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Message: <blockquote data-quote="brilsly" data-source="post: 1267920" data-attributes="member: 68493">Hi all, thanks for the many interesting comments over the weekend. To give you a bit more background to this project, it's looking at the interplay between emotions and cognition. For example, it's been shown in humans that your anxiety state differentially affects your interpretations. One experiment used speaking words like "dye/die" aloud, they found that people with higher anxiety levels will tend to write the more negative word (die) down when asked to interpret what was said. We've started to try to replicate this sort of thing in birds. We started off by showing them eyespots and playing them alarm calls etc. to see if scaring them with alarm calls made them more scared of eyespots. However, we had no joy, mainly because it seems that the birds don't think eyespots look like eyespots (i.e. they don't think "that might be a cat"), they just seem to think that bright contrasting things are less likely to be palatable food. Anyway, so one of our stimuli in the experiment was a sparrowhawk calling (a male when presenting food to the female). To cut a long story short, they couldn't give a toss about hearing sparrowhawks. In mammals you can use scents to imply that predators might be around but for the starlings, it looks like it's only visual stimuli that will work, hence this work on the silhouettes flying overhead. The theory is that there are costs associated with fleeing due to false alarms (lost feeding time, energy etc.). So you should have some threshold above which you say "that's a sparrowhawk, I'm out of here". This threshold should change depending on how vulnerable you are (i.e. weak or ill birds) and therefore with some measure of this vulnerability (which could, if you have a pinch of salt handy, be called anxiety). Therefore, if we have more anxious birds then they should more readily flush up. We have already shown that bathing in these birds affects flight performance (they hit more obstacles in an obstacle course when they haven't had a bath). I'm in the process of showing that when they haven't bathed they're more risk averse (they're slower to unfreeze after hearing an alarm call with no predator obviously present). Now it'd be neat to show that if they haven't bathed, they're in a worse condition and therefore more likely to see sparrowhawks in ambiguous silhouettes. You'd certainly expect birds to flush to all sorts of silhouettes if they're out feeding somewhere where they're feeling very vulnerable (i.e. out on a feeder in the open).Jan, that's a very interesting comment you made. I've certainly seen lots of evidence that birds can distinguish amongst different threats (cuckoos vs. hawks in warblers, differential responses of waders to different raptor species etc.). I think it's very likely that there's a significant degree of similarilty due to flight constraints, but if they could look more similar (to disguise appearance) then you'd certainly expect evolution to favour that. One thing I've never heard but might be possible is that they change their flapping style in flight approach. There are certainly butterfly species where tasty species mimic not only the colour but also the flight pattern of poisonous butterflies. I wonder whether it'd pay for a hobby to try flapping like a swift when it's up very high and making an attack approaches? Just a completely random thought....probably very wrong.Anyway, so finally, I think I may have found quite a convincing sparrowhawk photo for that silhouette (for anyone who recognises these photos, I'd like to say that these will never be used for commercial purposes). The one thing now I'm thinking is I really bloody hope that it's a female, since from what I understand males are not quite such a big threat to starlings. Is this one a quite obviously recognisable sparrowhawk though?Thanks to everyone who's commented again.Ben</blockquote>

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