Since it’s time for the southern migration of the ruby-throated hummingbird here (North Carolina), and also hurricane season, I started worrying about the little guys making that looooong trip across the Gulf of Mexico. I know they’ve done well from an evolutionary standpoint ; the migration has coincided with tropical storms for a good long time, and there seem to be plenty of them making the return trip. How do they do it, though? Do they get stuck in storms in the middle of the Gulf, or can they gauge the weather enough to make a “decision”? How do the first time juveniles know?
This brings up another question. A lot of data must be obtained by banded birds. How exactly do you band a hummingbird?! Their legs are so tiny, and at such a small weight, any encumbrance would be a big problem in flight. How do your big ol’ fingers do it???
I saw a female RT today in the garden, so they haven’t all left. It boggles my mind that they can make the migration at all, but in the face of a hurricane, Yikes!
In both spring and fall, some Ruby-throats fly straight across the Gulf of Mexico from the southern U.S. to Yucatan. This takes 18-22 hours. Others follow the safer but slower route following the Gulf coast from or to Texas. Apparently, more birds take the coastal route in fall, perhaps because of the hurricane factor.
In any case, the hop across the Gulf only takes a day. Birds are pretty good at sensing barometric pressure, so an approaching storm would often give enough warning so that a bird wouldn’t launch out over the ocean if it sensed an approaching storm.
Also, the migration is spread out over several months. A hurricane might wipe out some birds, but it won’t threaten the survival of the species.
Regarding juveniles, as the site says they just follow the direction their instincts tell them to travel. They aren’t taught the route by their parents.
Before migration, Ruby-throats may double their body weight by putting on fat. In crossing the Gulf, they can burn up almost all of that spare energy supply.
Here’s a site that shows how hummingbirds are banded. Unlike standard bird-bands, these are not pre-formed. The numbers are stamped on thin aluminum sheets, and must be cut apart and formed by the bander.
When I did my thesis work on hummingbirds in Panama, I had to be able to identify individual birds. For larger kinds of birds, colored plastic bands can be placed on the legs. But hummingbird legs are extremely short and usually concealed in the feathers when birds are perched. What I did was cut strips out of thin acrylic plastic, and form a circular band at one end to go around the leg. This would leave a “tail” of colored plastic that would project beyond the feathers. I would glue the band part together, of course allowing sufficient space so as not to constrict the leg. This didn’t seem to bother the birds once they got used to it, and I observed some over many months. Eventually though, the glue would give way and they would shed the band. This wouldn’t be a feasible technique for migratory hummingbirds.
This guy temporarily color-marks hummers with harmless paint. I also did this as a back-up to color banding, but placed the color spots on the bird’s back where it couldn’t preen it out.
Speaking of migration, last year there were several hummingbirds in New York as late as the Audubon Christmas Count. I saw a Rufous Hummingbird at a feeder in Yonkers; a late Ruby-throat was also hanging out there. And there were not one, but two Calliopes visiting flowers in the garden at the Cloisters Museum in upper Manhattan. A friend of mine, who works with Audubon, was involved in a debate on whether to capture these waifs and keep them over the winter so they wouldn’t succumb to a sudden cold snap. At the end, it was decided to let nature take its course. They eventually disappeared, but no one knows whether they finally went south or froze.
Colibri, I looked at the first site before posting, so get the gist of it. Specifically, how do birds sense barometric pressure? Especially when gaugeing a long-distance flight? And, how can the juveniles possibly “know” the route(would appreciate any links to bird instictual behavior). Maybe it’s all just the long road to knowledge, but I still find it incredible that a 3 g bird has the wherewithall to fly hundreds of miles as a matter of course.
About the Rufous and Calliope being found outside of their normal range; is that because of a global warming trend, or because of human planting of exotic plants, or neither? So, what maps of hummingbird/insect food sources are available?
I hope I’m not asking too many ?, but, I am always agog at hummies.
Dumb follow-up question-- 18-22 hours? Ok, I can see an albatross or a pelican or gull or something like that doing this, with the whole cruising along drafting and gliding thing-- like riding a bike for a long time, but damn! Hummingbirds. . . they don’t glide much, do they? Is this why they can/ do drink/eat pure concentrated sugar-carbos or what? I’m just imagining that kind of metabolism for that duration. . .
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I remember reading once (long time ago!) about an experiment done with migratory birds. (don’t remeber the species) Eggs were hatched in a lab, and the chicks raised without adults. When they reached the juvenile stage they were put in a large dome, and stars were projected on the dome. The birds would orrientate themselves to the stars. The crazy part was, IIRC, that the birds seemed to have a genetic knowledge about which stars to follow. Colibri do you have any idea what I am talking about?
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Although it’s been established that birds can sense barometric pressure, especially throuigh work on pigeons (they can apparently sense a difference in pressure corresponding to a five meter change in elevation), the actual mechanism is not well known. It could have something to do with the air sac system they have throughout their bodies. After all, even humans can sense pressure changes crudely in a elevator or airplane when out ears pop!
Birds definitely time their big migratory jumps to avoid bad weather, and the most likely mechanism for this is the ability to sense falling barometric pressure.
Birds use a variety of systems to navigate. They are multiply-redundant, so even if one isn’t available (such as when the sky is overcast) they can fall back on others. Birds have been demonstrated to use landmarks, sun position, the pattern of polarized light in the sky, constellations (particularly the pattern of rotation), magnetism, and possibly even smell to find their way.
Some birds such as cranes and geese migrate in family groups, and others migrate in large flocks, and the adults can teach the young the way. However, many birds don’t, and the route is, at least in part, genetically programmed. As the article indicates, juvenile birds seem to have the general direction they should migrate “hard-wired.” And this direction varies depending on the geographical area the young bird was hatched.
Yes, it is incredible. As the first site I linked to says, hummingbirds can double their body weight and lose it again in the course of migration:
Of course, when these guys showed up in New York in December, everyone immediately said “Global Warming!” However, that may be a bit too facile. It’s hard to generalize from a few anomalous cases. These birds normally don’t occur east of the Great Plains (except for some Rufous along the Gulf Coast in migration), so they had their directions very badly screwed up. However, the fact that they had survived so far north for so long could have had something to do with milder temperatures (perhaps connected to global warming), people who had left their feeders up late, plus the availability of exotic plantings (and these may have also been blooming late due to milder temperatures).
The over-water gap they cross is 500 miles, and hummingbird flight speed is 25 mph, so it takes about 20 hours of continuous powered flight. Hummingbirds can’t glide any significant distance. Since Ruby-throats beat their wings about 55 times per second, a Gulf crossing takes about 4 milllion wing beats. This is why they lose half their body weight en route.
Hawks and vultures, on the other hand, use a very low energy migration strategy. Broad-winged and Swainson’s Hawks and Turkey Vultures migrate from North to South America in enormous flocks that rely on thermal soaring. (A few years ago I ran a project that counted 1.5 million birds migrating through this part of Panama. Some days I can see 40,000 birds pass by my office window.) These birds scarcely need to flap their wings at all during the several months it takes to migrate. However, they also apparently don’t eat en route, and also lose much of their stored fat on the journey.
Yes, the article I linked to two posts up mentions this. In fact, I’ve seen some recent work that indicates, if you take birds from different parts of the species range, that have different innate migration vectors, and cross them, the offspring will have an intermediate vector. Sorry, I wasn’t able to find a reference to this on-line.
Colibri, Thank you for the link. Fascinating stuff. I wonder what it must ‘feel’ like to have such hard wired instincts. Imagine if you were a child and when someone handed you a shoe and you knew exactly what to do with it even though you had never seen a shoe before. Not exactly the same thing, but similiar in a way. Thanks again,
Rhum
I just want to point out that the spring migratory pattern of RTs from Mexico to the US is in March, before the hurricane season, which begins in June and ends in November. I assume the fall migration is primarily before the end of November, but at least they don’t have to worry about hurricanes in the spring, and hurricanes are rare after September. What are the dates for the fall migration?
The first site I linked to mentions this. The first males begin to migrate south as early as mid-July, and the peak is late August to mid-September, essentially the middle of hurricane season. The article says that more birds follow the Mexican coastal route in fall than in spring, perhaps because of this very reason.
Stares ruminatively at the hummingbird feeder, recollecting admonishments to keep filled on a regular basis . . .
Problem 1: If hummingbirds can double their body weight, why don’t they stock up at the feeder when it’s available, instead of taking a chance, once every hour or so, of happening to come back when there’s nothing left – or that a hostile hummer might catch them?
Problem 2: Is how much gliding they do so much the issue as how well they can glide? Something that’s airborne with no glide must sustain its altitude constantly, or they fall like a rock. The better the glide ration, proportionately the less effort is taken covering a distance.
Problem 3: A bird over land could easily see that it was following a favorable wind. I’m not sure how a bird over the ocean could, but . . . seems like a hummer would if it could.
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