Editing Reciprocal altruism (section)

===Warning calls in birds===
[[File:2012-06-09 16-04-22 Switzerland Kanton Graubünden Sagliaz cropped.JPG|thumb|Eurasian jay, ''[[Garrulus glandarius]]'', gives loud alarm calls from its tree perch when it sees a predator.]]
{{further|Signalling theory}}

Warning calls, although exposing a bird and putting it in danger, are frequently given by birds. An explanation in terms of altruistic behaviors given by Trivers:<ref name="trivers"/>

It has been shown that predators learn specific localities and specialize individually on prey types and hunting techniques.<ref name="Murie">{{cite book |first=Adolph |last=Murie |title=Fauna of the National Parks of the United States: Fauna series |url=https://books.google.com/books?id=HO_aAAAAMAAJ |year=1944 |publisher=U.S. Government Printing Office |series=Fauna of National Parks of the United States |volume=Faunal Series No. 5}}</ref><ref name="Southern">{{cite journal | last1 = Southern | first1 = H. N. | year = 1954 | title = Tawny owls and their prey | journal = Ibis | volume = 96 | issue = 3| pages = 384–410 |doi=10.1111/j.1474-919X.1954.tb02332.x}}</ref><ref name="Tinbergen">{{cite journal | last1 = Tinbergen | first1 = N. | year = 1968 | title = On war and peace in animals and man | journal = Science | volume = 160 | issue = 3835| pages = 1411–8 | doi = 10.1126/science.160.3835.1411 | pmid = 5690147 |bibcode = 1968Sci...160.1411T }}</ref><ref name="Owen">{{cite journal | last1 = Owen | first1 = D. F. | year = 1963 | title = Similar polymorphismas in an insect and a land snail | journal = Nature | volume = 198 | issue = 4876| pages = 201–3 | doi = 10.1038/198201b0 |bibcode = 1963Natur.198..201O | s2cid = 4262191 }}</ref>
It is therefore disadvantageous for a bird to have a predator eat a conspecific, because the experienced predator may then be more likely to eat them. Alarming another bird by giving a warning call tends to prevent predators from specializing on the caller's species and locality. In this way, birds in areas in which warning calls are given will be at a selective advantage relative to birds in areas free from warning calls.

Nevertheless, this presentation lacks important elements of reciprocity. It is very hard to detect and ostracize cheaters. There is no evidence that a bird refrains from giving calls when another bird is not reciprocating, nor evidence that individuals interact repeatedly. Given the aforementioned characteristics of bird calling, a continuous bird emigration and immigration environment (true of many avian species) is most likely to be partial to cheaters, since selection against the [[Gene-centered view of evolution|selfish gene]]<ref name=Dawkins06 /> is unlikely.<ref name="trivers" />

Another explanation for warning calls is that these are not warning calls at all:
A bird, once it has detected a bird of prey, calls to signal to the bird of prey that it was detected, and that there is no use trying to attack the calling bird. Two facts support this hypothesis:

* The call frequencies match the hearing range of the predator bird.
* Calling birds are less attacked—predator birds attack calling birds less frequently than other birds.