Researchers Suárez-Rodríguez et al., observed house finches (C. mexicanus) and sparrows (P. domesticus) on the National University of Mexico campus in Mexico City routinely pulling apart cigarette butts to obtain the filters. The birds were found to incorporate the filters in their nests leaving researchers to speculate the purpose of used cigarette butts. Using heating elements to attract parasites, they found that probes covered in "used", i.e. artificially smoked, cigarette butts attracted fewer ectoparasites than those that were not used. These observations suggest that the birds may be using discarded cigarette butts, which collect chemicals like nicotine, for pest control in their nests. Direct examination of the nests post-breeding supported these findings by showing that nests with more butts had fewer parasites.
Since eggs are rather porous, the potential health risks for cigarette butt-insulation on developing embryos or adult birds are currently unknown.
Suárez-Rodríguez M, López-Rull I, and Macías Garcia C. Incorporation of cigarette butts into nests reduces nest ectoparasite load in urban birds: new ingredients for an old recipe? Biol letters.9(1), 2013. doi: 10.1098/rsbl.2012.0931
Ahh, the awesome splendor of nature! Toolmaking ability in birds!
The house finches found an object in their environment and modified it to produce an instrumental use or benefit that was not immediately apparent from the visible characteristics of the object or its modification.
Here's the test for this:
Take a quantity of un-smoked cigarettes, cut loose the filters, so you now have fresh unused filters.
Take an equivalent quantity of used cigarette butts and cut loose the filters in the same manner. For this part we will want to recruit smokers who will leave their filters intact rather than crushed in the manner in which cigarettes are usually extinguished, the point being that the used filters should have as close as possible to the same appearance as the unused filters.
Now you have a quantity of used filters, and un-used filters, that can be spread in an area occupied by the birds. Let's say you start with fifty of each, total of 100 filters.
All of the filters would be numerically labeled from 001 through 100 using fine marking pens. Filters 001 - 050 would be unused, filters 051 - 100 would be used. The filters would be scattered at random into an area with marked boundaries. The area would be marked off with police tape and traffic cones bearing notes asking people to not walk into or throw any more cigarette butts into that area.
The test would be started at sunrise and continue until sunset, with a human observer watching at all times. At sunset the remaining filters would be picked up and counted into a "fresh" and "used" pile, to ascertain how many of each type was taken away by birds.
Hypothesis: birds will preferentially take away the used filters rather than the fresh filters, thus there should be statistically significantly more fresh filters than used ones remaining at the end of the test.
Inference: Birds are using their sense of smell to detect which butts are used ones. Further inference: they are aware that something in the used filters is repelling parasites. This would count as an "instrumental" use of the butts, in other words, toolmaking in birds.
Counter-hypothesis: They are only using the butts as a source of fluffy stuffing for their nests, for insulation or similar properties. In this case we would expect to find no significant difference between the quantity of fresh and used filters taken from the test area at the end of the day.
OK folks, there's a bit of backyard science you can do, that only entails having your friends who smoke save their filters for a couple of days, and then buying a few packs of cigs to remove the fresh filters (give your smoking friends the newly-unfiltered cigarettes to smoke), and then planning a day when you and a friend can go bird-watch for the whole day.
Know what's really cool?
Every time we come up with some smug generalization about what makes humans "different" to "animals" (should be "other animals" but I quibble!;-), and "more special," nature throws us a curve ball and shows us other animals who have the same behaviors.
Language? Great apes can be taught to use signs and symbols at about the proficiency level of a 4-6 year old human. There are also indications of language-type communications among marine mammals and among elephants.
Tool-making? More great apes, and also, very interestingly, crows.
Free will? Voluntary turning-in-flight behavior of fruit flies (Maye et. al., "Order in spontaneous behavior, PLoS One, 16 May 2007).
So now we may be looking at toolmaking in smaller birds with brains that are arguably less complex than those of crows.
I just freakin' love it when we keep finding examples of how all these "special" characteristics of humans are part of nature at-large. For the religiously-inclined, if we have souls, so do other critters.
And now I'll tell you why humans persist in claiming that we are "special" and other animals "don't have souls" or are "not like us."
>>> It gives us an excuse to eat them without violating the cannibalism taboo. <<<
Think about that for a while and you'll see that it's true.
There's "food," there's "not-food," there's "dirt" (a category of "not-food" that evokes revulsion), and there's "people" (another category of "not-food" for which the thought of eating it evokes revulsion). For example spaghetti, paper, dog doo, and your cousin. Paper is "not-food" but eating a little of it won't make you sick, and the thought of doing so doesn't make you nauseous. The thought of eating dog doo is revolting. The thought of eating your cousin is revolting in a different way. And the thought of eating your cousin's dog is revolting in a similar way, because in our culture, "dog" is "people."
Though in Southeast Asia, "dog" is very often "livestock" therefore OK as "food."
On the other hand in India where the Hindu belief in reincarnation crosses species lines, the thought of eating cow is revolting, because "cow" is "people", such as your reincarnated great uncle.
Now generalize those examples, and you see why we like to pretend that animals "aren't like us."
But the more we look, the more we realize that animals are very much like us. And I say that as an omnivore who has to grapple with the ethics of this and has no firm conclusions.
I think, this is a good idea. But if you have that smoking habit, you can still see for the most safe one for smoking.