OFFICIAL47 According to the professor, what helps albatross chicks survive despite the fact that their parents have to fly such long distances to find food? [ Click on 2 answers.]

[00:00.00]NARRATOR: Listen to part of a lecture in a biology class.
[00:03.87]FEMALE PROFESSOR: Now usually when we talk about birds flying long distances, we're discussing seasonal migration. [00:10.92]But there're some species that fly long distances not as part of a migration, but as a part of their regular foraging for food. [00:19.85]A great example's the albatross.
[00:22.20]Albatross are seabirds that nest on islands, and uh, and forage for food out in the open sea. [00:30.30]And you have one species that forages an average of a thousand miles from its nest. [00:36.10]And I read in another study where one albatross left a chick in its nest and went out in search of food, [00:42.74]and by the time it got back to the nest, it had flown nine thousand miles. Yes, Bob.
[00:49.42]MALE STUDENT: Um.… but why don’t they just build their nests closer to their food supply? [00:54.60]I mean, for one thing, they must burn up a lot of energy flying back and forth, and also, if the parents’re gonna have to be away from the nest that much, [01:03.74]aren't the chicks going to be pretty hungry most of the time?
[01:06.48]FEMALE PROFESSOR: OK, good question. [01:08.21]The chicks are capable of going for long periods of time without food, [01:12.73]which works out nicely since, as you point out, they may not get to eat that often.
[01:18.11]As far as the parents go, well, um, first, they typically can't get enough food in a single location. [01:26.10]So they have to visit several places on the same foraging trip, [01:30.49]and the locations of good foraging grounds tend to be very far apart.
[01:35.56]Uh second, they can't always nest on an island that's closest to the best feeding ground because some of those islands have too many predators on them—[01:44.75]predators that would just love some little chicks to snack on. [01:48.70]So I don't think they have much choice.
[01:51.93] But it still works out, because albatross fly using a technique called “dynamic soaring,” [01:58.07]which enables them to cover very long distances while expending very little energy. [02:03.64]If it weren’t for that, you'd be right—[02:06.12]they would probably burn up all their energy just flying back and forth.
[02:10.19]Another factor is, albatross lay only one egg at a time, [02:14.48]so when the parent returns with the food, that one chick doesn’t have to share it with a lot of other chicks. Yes, Nancy.
[02:22.32]FEMALE STUDENT: So you're saying that they might easily fly a thousand miles over the open ocean when they’re looking for food.
[02:29.16]FEMALE PROFESSOR: That's right.
[02:30.20]FEMALE STUDENT: Then how do they know how to get to the food—[02:32.97]I mean, which direction to take to get to the food—and how do they find their way back home?
[02:38.09]FEMALE PROFESSOR: Good point. And the truth is, we’re not sure. It's very difficult to keep seabirds in captivity, where you can study them, [02:46.92]and it’s very difficult to study them in the wild, you know. [02:50.21]But we think that a lot of what we’ve learned about songbirds probably applies to seabirds as well. [02:56.80]So we're thinking that albatross could make use of two different kinds of “compasses,” if you will: a magnetic compass and a celestial compass.
[03:06.83]The magnetic compass somehow makes use of Earth's magnetic field, much the way a standard compass does. [03:13.41]But to prove this, we would have to find some kind of magnetic sensory organ in birds. And we're not sure that we have. [03:21.51]We… we have found in birds a mineral called magnetite, which we think might be somehow related to this, because magnetite is a natural magnet. [03:32.27]But the problem is that we’ve also found magnetite in nonmigratory birds, which suggests that it may in fact serve a completely different function, not related to navigation at all.
[03:43.87]Um, and the other “compass,” the celestial compass, makes use of the stars, more or less the same way humans have historically used the stars to navigate in the open sea … [03:55.49]So that’s the way we think albatross navigate …
[03:59.48]So anyway … You know, think about it, how about if you had to go a thousand miles every time you wanted to get a bite to eat?
[04:08.14]FEMALE STUDENT: Yeah, and we complain about having to walk all the way across campus to get to the cafeteria.
[04:13.21]FEMALE PROFESSOR: Yeah.