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Furthermore, helpers are also eligible to inherit their parents’ territory once the parents die. Consequently, any lost reproductive chances they endure while waiting to inherit the territory is offset by the long-term fitness gains of eventually controlling the territory. In an environment with a limited number of ideal territories, such as the Micronesian islands, it is well worth a young kingfisher’s time and effort to be a helper in order to attain a premier nesting site (Kesler&Haig 2007). Helpers therefore also benefit from a cooperative breeding arrangement by being provided a breeding territory they do not have to fight or search for.

Mechanism of kin recognition in long-tailed tits

Long-tailed tits respond differently to various broadcast calls (Hatchwell et al. 2001). They are able to differentiate between those of kin and non-kin. This discriminatory behavior could be used in deciding which individuals helper tits will commit to helping. The nature of the calls, however, does not always describe the genetic relatedness of the birds, but rather association with a particular group. This observation is further supported by the fact that parents raising foster chicks do not discriminate between them and their direct progeny because all of the nestlings learn to elicit the same vocal cues (Hatchwell et al. 2001). In addition, the helping behavior of cross-fostered siblings shows that they do not differentiate between related and unrelated brood mates, supporting the proposition that the kin recognition mechanism is not innate, but learned through association. Thus, in the case of long-tailed tits, kin selection is based on social relationships rather than actual genetic similarity.

Cooperative breeding thus has many attractive survival benefits to allure prospective helpers. These physical benefits, however, are not the only evolutionary motivation for helpers to assist parents in raising offspring. If the helpers are related to the offspring they are helping to rear, they are actually indirectly benefitting themselves in a genetic sense. By increasing the chance that one of their younger siblings, for example, will survive, helpers are indirectly improving the chance that their own genes will be passed on, since siblings share half of their genes.

Selfish helping

The motivations, however, for becoming a helper in a cooperative breeding system are not always ultimately based upon improving the chance an individual will pass on their genes. Sometimes, adult birds become helpers for the sole reason of accruing personal benefits. This discrepancy has been observed among Brown-headed nuthatches ( Sitta pusilla ) ( [link] ).

Brown-Headed Nuthatch
Brown-Headed Nuthatch
Nuthatches are small cavity-dwelling passerines (perching song birds). They are usually monogamous, pairing with their partners for life.

In a population of nuthatches studied in north Florida, about 20% of adults were recorded to engage in cooperative breeding, indicating it is a relatively widespread phenomenon (Cox et al. 2007). Surprisingly, a survey of nestling survival rates revealed that the presence of helpers did not actually increase nest productivity. Some nests had up to 5 helpers and yet the average number of nestlings raised by cooperatively breeding and single-pair breeding families was both approximately 4 chicks per season (Cox et al. 2007). This statistic indicates that the majority of benefits resulting in helper activity are enjoyed by the native parents, instead of the offspring; all of the nuthatch nestlings, whether they are raised in a cooperatively breeding unit or not, receive the same amount of total care from their guardians. Additional helpers share in meeting this set quota of care, alleviating the responsibilities of other adults while not ultimately increasing the net care delivered to progeny.

Questions & Answers

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Source:  OpenStax, Mockingbird tales: readings in animal behavior. OpenStax CNX. Jan 12, 2011 Download for free at http://cnx.org/content/col11211/1.5
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