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A graph of the average area of types of habitat in territories of non-cooperative and cooperative breeding families
Average Area of Types of Habitat in Territories of Non-Cooperative and Cooperative Breeding Families Despite the fact that non-cooperative parents outnumbered cooperative parents, the cooperative families controlled more of every kind of habitat, especially ideal foraging areas (edge zone), due to the assistance of their helpers (Adapted from Kesler&Haig 2007).

Adult nuthatches usually resort to helping behavior following personal nest failure (Cox et al. 2007). The main causes of this failure are often depredation by higher consumers or the destruction of their nest by fire or other natural phenomena. The secondary motivation for helping behavior is the inability of young adults to successfully find a mate and breed. This is often attributed to a shortage in the female nuthatch population or an increased density in local nuthatch nesting sites (Cox et al. 2007). Female nuthatches are more susceptible to predators because they are often taking care of young progeny at the nest, while the males collect food. As a result, they succumb to predation by animals looking for nuthatch eggs or chicks. In reference to the availability of territories, an increased density in nesting sites results in a reduced dispersion of resources among individuals. This decreased supply of resources makes it more difficult for breeding pairs to sufficiently provide their nestlings with food; as a result many pairs will either choose to not produce offspring or become helpers at their parents’ nests. Thus, in some bird species the incentives for becoming helpers are solely based on selfish interests, such as securing personal security and food sources, rather than helping indirectly related nestlings survive. In such cases, helping behavior is the cost these individuals pay for access to the benefits of communal living.

Grandparent helpers

So far, only young helpers capable of reproducing have been examined. Older birds that have become too old to have offspring, however, also sometimes take up the role of helper.

A Seychelles Warbler
Seychelles Warbler
A passerine endemic to the Seychelles Islands, they live in cooperatively breeding units containing up to 3 generations of individuals.

A grandparent as a helping subordinate in a cooperative system is a phenomenon that has been observed in a few exclusive species. The Seychelles warbler ( Acrocephalus sechellensis ) is one of these unique species ( [link] ). It is a small song bird found exclusively on the Seychelles islands. Interestingly, the majority of helpers within this species tend to be females (Richardson et al. 2002). Observations gathered over several years suggest that dominant, reproducing females are occasionally displaced by younger, more fertile females (Richardson et al. 2007). These displaced birds either become floaters or choose to join a cooperatively breeding family as a helper.

A population of these Seychelles warblers on Cousin Island in the Indian Ocean has been strictly monitored since 1981. By recording the complete life history and pedigree of the studied warblers Richardson et al. were able to study the phenomenon of grandparent helpers, which make up roughly 10% of the helper population (2002). Between 1981 and 2004 it was observed that about 14% of females in dominant breeding positions lost their status through usurpation by another female, in the remaining cases the females retained their position until they died. 68% of deposed females became subordinates, while the rest became floaters (Richardson et al. 2002). Thus, becoming a helper appears to be a favored outcome among these individuals.

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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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