托福official58听力lecture1 Homing Behavior in Birds原文解析+翻译音频

[00:00.00]NARRATOR: Listen to part of a lecture in a biology class.
[00:04.06]FEMALE PROFESSOR: So, those are some of the common theories on bird migration. [00:08.69]Now let’s talk about “homing.” [00:11.27]Homing is more than just the return flight home from migratory trips—homing can take place at any time and from any location. [00:19.36]It’s the ability that some birds have of finding their way back to an exact location regardless of their starting point… or how far away they are… or the time of year… and so on. [00:31.06]You’ve all heard of homing pigeons but there are lots of bird species that have highly refined homing skills so maybe there’s some evolutionary advantage. [00:41.44]Why would birds be so good at this? Todd?
[00:45.21]MALE STUDENT: Well, baby birds stay in the nest while the parents go out and hunt for food. [00:50.42]If the parents have to fly all over the place to find the food, they’d need to be able to find the nest again.
[00:55.86]FEMALE PROFESSOR:  And once you’d found food you’d want to get home quickly, wouldn’t you? To feed your young? [01:00.90]So you’d want the most direct path home—you wouldn’t want to retrace whatever winding, meandering path you’d taken while you were searching for food. [01:09.93]Being able to fly home directly is very efficient: the offspring get food faster and their parents are home sooner to look out for them.
[01:18.65]MALE STUDENT: But, it isn’t just the offspring that benefit—the adult birds get back to a safe place sooner as well.
[01:23.60]FEMALE PROFESSOR:  Right. Now, what about finding your way home after going south for the winter?
[01:29.11]FEMALE STUDENT: Well, it’d be nice if you could go back to a place you knew was OK. [01:33.82]Ya’know, one that’s got water or food… Not too many predators. [01:38.25]Some place where you might even still have a nest.
[01:41.30]FEMALE PROFESSOR:  Good. Now, so far, we’ve been talking about times when birds intentionally—or, at least instinctively—leave home, but are there other reasons why a bird might find itself away from its nest?
[01:53.99]FEMALE STUDENT: Birds are vulnerable to really strong winds. [01:57.33]Storms could blow them pretty far off course.
[02:00.31]FEMALE PROFESSOR: But finding your way back to your nest when you’ve been accidentally displaced is a little different from getting home after your annual migration to a warmer climate. [02:09.79]So, do you think all those mechanisms we discussed… that birds use when migrating… apply to homing as well?
[02:18.03]FEMALE STUDENT: I think so. I mean we talked about using the Sun and the stars as navigational guides—and that would certainly be helpful for homing. [02:27.34]And so would that ability to sense Earth’s magnetic poles—the one in the studies you described about the, uh, internal magnetic compass birds have. [02:37.73]Yeah, it should be the same.
[02:39.58]FEMALE PROFESSOR:  OK, so celestial bodies make good navigational aids. Anything else?
[02:46.26]MALE STUDENT: Well, for short distances, you could just memorize the area. [02:50.04]Use landmarks. Like, when my friend tells me to turn left after I see the post office to get to his house.
[02:55.87]FEMALE PROFESSOR:  So, when birds are out searching for food, they can memorize landmarks. [03:01.15]Mountains, rivers… who knows, maybe even the post office. [03:05.15]Studies of gannets have shown that this is one way they navigate. [03:09.27]Gannets are seabirds so when they wind up in an unfamiliar location over land, they fly in outward spirals until they reach the coast. [03:18.83]Then they use the coastline to find their way home.
[03:22.04]Of course, when we say that birds “memorize” their terrain—that may not be accurate. [03:28.52]It’s not always a good idea to use human analogies when trying to understand animal behavior—particularly when it comes to navigation which we, as a species, are spectacularly bad at. [03:39.80]I mean, even with maps, how often do we get lost? [03:42.62]But, with birds, they’re actually overengineered to be good at navigation. [03:48.03]Just think about all those tools we’ve discussed—celestial bodies, magnetic fields, landmarks—they’ve got a lot of sensory cues at their disposal. [03:57.77]But how do they use them? [03:59.65]For example: do birds use one navigational cue at a time… Like being guided by stars when the sky is clear and using magnetic fields when it’s cloudy? [04:10.28]Or, do they use all these tools simultaneously—calibrating their location from multiple cues at the same time? [04:19.45]Does the answer depend on the particular species? [04:23.27]This is a really rich subject for research… In fact, let’s talk about how you might go about designing some experiments to answer these questions. [04:22.04]Keeping in mind, as I said, that your personal experiences won’t be of much use as you try to come up with hypotheses to test.