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Short toed eagles migration question

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Offline Clive

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« on: March 19, 2007, 22:42 PM »
Hola,

I have given up for the time being posting silly pictures of plants for identification and now have something more profound to ask.

Short toed eagles, aguila culebrera, Snake eating eagles....

Nick can you post that cool video link here?

OK, so why are short toed eagles one of the first birds to return to our area of the Sierra de Grazalema. Reasonably high mountains with an average height I guess of 700 metres and peaks above 1400. (highest 1654)

First sighting this year 26th of February but all the snakes are still in hibernation or at the very least in short supply.

Why would a bird whose staple diet is reptiles evolve to be in an area when its food supply is not available?

Has the climate changed and the reptiles know but the bird hasn't adapted?

What is the snake eagle feeding on when it first arrives into the area? Its not snake that's for sure.

I have seen these guys many times with snakes in their mouths on the wing but I have never seen them on the ground with a rabbit or any other prey.

Any ideas?

Clive
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Offline Technopat

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« Reply #1 on: March 19, 2007, 22:49 PM »
Daft question - but mightn't they also eat lizards, etc. who must be rushin' round out in the sun?
How often do they need to eat - can they go for coupla days without food while they migrate on the off-chance that when they reach their destination and/or technical stopover there'll be summat to snarf?
Regs.
Technopat
Technopat's disclaimer: If this posting seems over the top and/or gets your goat (Sp. anyone?), please accept my apologies and don't take it personally - it's just my instinctive tendency to put my foot in it whenever/wherever possible. See also:
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Offline Clive

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« Reply #2 on: March 19, 2007, 22:57 PM »
Hola,

Oscillated lizards are out of hibernation like late march but only on warmer days.

The geckos are still sleepy and I don't think they are snake eagle food anyway

Smaller lizards are out and about on sunny days but again i think they are not snake eagle food.

What I am after is evidence of a snake eagle with a rabbit in its claws.

When they cross the straits they head North and the further north they go the more likely their food supply is still in hibernation?

Clive
« Last Edit: March 19, 2007, 23:17 PM by Wildside »
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Offline nick

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« Reply #3 on: March 19, 2007, 23:23 PM »
Can't work out how to embed video here - I presume it is possible

Anyway for now it's here:

http://www.iberianature.com/spainblog/2007/02/22/short-toed-eagle-video-2/

Enjoy
« Last Edit: March 28, 2007, 16:02 PM by nick »
Nick
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Offline nick

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« Reply #4 on: March 19, 2007, 23:39 PM »
Nick
http://iberianature.com/barcelona/history-of-barcelona/spanish-civil-war-tour-in-barcelona/
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Offline Clive

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« Reply #5 on: March 20, 2007, 13:52 PM »
Hola,

Getting back to short toed eagle migration and available food supply.

Is this something to do with climate change, whereby the reptiles are coming out of hibernation later but the birds are migrating like normal...

Clive
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Offline Jill

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« Reply #6 on: March 26, 2007, 23:07 PM »
I don't think I follow you there, Clive. If the planet is warming up, and the winters are getting warmer shouldn't the reptiles be coming out of hibernation sooner???
My geography is not good, but I think we're a tad further north than you, albeit at sea-level. I haven't seen any myself but a reliable friend (nature warden on one of the islands) tells me that the local snakes are around now. Maybe some of yours are too... (or is it snowing over there? No telly, so I never know what's going on anywhere else).

Jill

Offline Clive

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« Reply #7 on: March 26, 2007, 23:57 PM »
Hola,

You pose an interesting question there Jill. What is the difference between "climate change" and "global warming"? Global warming isn't really explained properly in the media

I don't think even the big guys who study this understand it but "global warming" doesn't necessarily mean long hot summers.

Right now (here in Grazalema) out side here it is around 8 degrees Celsius and weather patterns across the world seem to be acting a bit odd over the last 20 years or so.

Locally, our snakes are just waking up and now it just went cold again so they go back to sleep for a bit more.

The snake eagles have been back for a while now and I see no food source for them apart from rabbits. (But I have never seen a snake eagle on the ground with a rabbit).

I am sure that what makes a bird migrate is an inbuilt hereditary system that changes slowly year by year, whereas the hibernating snake pokes it's tongue out to see if "locally" it is time to wake up yet.

These too conditions make not be synchronised which is why I ask what is the short toed eagle eating in the Sierra de Grazalema when I know for a fact that most or all of the reptiles in the area are still sleeping.

It's an interesting subject, that's for sure.

Clive
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Offline Jill

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« Reply #8 on: March 27, 2007, 11:13 AM »
It would be interesting to know how long the eagles can go without eating. I've heard that a wren has to eat pretty much non-stop , just to stay alive. An emperor penguin, on the other hand, spends around 64 days standing on the ice waiting for his wife to come back and take over the baby-sitting. (Or rather, egg-sitting.)
I've watched albatrosses and other big sea birds hanging around on the wing for hours. I've never yet seen one catch ANYTHING ! What I'm trying to say is, perhaps a big bird which spends its time soaring, and which therefore uses very little of its own energy, can subsist on its reserves while it waits for the larder doors to open?
Even some very small birds, such as warblers, go very long periods without eating while they cross oceans - and, of course, they are not even able to rest; they have to keep flapping.
It's amazing what birds can do!

Having said that, I agree that the bird's migratory instinct probably cannot keep pace with rapid changes in the climate. Perhaps those eagles which arrive later will breed stronger, healthier chicks with an instinct to arrive later...
But there's another thing to consider: I don't know where the birds come from, but I suspect that they come at a certain time because that's the time when the food over there runs short, or runs away and hibernates.

All this talk of albatrosses and eagles makes me yearn to get away from La Manga, where the only things which soar are the jet planes and the mooring prices.

Jill 

Offline Sue

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« Reply #9 on: April 08, 2007, 22:53 PM »
Hi All

We watched a booted eagle stoop the other day and it flew off with a squawking snack from an area usually covered in small birds such as larks.
Having seen one with a young partridge and another with a rabbit last year I checked out their food supplies.
Booted eagles (Hieraaetus pennatus) prey on small to medium sized birds as well as ocellated lizards and rabbits. It does seem odd that these birds which are able to feed on such a variety arrive in Iberia later than the Short-toed eagles.

Short-toed Eagle - Circaetus gallicus, in southern Europe their prey consists of about 95% snakes, 4% lizards, and 1% mammals. These birds arrive early and in a cold snap such as we are having must find reptiles in very short supply. There is at least the ability to eat mammals although it did not mention species. Birds are apparently not on the menu.
(http://www.hawk-conservancy.org/priors/shorttoe.shtml)

Regards, Sue
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