Editing Reciprocal altruism (section)

===Nest protecting===

[[File:Arctic tern (Sterna paradisaea) attacking, Amsterdam island, Svalbard.jpg|thumb|[[Arctic tern]]s protect their offspring extremely aggressively by very quick drop-downs from a stationary flight over their enemies. Other birds often benefit from this behavior by breeding very close to the Arctic terns.]]
[[Red-winged blackbird]] males help defend neighbor's nests. There are many theories as to why males behave this way. One is that males only defend other nests which contain their extra-pair offspring. Extra-pair offspring are juveniles which may contain some of the male bird's DNA. Another is the tit-for-tat strategy of reciprocal altruism. A third theory is, males help only other closely related males. A study done by The Department of Fisheries and Wildlife provided evidence that males used a tit-for-tat strategy. The Department of Fisheries and Wildlife tested many different nests by placing stuffed crows by nests, and then observing behavior of neighboring males. The behaviors they looked for included the number of calls, dives, and strikes. After analyzing the results, there was not significance evidence for kin selection; the presence of extra-pair offspring did not affect the probability of help in nest defense. However, males reduced the amount of defense given to neighbors when neighbor males reduced defense for their nests. This demonstrates a tit-for-tat strategy, where animals help those who previously helped them. This strategy is one type of reciprocal altruism.<ref>{{cite journal |last1=Olendorf |first1=Robert |first2=Thomas |last2=Getty |first3=Kim |last3=Scribner |title=Cooperative Nest Defence in Red–winged Blackbirds: Reciprocal Altruism, Kinship or By–product Mutualism? |journal=Proc. R. Soc. Lond. B |volume=271 |issue=1535 |pages=177–182 |date=22 January 2004 |doi=10.1098/rspb.2003.2586 |jstor=4142499 |pmid=15058395 |pmc=1691571}}</ref>