Readers’ wildlife photographs

April 18, 2015 • 7:45 am

As I’m away, and my folder of readers’ photos is in Chicago, we’ll have only four pictures today, all of which were sent yesterday. Stephen Barnard in Idaho sent two pictures of a Swainson’s Hawk (Buteo swainsoni).

These hawks migrate all the way to Argentina. This is the first I’ve seen this season.

RT9A0498

Swainson's Hawk

I don’t know much about raptors, but I wasn’t aware of any in North America who migrate this far. But, sure enough, here’s the range map from the Cornell site. And they do make that long journey:

bute_swai_AllAm_map

And here’s some fun facts about the species, taken from Wikipedia:

This species was named after William Swainson, a British naturalist. It is colloquially known as the grasshopper hawk or locust hawk, as it is very fond of Acrididae (locusts and grasshoppers) and will voraciously eat these insects whenever they are available.

Their breeding habitat is prairie and dry grasslands in western North America. They build a stick nest in a tree or shrub or on a cliff edge. This species is a long-distance migrant, wintering in Argentina; it has been recorded as a vagrant in neighboring Chile, in the island countries of the Dominican Republic, and Trinidad and Tobago, and in Norway.

This species or its immediate predecessor is the ancestor of the Galápagos hawk, as demonstrated by recent research. The latter diverged from the mainland birds perhaps 300,000 years ago, a very short time in evolution.

The Galápagos hawk (Buteo galapagoensis) is a rare species (ca. 150 pairs) endemic to the archipelago. Given its geographic isolation, can we really say it’s a different species from the Swainson’s? (I’m adhering to the Biological Species Concept, which sees different species as populations that have genetically based traits that prevent them from producing fertile offspring.) I think so, as the migratory (and non-migratory) habits, which are probably genetically based, keep the species from meeting each other, and that is a form of either ecological or behavioral isolation. The species almost certainly resulted from one or more stray ancestors of the Swainson’s hawk that found their way to the archipelago several hundred thousand years ago. That’s plausible because, as you see above, individuals sometimes go far off course.

From John Harshman, who lives in the San Francisco Bay area:

From my back yard. First, a female (I think) Anna’s hummingbird (Calypte anna) coming in for a drink. I really like the feet. Second, a male rufous hummingbird (Selasphorus rufus) in mid-slurp. Both partaking from bottlebrush (Callistemon) flowers; I don’t know the species, but the genus is an Australian endemic. New camera (Panasonic FZ200).

Anna%27s on bottlebrush

male rufous on bottlebrush

19 thoughts on “Readers’ wildlife photographs

  1. Interesting info about the hawk. Makes one wonder what the advantage to such a long yearly journey is to favor it over those who would wander less.Maybe they just don’t like the cold 🙂

    1. Plus the hawk doesn’t seem to hang around anywhere year long. Always on the move, that hawk. It’s like the raptor version of The Littlest Hobo.

    2. As a grassland species specialising on grasshoppers and locusts it would need to head south from, at least, the northern part of the breeding range in order to find food in the winter. Once into south America it would then be obliged to fly beyond the forests of the tropical region to reach grassland habitats beyond.
      I suppose that it might find suitable food to the north of the tropical forest zone but as it is a soaring species that uses thermals to gain altitude, the energetic costs of the long migration are perhaps relatively low and thus it is worthwhile flying on to richer feeding grounds on the Argentinian steppes.
      All complete speculation on my part which may be completely off-beam. What I can say with confidence, however, is that it is a very handsome species that Stephen has photographed with his customary excellence.

  2. William Swainson got around the globe quite a bit, and we have one bird species here in South Africa named after him. Swainson’s Spurfowl (Pternistis swainsonii.
    I always thought the purpose of migration in birds was to find the best food sources. I don’t think the cold is really a factor, rather abundance or lack of preferred food.

  3. I’m hoping to see hummies back here in the next few weeks. Lovely hummie in the photo and very pretty bottle brush plant which I’ve only seen in New Zealand or Australia.

    The spring peepers and wood frogs are croaking up a storm here at night so hummies should be on their way!

    1. We have a lot of varieties of bottlebrush in New Zealand, but most are introduced from Australia. A beautiful native tree though with a similar feathery type flower is the Pohutukawa (poe-who-two-car-wah).

      We don’t have hummingbirds in New Zealand, but we do have native nectar eaters.

  4. Beautiful Swainson’s Hawk photos; you really captured a beautiful pose in that first shot. The head feathers are so perfect it may have just come back from the feather salon 🙂

    I was born in San Jose and lived there until I was seven. My first memory of hummers was seeing them drinking nectar from that same flower. What is that plant called again? Those flowers would attract all sorts of hummers and insects. I wish they grew where I lived now, but it’s too cold in the Winter.

  5. Gorgeous pics both of you.

    I always wonder why and how a bird would have evolved to go so far from summer to winter and back again. I would have thought there were better options.

    1. As mentioned in some of the comments above, it’s generally all about food. Throughout much of the temperate zones on each side of the equator, food is a seasonal resource. Insects emerge, plants produce seeds and fruit, mammals and reptiles and amphibians come out of hibernation as soon as it is reliably warm enough to do so. So for part of the year there are abundant resources to be exploited.

      But when the cold and short days set in, organisms have to adjust; many plants go dormant, animals hibernate, and insects pass the winter in life stages–eggs, buried larvae, cocoons–that reduce their metabolic needs.

      Many birds took advantage of their heightened ability to travel to move off to climes where the food resources are still abundant, hence the long north-south migrations.

      The much greater landmass north of the equator results in much greater resource blooms in the warm months, providing the extra resources birds need to raise their young, so most migrants nest in the north and “winter” down south in the southern hemisphere’s summer.

      In between there are sub-tropical and tropical species with either much reduced or absent migratory habits.

      (There are also boreal species that summer in the subarctic and winter in southern Canada & the northern US–or the equivalent locations in the eastern hemisphere.)

      That would be part of the “why”–the “how” is a bit more complicated but there are quite plausible hypotheses.

  6. We used to have a bottlebrush in our front yard. They’re lovely, especially when they are flowering and you can slap nectar out of it.

  7. Such a delightfully contrasting pair of taxa! IIANM, the hummers are every bit as fierce as the hawks. 🙂

    (Reminds me of this: birdandmoon.com/images/evolutionsucks.gif )

    1. Oh yes hummingbirds are little monsters. It is adorable how they can be so delicate yet so violently pissed off all at once.

Leave a Reply