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Do parents benefit from helpers?

In some species, such as the Long-tailed tit and the Arabian babbler, an inverse relationship between the number of helpers and the provisioning rate of the native parents has been documented. This reduction in care by parents of cooperatively breeding units is often correlated with populations exhibiting low rates of nestling starvation and the possibility of having more than one brood per season (Hatchwell et al. 2000). This observation, for example, has not been recorded in Azure-winged Magpie parents, which do not reduce their chick feeding levels when they are aided (Canário et al. 2004). This is due to the fact that these Magpies produce only one brood every season. As a result, the pressure to successfully raise offspring is much higher than in species that have multiple broods per season. Thus, the parents pass on a more significant share of the benefit helpers contribute directly to their offspring.

Azure-Winged Magpies
Azure-Winged Magpies
These crow-like communal birds can only be found in the Iberian Peninsula or East Asia.

Though this study demonstrates that cooperative breeding can be caused by ecological factors such as weather and the availability of food, it does not describe why a bird chooses to become a helper rather than a floater, a bird with no territorial or rearing commitments. The natural evolutionary preference towards being a helper can be explained by taking a closer look at cooperative breeding in the Micronesian kingfisher.

The benefits of helping

The Micronesian kingfisher ( Todiramphus cinnamominus ) is an endangered native of the Micronesian islands of Guam, Pohnpei, and Palau ( [link] ). These small colorful birds live in forest thickets. Both males and females play a major role in caring for young, and offspring often remain with their parents as helpers after they have reached adulthood. This tendency towards cooperative breeding is of particular concern because kingfishers that decide to become helpers at the nest essentially remove themselves from the eligible reproducing population for that breeding season, forfeiting a chance to pass on their genes. Studies using radiotelemetry and remote sensing to record habitat preferences have revealed, however, that despite this disadvantage, Micronesian kingfishers in cooperative breeding families are able to collectively secure better resources and larger territories than those in single pair breeding families (Kesler&Haig 2007).

A yellow Guam Micronesian Kingfisher.
Guam Micronesian Kingfisher
This subspecies is extinct in the wild as a result of the introduction of brown tree snakes to its native island of Guam during WWII.

The presence of additional mature kingfishers in cooperative breeding units allows them to out-compete single breeding pairs for the most beneficial settling sites ( [link] ). This prospect of access to ideal territories is just one of the evolutionary motivations for birds to participate in cooperative breeding, and may explain helping behavior beyond a kin selection model.

Kesler and Haig’s study also showed that not only did all of the adults in cooperative breeding families enjoy more resources than their single-pair counterparts, all adult members of the cooperative units used equal amounts of resources (2007). Thus, helpers are entitled to the same amount of food and shelter as the native parents, indicating they do not sacrifice their physical well-being to any measurable degree, by participating in a cooperative breeding arrangement. Instead, they are actually given access to exceptional resources they would have not been able to acquire otherwise.

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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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