Cooperative breeding in birds

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.

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] ).

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.