue was happening. We noticed a breeding problem but we didn’t notice a mortality problem. We don’t see dead birds laying around.
Dr. Anderson and his team set about several studies to figure out why this was happening, and have come down to one likely hypothesis.
So in 2011 we started a two-year study looking at breeding biology across the whole place, all the major colonies, and found that indeed they’re not breeding. They sometimes attempt, not as much as you would expect, and when they attempt they pretty much always fail. They show that they’re interested in breeding with courtship behavior. That’s one thing blue-footed boobies are famous for. The blue feet are about impressing the other sex. They do a lot of trying to impress each other but they decide not to actually go through with reproductive attempt. So they’re not producing young individuals to replace natural deaths of older individuals. Our accounts indicate that the population size is only about one-third of what it was in the early 1970s. A simple population model suggests that it’s just due to failure to breed. We think it’s a food supply problem. These guys, in the past when they were breeding well, focused on a particular fish species which is a sardine — a really rich food source. It’s high in fat, so lots of energy. When you find one sardine you find lots of them because they school. But now we find not nearly as much sardine as we did in the past. They’re still finding some but they’re not getting enough to actually go through with the breeding attempt. We think that the sardine availability cycles on a very long period, and we have evidence from nearby that this is true. That when sardines are common for about twenty or thirty years another kind of fish, anchovies, are not so common and vice versa. However in Galapagos we don’t have the anchovies to take the place of the sardines.
Boobies on the mainland of South America do indeed thrive on anchovies when sardines are not plentiful. But the Galapagos population is denied this alternate food source, according to Dr. Anderson.
The driving purpose of all life is to reproduce. Clearly you can’t reproduce if you don’t survive. A couple billion years of survival have built in some interesting evolutionary methods of coping with hard times and Dr. Anderson believes the Boobies are using one of these strategies. Its like waiting for financial stability before having kids. Sort of…
We speculate that it has to do with not so much raising a chick, but it’s more about later, when a recently independent offspring has to forage for itself, but it’s a boneheaded teenager basically, and it struggles to deal with a difficult environment. We think the parents are abandoning reproductive attempts because they’re predicting in five months there’s not going to be enough sardines for their juveniles to be able to make it, so why invest in an offspring that is not going to be able to actually survive later on.
Does this all mean that the Galapagos Blue-Footed Booby is headed for extinction?
We don’t think that they’re never going to breed during these poor conditions; they may get a little bit of breeding done. I think it’s unlikely that we’re going to see the extinction of this population due to this cycle. But if you overlay onto this natural problem some sort of human-caused problem, then it could possibly tip them over the edge.
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