|We needed to know how much we could trust the
information from the satellites, and checking the satellites' accuracy showed that even
the data of the lowest quality was still within about 10 km or so of the true location of
the bird. So we think the tracking data are reliable.
Drawing conclusions about our two hypotheses was not difficult. The satellite tracks all gave strong support to hypothesis 2, that parents fly all the way to Peru to find their food. None of the tracks gave support to hypothesis 1. So, we have a lot of confidence in hypothesis 2.
However, we only tracked five birds, and it could be that a larger sample would show that some birds do look for food within the Galápagos Islands, or even that some birds fly to other places that we do not suspect. Still, the simplest explanation for the results that we got is that most or all of the parent birds, including our tracked birds, go to the Peruvian coast for their food.
Why would they fly all that way? We don't know for sure, but you may find clues if you check Kids Using Satellites and ask what is different about that part of the ocean compared to the ocean in and around the Galápagos Islands.
And who are the birds that are seen flying around within the Galápagos Islands? We thought that they might be birds that are not nesting, so-called non-breeders. We put little plastic leg bands on some of these non-breeders in 1996 so that we could recognize particular birds, and we kept track of their activities. We found that when they disappeared on feeding trips they were only gone for a day or two. This is not enough time to get to the feeding spot near the Peruvian coast. The parents that we tracked took 4-5 days to reach that spot. So, if we review the facts, we see that:
From all of this, we suspect that the birds feeding in Galápagos are non-breeding birds, but we haven't yet done a good test of that hypothesis. How should we test that hypothesis if we are going to do it correctly?
And why don't the non-breeders go to the Peruvian coast with their breeding neighbors? We don't know....