# How do birds know which fruit or seed are harmful **URL:** \ **Category:** Factual Questions\ **Created:** [October 10, 2017, 1:21pm UTC](https://boards.straightdope.com/t/how-do-birds-know-which-fruit-or-seed-are-harmful/798480 "2017-10-10T13:21:48Z")\ **Posts on this page:** 11\ **Page:** 2
**Author:** ![Ignotus](https://avatars.discourse-cdn.com/v4/letter/i/ecc23a/32.png) [@Ignotus](https://boards.straightdope.com/u/Ignotus)\ **Post date:** [October 13, 2017, 1:05pm UTC](https://boards.straightdope.com/t/how-do-birds-know-which-fruit-or-seed-are-harmful/798480/21 "2017-10-13T13:05:21Z")
> [@Mangetout](#): > > Or 3) become extinct. > > (at least, I think that still counts as selection) Or possibly 4) develop immunity to the poison. (As a matter of fact, [hawfinches](https://en.wikipedia.org/wiki/Hawfinch) can feed on cherry pits and yew seeds, which their beaks are powerful enough to crush, apparently without problems.) ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [October 13, 2017, 2:25pm UTC](https://boards.straightdope.com/t/how-do-birds-know-which-fruit-or-seed-are-harmful/798480/22 "2017-10-13T14:25:55Z")
> [@Ignotus](#): > > Or possibly 4) develop immunity to the poison. That’s actually very common. Any species that can figure out how to detoxify a poison that affects most other species will have no competition for that food source. Many insects (which can adapt very quickly due to short generation times) are specialists on particular plants because they have evolved immunity to that plant’s toxins. ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [October 14, 2017, 10:29pm UTC](https://boards.straightdope.com/t/how-do-birds-know-which-fruit-or-seed-are-harmful/798480/23 "2017-10-14T22:29:27Z")
I had a 1# bag of barley in my cupboard I didn’t want so I mixed it in with the pigeon seed. Every morning I throw out a few cups. Most all of the barley was left behind. This puzzled me, it does eventually get eaten but seems to be last choice. The white peas are first choice. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 14, 2017, 10:42pm UTC](https://boards.straightdope.com/t/how-do-birds-know-which-fruit-or-seed-are-harmful/798480/24 "2017-10-14T22:42:09Z")
I’m surprised that nobody has mentioned that most vertebrates have an instinct that causes them to be repelled by any food they ate shortly before becoming sick. This works even if the sickness wasn’t actually caused by the food. It won’t help, of course, against any poison that always kills with the first dose, but most poisons don’t work that way. ---
**Author:** ![coffeecat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/coffeecat/32/3405_2.png) [@coffeecat](https://boards.straightdope.com/u/coffeecat)\ **Post date:** [October 14, 2017, 11:28pm UTC](https://boards.straightdope.com/t/how-do-birds-know-which-fruit-or-seed-are-harmful/798480/25 "2017-10-14T23:28:55Z")
You’d think that instinct would work better with alcohol and hangovers. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [October 14, 2017, 11:54pm UTC](https://boards.straightdope.com/t/how-do-birds-know-which-fruit-or-seed-are-harmful/798480/26 "2017-10-14T23:54:50Z")
> [@coffeecat](#): > > You’d think that instinct would work better with alcohol and hangovers. You joke, but humans have evolved [a particularly effective version of alcohol dehydrogenase.](http://www.sciencemag.org/news/2014/12/ability-consume-alcohol-may-have-shaped-primate-evolution) It probably originally was an adaptation that permitted ground-dwelling primates to detoxify alcohol in fruit that had fallen to the ground and started to ferment. Our attraction to alcohol is actually a beneficial adaptation to the level found in fermenting fruit. It becomes a problem when we ferment large amounts to consume by itself. ---
**Author:** ![Jeff\_Lichtman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jeff_lichtman/32/1531_2.png) [@Jeff\_Lichtman](https://boards.straightdope.com/u/Jeff_Lichtman)\ **Post date:** [October 15, 2017, 1:16am UTC](https://boards.straightdope.com/t/how-do-birds-know-which-fruit-or-seed-are-harmful/798480/27 "2017-10-15T01:16:02Z")
I think **coffeecat’s** point was that the instinct to avoid things that have made us sick seems not to work with alcohol, at least for some people. As for insects that have adapted to eating toxic plants: monarch butterfly caterpillars eat milkweed, most species of which contain toxins. Not only do the monarchs exploit a food source that others can’t, they absorb and accumulate the toxins in their bodies, making them unattractive to predators. Biologists believe the distinct patterns on the bodies of the caterpillars and the wings of the butterflies are warning coloration. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 15, 2017, 2:23am UTC](https://boards.straightdope.com/t/how-do-birds-know-which-fruit-or-seed-are-harmful/798480/28 "2017-10-15T02:23:55Z")
And speaking of warning coloration, that’s another factor the birds have in their favor. Sure, the bird doesn’t want to eat poisonous plants, but the poisonous plants don’t want birds eating them, either. So they’ve _both_ evolved to ensure that doesn’t happen: The poisonous plants have evolved warning signs, and the birds have evolved to recognize those signs. As for alcohol, I think hangovers come too long after the drinking to trigger the effect. And getting so drunk that you get immediately sick is usually also associated with loss of memory, so even if the lesson is imparted, it doesn’t stick. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [October 15, 2017, 3:51am UTC](https://boards.straightdope.com/t/how-do-birds-know-which-fruit-or-seed-are-harmful/798480/29 "2017-10-15T03:51:00Z")
> [@Jeff\_Lichtman](#): > > I think **coffeecat’s** point was that the instinct to avoid things that have made us sick seems not to work with alcohol, at least for some people. My point was that although alcohol is a poison, we have adapted to it so it doesn’t make us as sick as it does other animals. The fact that we are attracted to it in small amounts is in fact adaptive. It only really makes us sick under artificial modern conditions when we have access to too much of it at one time. ---
**Author:** ![Jeff\_Lichtman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jeff_lichtman/32/1531_2.png) [@Jeff\_Lichtman](https://boards.straightdope.com/u/Jeff_Lichtman)\ **Post date:** [October 15, 2017, 4:51am UTC](https://boards.straightdope.com/t/how-do-birds-know-which-fruit-or-seed-are-harmful/798480/30 "2017-10-15T04:51:41Z")
> [@Chronos](#): > > And speaking of warning coloration, that’s another factor the birds have in their favor. Sure, the bird doesn’t want to eat poisonous plants, but the poisonous plants don’t want birds eating them, either. So they’ve _both_ evolved to ensure that doesn’t happen: The poisonous plants have evolved warning signs, and the birds have evolved to recognize those signs. I’m familiar with warning coloration in insects and some other animals, but not in plants. A brief web search shows a couple of articles about plants using color to warn that they have armaments (spines, thorns or prickles). I can think of a lot of cases, though, where plants use bright colors to attract herbivores. Fruits that are brightly-colored attract birds and other fruit eaters, which spread the plant’s seeds (this is why fruits turn color when they’re ripe). Brightly-colored flowers attract pollinators. Can you name some plants that use warning coloration to deter birds? ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [October 15, 2017, 6:25pm UTC](https://boards.straightdope.com/t/how-do-birds-know-which-fruit-or-seed-are-harmful/798480/31 "2017-10-15T18:25:57Z")
> [@Colibri](#): > > The pits contain cyanide. Most birds pass them through the digestive tract, but if you give them to parrots or other large seed-eating birds they can crush the seeds and release the poison. Ah, I knew that; I just thought that birds passed them untouched. I never thought about about seed eaters. I have always assumed that the prunus fruits evolved edible fruit as a way to get the seeds spread and poisonous seeds evolved in parallel with birds evolving to not chew the seeds. All so birds would be fed and seeds would be spread. [Previous page](https://boards.straightdope.com/t/how-do-birds-know-which-fruit-or-seed-are-harmful/798480.md?page=1)