Hawks and yellow legs (1 Viewer)

[ChrisKten]

I see a lot of Sparrowhawks in my garden, and something has always confused me. You can look straight at a Sparrowhawk in a tree, and due to the plumage, you've no idea that it's there. It's only when it moves that you see it. However, sometimes you see it due to the yellow legs and feet, as yellow stands out against the foliage.

So I was wondering why a bird that needs to hide in a green/brown habitat before launching an attack, evolved to have yellow legs/feet. Obviously it doesn't affect their hunting, and even Falcons have yellow feet/legs (Kestrel can also hide before attacking; they don't always hover), Buzzards too.

All I can think of is that other birds don't see the yellow as we do, maybe it's shielded in Ultraviolet?

 

[ChrisKten]

Nobody has a view on this?

 

[perlin]

I think it helps to see its tools of its trade,talons,and help it guide them,just a thought.

 

[fugl]

I think it helps to see its tools of its trade,talons,and help it guide them,just a thought.

Interesting idea. Another one along the same lines is that the bright color makes the BOP less likely to bite its own feet/legs while feeding.

 

[ChrisKten]

Thanks for the replies; that's two possibilities that I hadn't really considered.

I was also wondering if, instead of being "shielded" in the Ultraviolet (which Birds see, but we don't), perhaps the yellow somehow confuses the prey in Ultraviolet. The yellow feet are often the first thing the prey sees as the Hawk swoops at them, although not the last thing they see|=)| Also, there's the yellow Cere to consider. Sparrowhawks, for instance, incapacitate (sort of knead until the prey stops moving too much) with the Talons, but they also pluck at the same time. So I'm wondering if the yellow Cere serves a similar purpose to the yellow legs/feet.

 

[fugl]

I was also wondering if, instead of being "shielded" in the Ultraviolet (which Birds see, but we don't), perhaps the yellow somehow confuses the prey in Ultraviolet. The yellow feet are often the first thing the prey sees as the Hawk swoops at them, although not the last thing they see|=)| Also, there's the yellow Cere to consider. Sparrowhawks, for instance, incapacitate (sort of knead until the prey stops moving too much) with the Talons, but they also pluck at the same time. So I'm wondering if the yellow Cere serves a similar purpose to the yellow legs/feet.

You make some interesting points. However, to rain on your parade a little, many birds have bright yellow nuptial plumage & it's hard to believe that yellow is inconpicuous or confusing to their eyes. And I don't know why a bird's ability to see ultraviolet should affect its perception of other colors in any way, any more than seeing green should affect its perception of red. But then again I'm no scientist & nature is full of surprises.

I wonder if there's anything in the technical literature about any of these questions?

 

[ChrisKten]

You make some interesting points. However, to rain on your parade a little, many birds have bright yellow nuptial plumage & it's hard to believe that yellow is inconpicuous or confusing to their eyes. And I don't know why a bird's ability to see ultraviolet should affect its perception of other colors in any way, any more than seeing green should affect its perception of red. But then again I'm no scientist & nature is full of surprises.

I wonder if there's anything in the technical literature about any of these questions?

I just did a quick search, and it seems likely that we just don't know yet. It also seems likely that yellow doesn't even look yellow to a bird.

I found, what seems like, a proposal for research into Birds' colour vision (http://www.bristol.ac.uk/biology/research/behaviour/vision/4d.html), but I've just skimmed through it. I might have a proper look and search some more later.

 

[King Edward]

Another one along the same lines is that the bright color makes the BOP less likely to bite its own feet/legs while feeding.

This sounds a plausible possibility, although you'd think a bird would know not to bite off its own feet.

I doubt that having yellow legs/talons makes Sparrowhawks and other raptors significantly more visible to prey. In flight, the legs are tucked well away and are pretty inconspicuous, and by the time they're swinging the talons forward to grab the prey it's a bit late for the latter to be worrying about the colour of its legs.

On a bird perching in a tree, again I doubt the leg colour is going to be that conspicuous to potential prey species, which are going to be much more concerned with keeping a lookout for moving hawk/cat shaped objects, watching their companions and listening for alarm calls etc. than with peering into bushes to look for yellow legs. Especially since these are not a particularly striking feature of hawks in flight, which is where the danger is really coming from.

Unfortunately, I don't have a better suggestion to offer.

 

[fugl]

This sounds a plausible possibility, although you'd think a bird would know not to bite off its own feet..

Well, it's not really a matter of "knowing", but of rendering the feet & legs more conspicuous so as to decrease the likelihood of the hawk accidentally injuring itself during the feeding frenzy.

I doubt that having yellow legs/talons makes Sparrowhawks and other raptors significantly more visible to prey. In flight, the legs are tucked well away and are pretty inconspicuous, and by the time they're swinging the talons forward to grab the prey it's a bit late for the latter to be worrying about the colour of its legs.

On a bird perching in a tree, again I doubt the leg colour is going to be that conspicuous to potential prey species, which are going to be much more concerned with keeping a lookout for moving hawk/cat shaped objects, watching their companions and listening for alarm calls etc. than with peering into bushes to look for yellow legs. Especially since these are not a particularly striking feature of hawks in flight, which is where the danger is really coming from.

I think you're under-estimating the power of natural selection over long periods of time. In the absence of a countervailing benefit of some sort, all that's required for the yellow color of the legs & feet to be actively selected against is for it to make the BOP slightly--even very slightly--more conspicuous to prey or predator than some duller color, & it's hard to imagine that it doesn't at least under some circumstances.

But, obviously, the last word has yet to be said on this question

 

[Firecrest5]

Raptors don't actually "frenzy" feed in my experience,they will vigorously pluck (especially accipiters) before then breaking into the flesh to eat.

They also are not stupid and would not bite their own legs or feet.

I dont know the answer as to why they are coloured yellow, but I really dont think it is to stop them chewing themselves accidently.

Well, it's not really a matter of "knowing", but of rendering the feet & legs more conspicuous so as to decrease the likelihood of the hawk accidentally injuring itself during the feeding frenzy.

 

[fugl]

Raptors don't actually "frenzy" feed in my experience,they will vigorously pluck (especially accipiters) before then breaking into the flesh to eat.

They also are not stupid and would not bite their own legs or feet.

I dont know the answer as to why they are coloured yellow, but I really dont think it is to stop them chewing themselves accidently.

I too have watched accipiters (& other BOPs) pluck & eat their prey on many many occasions.. In my experience (as in yours) they go about it quite vigorously, biting down hard on feathers or flesh, & I can easily imagine them accidentally injuring their legs or feet in the process. But I don't insist on any of this; I was just making a suggestion which I still, however, consider a perfectly plausible one.

Once again, it's not a matter of knowledge or brains but of accidental injury which can happen to anyone, stupid or intelligent. And as I said before, all it would take is a very slight chance of accident for natural selection to come into play.

 

[Firecrest5]

Hi Fugl

I wasnt having a go, just passing comment, apologies if it came across wrongly.

As a falconer of numerous years i have never observed my hawks bite themselves whilst feeding, that was the point I was trying to make. it just doesnt make sense to me. I obviously observe my hawks feeding at very close range, often on my fist.

Rgds
F5

 

[dantheman]

Sexual selection and indication of general health of a bird may also be a factor - do unwell birds go 'off colour' at all?

 

[fugl]

Hi Fugl

I wasnt having a go, just passing comment, apologies if it came across wrongly.

As a falconer of numerous years i have never observed my hawks bite themselves whilst feeding, that was the point I was trying to make. it just doesnt make sense to me. I obviously observe my hawks feeding at very close range, often on my fist.

Absolutely no offense taken, Firecrest, & my apologies if I inadvertently gave that impression.

And, of course, your birds haven't accidentally bit themselves while feeding--their feet & legs are yellow.

 

[Firecrest5]

actually, not particularly bright yellow....maybe I should blunt her beak just to be on the safe side.......

And, of course, your birds haven't accidentally bit themselves while feeding--their feet & legs are yellow.

 

[fugl]

Sexual selection and indication of general health of a bird may also be a factor - do unwell birds go 'off colour' at all?

I'm not quite sure how sexual selection might play out in this case, since (AFAIK) the legs & feet of the 2 sexes are equally yellow (or at least I think so; Firecrest5 will know the truth of this).

Do unwell hawks go off color? Don't know. Firecrest5, what's been your experience?

 

[MJB]

Sexual selection and indication of general health of a bird may also be a factor - do unwell birds go 'off colour' at all?

Leg (and bare-part) colour of many birds is at its most intense during or just before the breeding season that's probably a mate-attractant factor, a demonstration of 'fitness'. Birds that are not at their peak at this time are probably less likely to mate, and so 'unwell' birds are unlikely to reach this peak.

I seem to remember reading some time ago about Grey Partridge loss of productivity being due in part to a significant proportion of males not reaching peak breeding condition because of poor intestinal condition. One theory was that the artificial breeding of Common Pheasants leading to several mass releases every year had allowed their intestinal flora to evolve more rapidly through many more generations than would occur if there was just one reproductive season per year. These flora were excreted in the wild and the poor condition of Grey Partridge was down to their inability to cope with the evolved flora. Doubtless much research since has supported or countered that suggestion.
MJB

 

[fugl]

Leg (and bare-part) colour of many birds is at its most intense during or just before the breeding season that's probably a mate-attractant factor, a demonstration of 'fitness'. Birds that are not at their peak at this time are probably less likely to mate, and so 'unwell' birds are unlikely to reach this peak.

Fair enough, but does any of this apply to birds of prey specifically? It certainly could, since many BOPs have a "dangling legs" component to their displays which bright foot/leg colors might serve to enhance. But whether it actually does apply is another question. I just checked the BNA on-line-accounts for Cooper's & Sharp-shinned hawks & neither says anything on the subject except (in the case of the Sharpie) that "overall, soft parts of females slightly less bright than those of males".

Anyway, interesting stuff.

 

[ChrisKten]

Well, from what I've read, it seems that we have "3D" colour vision, and Birds have "4D" colour vision; so we've no idea what a bird sees. Although the leg and feet colour stands out to me (as I said, it's often the only way I know the Sparrowhawk is in the trees), there's no way of knowing if it's the same for birds. But as Fugl said, the colour would've been selected out if it put the Hawk at a disadvantage.

As for the "peering into bushes to look for yellow legs" mentioned a few posts back, that's often what birds do, well the peering part. When the birds arrive in my garden to feed (feeders are hanging in the trees), the first thing they do is look at the trees. When they feel there's nothing in the trees, they fly into the trees, but they don't feed. They then look up and around the tree, as they can't see what's deep in the tree until they fly into the tree themselves. If they see a suspicious shape (or colour?) they spook and fly back out of the tree and into cover. One other thing, it's often the Corvids that spot a Sparrowhawk hiding in the trees/bushes, the Crows in particular; maybe it's the leg colour that they, like me, notice first.

 

[Firecrest5]

No, unwell hawks leg/feet colour are not generally affected although the only illness I#ve really encountered personally was Redtail with a broken radial bone in her wing!! Raptors are very good at hiding illness unfortunately, so by the time they show signs it is often to late. The eyes are usually the best indicator of illness, if they are not sparkly and clear there is usually something amiss.

Leg colour can differ even amongst siblings as can be seen in this pic of a clutch of peregrines we rung this season.

Do unwell hawks go off color? Don't know. Firecrest5, what's been your experience?