Once again we’re lucky to have a video sent by a reader. Dennis Hansen, a biologist at the Institute of Evolutionary Biology and Environmental Studies in Zurich, has sent us pictures and videos before from islands in the Indian Ocean. Here we have a reptile from the Aldabra Atoll, with these notes:
I am slightly disturbed and sorry that you’re stuck with watching feline GIFs, though, when everyone knows that visual chelonian treats are so much more relaxing. I hence rush to bring you some much-needed reptilian diversion. I just uploaded a video from last year on Aldabra, which was a very wet year indeed. It shows a first bobbing, then swimming Aldabra giant tortoise, Aldabracehlys gigantea, in a pond on Eastern Grand Terre, Aldabra Atoll. Note how the tortoise’s stride changes when it hits slightly deeper waters & can’t bob on the bottom anymore.
I wasn’t aware that the Aldabra giant tortoises (Aldabrachelys gigantea; see Hansen’s other photos of these remarkable reptiles here) could swim. Like the Galápagos giant tortoise, they are the enlarged descendants of a lineage that managed to make it to this remote atoll. See them getting a bath and a scrub here.
Here’s a photo from Wikipedia of Eastern Grand Terre, which the site describes as:
. . the world’s second largest coral atoll [154 km²]. It is situated in the Aldabra Group of islands in the Indian Ocean that are part of theOuter Islands of the Seychelles.
Uninhabited and extremely isolated, Aldabra is virtually untouched by humans. It has distinctive island fauna including the Aldabra giant tortoise (Aldabrachelys gigantea). It consists of four islands around a large shallow lagoon, encircled by fringing coral reef. The atoll reflects both fossil and geomorphological features, the former is the source of the biodiversity seen today. The atoll has the largest population of Giant Tortoises in the world (about 100,000 animals). Sir David Attenborough called Aldabra “One of the wonders of the world”, and it is also known as one of “crown jewels” of the Indian Ocean. Aside from its vast population of tortoises, it is also the largest raised coral reef in the world with an elevation of 26 feet (7.9 m); and the second largest atoll in the world after Kiritimati Atoll. Aldabra has a large population of the world’s largest terrestrial arthropod, the coconut crab; and hosts the Aldabra rail, the only surviving flightless rail species in the Indian Ocean.
I must get there some day. . .
I’ll also put up about half the remaining photos I have from photographer Colin Franks (website here, FB page here), and hope that he’ll come through with other batches in the future.
Red-tailed Hawk, Buteo jamaicensis:
Red-winged Blackbird (female), Agelaius phoeniceus:
Red-winged Blackbird (female):
Bonaparte’s Gull, Chroicocephalus philadelphia:
Northern Flicker, Colaptes auratus:
nice pics,
the gull is not a Bonaparte’s Gull though, but a Mew Gull (Larus canus, sometimes also called Common Gull).
I think this is the green pond on google maps (https://www.google.com/maps/place/Aldabra+Atoll,+Seychelles/@-9.4121885,46.5080107,475m/data=!3m1!1e3!4m2!3m1!1s0x227a31df5a3f0a6d:0x36f70a2fb20bc754)
Quite close 🙂 – it’s actually this one, which in the dry season of the google image is reduced to a small pool of sludge: https://www.google.com/maps/place/Aldabra+Atoll,+Seychelles/@-9.4261911,46.506542,224m/data=!3m1!1e3!4m2!3m1!1s0x227a31df5a3f0a6d:0x36f70a2fb20bc754
Hey thanks, I wasn’t expecting that. 🙂 I see the actual location is closer to the ocean. Very interesting video and info. Thanks!
Most welcome; thanks for the kind comment.
really nice shot of the flicker in flight
I like the red-winged blackbird shots also, as one rarely sees the females.
Really all the shots are good.
Great photos, especially the Red-tailed Hawk!
Such handsome bird pictures!
What is it about evolution of giant tortoises on islands? I think I had read somewhere that the tendency for them to become large on islands could be from a combination of selection for reproductive success (bigger is more successful) plus a release from constraint to be large since islands do not have predators against big animals. Continental tortoises would be easy prey from large predators.
Nonetheless there were continental species of giant tortoise. They seem to disappear from the geological record about the same time that the genus Homo was spreading out over the continents.
Exactly – there used to be large & giant tortoises all over the place. For example, where I live now, in Switzerland, there used to be 1.5 m long giants with enormously thick shells, until a few million years ago. And India & other places of course used to be home to Colossochelys atlas – a 2-m long mega-tortoise – which, as you say, died out just coinciding with the first hominids making their way out of Africa.
So that seems to mean that the giant tortoises are another megafauna that we may have hunted out of existence! I thought that gigantism in tortoises was just an island thing.
Well, good to know, and thanks!
Well, I think that insular giant tortoises are doing what you describe in your first post, to some degree – insular gigantism in reptiles is common, and giant tortoises can sustain quite large populations even on small dry island because their energetic requirements are small. Mammals, with higher energy requirements, can’t maintain high insular populations. On the other hand, tortoises reach oceanic islands by overwater dispersal, which is probably only feasible for fairly large tortoises, so insular tortoises may have a head start.
The Galapagos species’ closest relative, as I recall, is the South American yellow-footed tortoise, which gets pretty big – not Galapagos-big, but a really big adult gets to be close to a metre in length. Something this size could conceivably survive being swept out to sea and drifting for weeks or months before coming ashore on the Galapagos. A smaller tortoise would likely not be able to deal with being immersed in salt water for the necessary length of time.
Fascinating stuff, thanks!
I think that blackbird’s an accommodationist!
🙂
“… Colin Franks (website here, FB page here), and hope that he’ll come through with other batches in the future.”
Second that! Really super photos Colin.
I’m kinda proud to say that I was able to identify the red-tailed hawk and the female red-winged blackbird. I was able to guess that mainly from how it’s standing on the reeds, which is almost always how I see them perched.
The gull I didn’t get, being an inlander, I hardly ever get to see gulls.
I also didn’t get the flicker, but that side view is one I hardly ever see. I can usually see them when they’re startled and flying away, when they can be ID’d by their white rump:
https://c1.staticflickr.com/3/2614/4032600204_15edcbe580.jpg
Wonderful shots, all!
Marvelous photos! I didn’t know the female red-winged blackbird looked like that. I have them in the garden, both male and female (now that I know).
Speaking of turtles/tortoises, check out this 90lb fella, an alligator turtle.
http://www.youtube.com/watch?t=222&v=WT2eLretCWE
Alligator snappers are awesome beasts! Thanks for the link.
That tortoise is really moving. Thanks for the extra links as it is hard to see what the tortoise actually looks like from the video. I’ve never heard of this tortoise or of the atoll where it lives. I fear for atolls across the planet as sea level rises; it could mean the loss of some real treasures.
Spectacular bird photos too! Vivid, top-notch quality.
Yes, I think you are right about the effect of rising sea levels. We should move to rescue some of these unique species.
There was a recent news story about an Aldabra tortoise which had apparently drifted with the ocean currents to East Africa. It landed on the coast and did not appear to be any the worse for wear. I’m inclined to believe this story because, in the photo I saw, the tortoise’s legs and lower shell were covered with barnacles. If it is true, this has bearing on how big tortoises got to oceanic islands.
That’s really cool!
Yes, indeed – that story was published (with the photo of mollusc-covered tortoise & all) in Journal of Natural history: Gerlach J, Muir C, and Richmond MD (2006) The first substantiated case of trans-oceanic tortoise dispersal. Journal of Natural History 40:2403-2408
Thanks, Dennis, that’s it – should have realized that it was in the professional literature, I was scanning elsewhere for it.
Nice videos and pictures. I think the lady blackbird is a bit embarrassed to have been caught in an awkward position. Fabulous flying flicker!
Very beautiful photos Colin, thanks!
If I’m not mistraken, the tortoise is wading, not swimming; it keeps its head above the surface at all times. Is that an accurate observation, and is there any significance to it?
b&
My tortoise used to bob in the water. He was very floaty.
I was noticing that, too…I don’t think the one in the video could dive, even if it wanted to.
Which puzzles me a bit, because I understand that the tortoises native to the Sonoran Desert here are prone to drown in backyard habitats if you don’t keep them away from too-deep water.
b&
My tortoise did drown in a backyard pond but we think he was getting a bit confused in his old age. He didn’t go near water normally (unless we washed him in the tub) but he had take to wondering around doing odd things like that. He was over 40 and I don’t think those tortoises live much longer than that. I almost think he was suffering from dementia.
I’m guessing that washing a tortoise in the tub might have depended more on the (young) age of those washing it than the hygienic needs of the reptile….
b&
Oh no, tortoises get dirty. They walk in food when they don’t want to eat it an poop all over the place so a nice bath is a good idea every now and then. The tortoise liked it too.
Now I’ve got mental images of the tortoise getting a good scrubbing with a toothbrush and maybe taking swipes at the rubber ducky floating amidst the soap bubbles….
b&
A good soak is a recommended part of tortoise husbandry. We generally keep them either in small spaces, in which they can end up walking through their own poo, or at least in places where they don’t have a handy stream or puddle in which to soak themselves.
It also helps with tortoise constipation. Srsly.
Yes, tortoises like to poop in water.
…for that matter, so do humans….
b&
Do they ever! SO many water changes…
What is your definition of swimming, Ben?
Hmm…in this case, I was looking for a distinction between full-immersion underwater movement and something that permits constant access to the atmosphere for breathing. I think “swimming” can reasonably accommodate that…?
b&
Sounds like you think dog paddling isn’t swimming?
Don’t we usually distinguish dog paddling from “real” swimming?
b&
Not as far as we’d distinguish it from wading, I’d say. 😀
I wonder if there’re regional / cultural differences at play….
b&
That, or Ben v. rest of world differences.
😀
…wouldn’t be the first time….
b&
If only someone else would wade (or breaststroke, as Ben would have it) in.
“…wouldn’t be the first time….”
Well, it’s a good thing not to run with the pack.
It starts bobbing, then, at the last part of the video, it is clearly swimming when it reaches deeper water. Aldabra (& other large) tortoises are very buoyant (lungs are located right underneath the top of the carapace), and will float quote high in the water without any effort at all. That’s how they got to so many islands in the first place. Before we ate them all out of existence, that is.
I like the female red winged blackbird precariously holding on to two reeds. They have such spindly legs, I don’t know how they avoid ripping them right off.
It seems “fun” for the tortoise to be able to move so quickly and effortlessly in the water, being that they’re so ponderous on land.
Just looking at that atoll, it would seem fresh water might be in short supply from time to time.
I love that, too! -sort of “hey! Lookit me legs! Wooooooh!”. But yes, the atoll is naturally very dry half of the year, and with global change it’s getting drier still. Too much water on one hand (rising sea levels), too little on another…