Subject: [Tweeters] the weight that a predator can carry
Date: Dec 19 14:54:02 2012
From: Kevin Purcell - kevinpurcell at pobox.com


I think this came up a while back on Tweeters talking about Bald Eagles and the maximum weight they could lift from the water surface (and how far they could fly with it).

It's not just weight of the predator the wing loading of the bird is important too. The lower the wing load (weight per unit wing area) the higher the additional fraction of weight of prey that can be carried. Peregrines, for example, aren't really optimized for low wing loads.

I remember 50% of body weight as maximum rule of thumb for US eagles but I don't have a citation for that.

I see Wikipedia (that reliable source of info :-) has this too for the Golden Eagle (from Jeff Watson "The Golden Eagle". A&C Black. ISBN 978-1-4081-1420-9)

http://en.wikipedia.org/wiki/Golden_Eagle

> Most prey taken are around half the weight of the predating eagle, with a typical prey weight range of 0.5?4 kg (1.1?8.8 lb),[2] though this eagle will sometimes fly with prey equal to or slightly heavier than its own weight (4?7 kg (8.8?15 lb))


The Harpy Eagle (and the Philippines Eagle) are both forest monkey hunters that have been measured to carry 100% of their weight whilst flying. They have very accipiter-like wings (short wingspan but long chord) so I suspect they have low wing loading in normal conditions. See the article for citations.

http://en.wikipedia.org/wiki/Harpy_Eagle

> The Harpy Eagle has been recorded as lifting prey up to equal their own body weight.[4] That allows the bird to snatch a live sloth from tree branches, as well as other huge prey items. Males have been shown to focus on relatively smaller prey, with a typical range of 0.5 to 2.5 kg (1.1 to 5.5 lb) or about half their own weight.[4] The larger females almost invariably take larger prey, with a minimum recorded prey weight of around 2.7 kg (6.0 lb). Adult female Harpys regularly grab large male howler or spider monkeys or mature sloths weighing 6 to 9 kg (13 to 20 lb) in flight and fly off without landing, an enormous feat of strength.[4][22][28] Prey items taken to the nest by the parents are normally medium-sized, having been recorded from 1 to 4 kg (2.2 to 8.8 lb).[4]The prey brought to the nest by males averaged 1.5 kg (3.3 lb), while the prey brought to the nest by females averaged 3.2 kg (7.1 lb).[13]

Regarding my own observations I've seen Cooper's flying with Robins and Pigeons

450g Coop
77g Robin
270g Feral Pigeon (that's more than 50% -- I notice they tend to remove the head, often eating the brain and fly on without it attached which might bring the weight down)

The old vernacular name for the Peregrine was "Duck Hawk" -- I wonder which ducks they would take and fly with? Teal and bufflehead perhaps? Maybe a Wigeon?

720g Peregrine
1100g Mallard
720g American Wigeon
380g Bufflehead
350g Green-winged Teal

All weights from Sibley. It's not clear if these are averages or typical maximums.

So no bird is known to carry more than 100% of its own weight.

On Dec 19, 2012, at 1:13 PM, Dale C wrote:

> I once watched a peregrine falcon hit and kill a California gull. She (she was a female) flapped and flapped but could only slow and try to control their fall in the Yellowstone Canyon. She was unable to lift the gull once they landed. The next morning the gull had been taken up to a nest site in a number of pieces.
>
> According to Sibley, the gull's weight was about 80% of the weight of the falcon.

--
Kevin Purcell (Capitol Hill, Seattle, WA)
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