In last month’s post I wrote about spring being my favorite time of year and how great it is to see many birds that left, so many months ago, returning to breed or catch a glimpse of those passing through to points farther north. I touched a little bit on the subject of migration, and thought I’d expand on that a little more this month, as I’m sure that most of you have also been seeing new birds regularly for the first time this spring. I don’t know if everyone is like me, but when find a subject that interests me like birds, I sometimes go a little overboard and really try to learn as much as I can about the subject. And one of the things that I find utterly fascinating is avian migration. So for this month, let’s take a look at a few cool facts about some amazing travelers.
Many bird watchers are attracted to raptors, and while some species don’t migrate, many do. But did you know that very few raptors make significant trips over water? Most raptors rely on thermals, rising columns of warm air, to gain altitude with minimal flapping, conserving energy and allowing them to soar for many miles once the thermal dissipates after carrying them to great heights. Thermals aren't generally present over water, so for a raptor it is best to avoid water. I’ve read, for example, that raptors coming down the eastern seaboard will go the long way around the shores of Chesapeake Bay, a much greater distance, instead of flying over the bay. Swallow-tailed Kites are one exception to this rule, crossing more than 100 miles over the Straits of Florida to Cuba, then nearly 200 miles over the Gulf of Mexico to the Yucatan Peninsula before finally making their way overland to Brazil. Ultimately, this species flies over 4000 miles each way during their annual migration. Much of what we know about this species’ migration wasn’t learned until the late 1990s when satellite tracking devices that could be attached to the bird were first used.
|Swallow-tailed Kites (Elanoides forficatus) - note the difference in tail shape between the center bird, a juvenile, and the adult bird on the left.|
Many species of North American birds cross the Gulf of Mexico and take a much longer trip than the kite – it’s over 500 miles from the shores of Louisiana to the northernmost tip of the Yucatan. But to me the most amazing is the Ruby-throated Hummingbird. Though many Ruby-throateds travel overland through Texas and Mexico, large numbers of this tiny species (3 – 3-1/2 inches long and weighing 3-6 grams) make the long trip over the Gulf. It’s hard to imagine those tiny wings traveling so far without stopping – flight time is said to be about 20 hours!
|Female Ruby-throated Hummingbird (Archiochus colubris)|
Another tiny traveler is the Blackpoll Warbler, a species that breeds in the boreal forests of Canada and Alaska. Their migration route first begins with a trip east to New England or the Canadian Maritimes – and if breeding was in Alaska, that’s a distance of over 3000 miles! After a few weeks of “refueling” by eating lots and lots of insects, this little dynamo heads south, some flying over 2500 miles over the Atlantic Ocean before making landfall in South America! Interestingly, the trip north is mostly overland, though they still have to cross the Caribbean and/or Gulf of Mexico before traveling north through mainland North America.
|Blackpoll Warbler (Dendroica striata)|
Of North American breeding birds, a couple of sandpipers are recognized for their long distance travels. Red Knots breed in the Canadian Arctic and many of them travel all the way to the southern tip of South America (Patagonia and Tierra del Fuego). Though most of their 20,000 mile annual round-trip is made in 400-500 mile steps, the northbound trek includes a 3,000 mile flight over the Atlantic from Brazil to the shores of Delaware Bay. The Bar-tailed Godwit, a fairly large shorebird that breeds on the Alaskan Tundra (and one I’d really like to add to my lifelist someday), makes a southbound journey that is truly amazing. They fly for up to 8 straight days over the Pacific Ocean all the way to New Zealand, traveling over 7,000 miles - without stopping!
|Red Knot (Calidrus canutus rufa)|
To learn more about North American bird migration, I highly recommend Living On The Wind: Across the Hemisphere with Migratory Birds by Scott Weidensaul, my source for much of this information. Since it was written, ornithologists have added new tools (satellite tracking, for example) and the body of knowledge has expanded greatly, but it is still a great book that I have read several times.
Good birding and we’ll see you next month!