Typical artificial baits for smaller passerines are shaped like large mealworms and use lard as a base--can add peanut butter, etc. Obviously you cannot make entirely uniform (taste, texture) baits if carbs, protein and fat vary, but you can make them look very similar. For crows (Carrion crows? Hooded crows), a bait like an insect larvae would work. However, if your optimal foraging experiment looks at size vs nutrients, you might try putting a variable quality food inside peanut hulls. American crows like and fairly readily learn to use peanuts. I assume carrion crows would also. thus you could vary the apparent size of the item as well as nutrient content.

Don't place them in piles or too close together, as crows are usually suspicious of new things, and large amounts are more so than a few objects well separated (not hiding anything under or between??? who knows).

I'm currently analyzing footage of corvids and the bait being used is grated cheddar cheese. It seems effective so maybe you could incorporate this with some form of carbohydrate?

Try canned or dry dog food with different levels of carbs, fats, protein etc. Such food fits the crow's omnivorous appetite. Good luck. Dr. Bill

Dear Lawrence,

There was a good study on Starling feeding behaviour (see Anglia Ruskin University's library) by Jessica Folkes in about 1996 - she used giant fat balls (with other food stuffs mixed in to it) on a target area and recorded the different behaviour types exhibited, timings, etc, etc!

You could also try fried chicken strips for protein (fried because they'll be nicer to handle among other reasons).

I'd have to agree with W. Frankllin above that pet food would both be easy to work with in the field and offer variability in carbs, protein, and fat.

If you want to test optimal foraging decisions, it is often necessary to use foods that are strictly comparable in critical ways, such as appearance or size or color. Pet foods offer a lot of scope in fine calibration of protein and fats, especially, (e.g. diff between cat and dog foods, or puppy and adult dog formulations or "cheap" brands and the "all meat" brands) but they may be difficult to work with, when varying one or two things at a time. But--that of course depends on the exact research question.

In using peanut shells as bait, from personal observation, crows won't take peanuts (even with the shells broken in half) if there are local "yummier" nuts like paper shell pecans in abundance. It would pay to know what your study crows like that is in short supply locally.

From long term 12 year personal observation, I do not agree. Different experiences "feeding" crows may speak to local familiarity and "cultural" preferences. Crows here will take bread pieces, dry cat food, as well as peanuts IN THE SHELL which they can cache readily, even if other things are provided.

Anne, I agree-it depends upon what food is "locally" abundant to local family groups. If a high quality protein/fat food, abundant in excess, natural food is preferred-peanuts can be rejected as well as lower fat acorns. I have observed crows near pecan groves look at peanuts in the shell and consistently discard them (if they'll even pick them up)-they won't even cache them-the blue jays will eat them, but they have a more difficult time accessing the pecans. Winter transients will take peanuts, but probably have been habituated to them as well as what pecans are left in the groves over winter are well protected by the residents. Before using a peanut shell or any kind of natural container to protect a manufactured food caution is merited to test if the study area crows even see that shell with the natural food in it as acceptable first before going to all the trouble to alter its contents.

In non pecan areas you'd likely be hard pressed to find an American crow who wouldn't at least investigate a peanut. Pecans are just an example-over abundance of any food source can allow pickiness-it would simply pay to know what the study crows eat and local food abundance.

Northwestern Crows readily took peanuts in shells and even preferred them to various other food options I presented.

In 2008 I performed an experiment with wild birds (mostly passerines) foraging pastry baits made of butter and flour. More details in the published paper: Does colour polymorphism enhance survival of prey populations? Proc. R. Soc. B 2009 276, 2187-2194

Good luck!

I got busy teaching shortly after I posed this question, and did not get around to thanking everyone who contributed--I really do appreciate the thoughtful answers. There are some good ideas to try out here, and though this particular project will be short, I hope to develop this baiting technique further in the future. I hope we can learn something about the local preferences effect; the crows closest to my office feed heavily on mussels which are exposed during low tide in the little fjord outside our building. Others feed regularly on food scraps in town.

Thanks for great comments, Jon. Some things I had thought about but others, not. Yes, one needs to associate a color or something with each treatment (where a treatment can be some aspect of nutritional quality). One can also try to "compete" high quality with quantity or risk or handing time. A reason I would love to work a bit with crows is that they are so intelligent, learn fast, and also will learn to recognize us as individuals and as "good guys", making it possible to move our baiting around a bit if we want to or must.

I am worried a bit about how to keep the gulls away while still encouraging crows.

Ants aren't a problem here, but rain is (rains over 230 days a year on average), so maybe your glass tubes on a slope idea could work.

Your idea about using patterns is intriguing. That is a dimension I hadn't thought about at all, could be really fun to try. Could crows learn that a circle of baits is low quality, while a triangle is high quality, for example??

These are students who will become science teachers. Ultimately, I would simply like to figure out experimental methods which they could easily adapt for high school students. I think that once one can find a good baiting system, this can be great, as it should be very simple for students to quickly come up with their own hypotheses to test.

Lawrence, please report back your students findings!

This is a lovely discussion.

I suggest using mesh tubes of various diameters to hold the food items. Select the holes in the mesh for crow beaks sizes, and mix the food items with inedible substrate (plastic tubes, pebbles) to generate diminishing returns.... Giving Up Densities. The more food items the crows remove the more favourable the food item.