Mating Monday: Cooperative Breeding

If you missed the previous Mating Monday posts you can check them out here and here.

Cooperative breeding occurs when a mating pair has other birds of the same species helping raise young from one nest. Many time the “helpers-at-the nest” are previous offspring of the parents, but sometimes non-related individuals provide care. This system is widespread throughout the animal kingdom and practiced in approximately 9% of bird species.

“Helpers” play multiple roles. They assist parents with defending the nest and feeding the offspring. A study of Brown-headed Nuthatches (Cusick et al., 2018) found that helpers also removed fecal sacs, but had no part in nest excavation and had no influence on maternal egg production. Cusick et al. concluded that the offspring raised in cooperative groups had more access to food and therefore weighed more. The cooperative nests were also more likely to fledge at least one offspring. Cooperative breeding seems to usually have positive effects for the breeders. But why would an individual forego their opportunity to breed in order to help a nest in which they are not passing on their own genetic material?

There are many factors that influence why cooperative breeding groups exist. One reason may be that environmental constraints limit the opportunities for young birds to breed. Many species that use this system live in regions with low temperature variations and warm winters. This allows the species to become sedentary and establish year-round breeding territories. There may be limited territories due to high-quality habitats being saturated with mature breeders. Low mortality, small clutch sizes, and longevity of offspring contributes to a more stable population that has lower turnover rates, so more birds are available as helpers. Skewed sex-ratios or a shortage of partners (usually females) may also encourage cooperative groups. There are more cooperative breeding groups in altricial species (incapable of moving around on its own shortly after hatching) than precocial (capable of moving on its own shortly after hatching).

Just because cooperative breeding is practiced within a species does not mean that all individuals of the species participate in the system. For example, studies have found that 20-30% of Brown-headed Nuthatches use cooperative breeding as a strategy, with many of the helpers being second-year birds. A study of Long-tailed Tits by Meade & Hatchwell found that helpers had higher overwinter survival rates than non-helpers. Whether or not an individual tit decided to be a helper was determined by the availability of a relative with an active nest. They found that tits that decided to help a relative had a 61% survival rate and the survival rate of those who did not have any relatives with an active nest was 52%. However, male birds that chose not to help a relative with an active nest had a survival rate of 24%. The authors found individuals among the helpers were in good physical condition, the birds without relatives to help were a mix of good/poor condition, and the birds that chose to not help relatives were in poor condition. Meade & Hatchwell also suggested that helping did not have significantly positive effects on reproductive success in the future.

Long-tailed Tit (Image by Alexis Lours via wikimedia commons)

In addition to higher survival rates, helpers may receive other benefits. Helpers may improve their chances of inheriting a mate, territory, or nest. They also gain experience in foraging and may form alliances. Strengthening the genetic makeup of a species through the survival of offspring may be an indirect fitness benefit to the helpers and breeders.

There are many North American bird species that use cooperative breeding. These include Florida Scrub-Jays, Acorn Woodpeckers, Red-cockaded Woodpeckers, Grove-billed Anis, Pygmy Nuthatches, and Gray-breasted Jays.

Brown-headed Nuthatch (Image by DickDaniels via wikimedia commons)

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References

• Arnold, K. E. & Owens, I. P. F. (1999). Cooperative breeding in birds: the role of ecology. Behavioral Ecology, 10(5), 465-471. https://doi.org/10.1093/beheco/10.5.465
• Cusick, J. A., de Villa, M., DuVal, E. H., & Cox, J. A. (2018). How do helpers help? Helper contributions throughout the nesting cycle in the cooperatively breeding brown-headed nuthatch. Behavioral Ecology and Sociobiology, 72(43). https://doi.org/10.1007/s00265-018-2470-1
• DickDaniels. (2013, April 2). Brown-headed Nuthatch [Photograph]. Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Brown-headed_Nuthatch_RWD13b.jpg
• Dreelin, A. (2015). Cooperative Breeding? In My Backyard?. Project Feederwatch. https://feederwatch.org/blog/cooperative-breeding-backyard/
• Ehrlich, P. R., Dobkin, D. S., & Wheye, D. (1988). Cooperative Breeding. Stanford.edu. https://web.stanford.edu/group/stanfordbirds/text/essays/Cooperative_Breeding.html#
• elfruler. (2018). How And Why Birds Cooperatively Breed. elfruler.com. https://www.elfruler.com/?page_id=908
• Lours. A. (2022, January 15). Long-tailed tit Gennevilliers 04 [Photograph]. Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Long-tailed_tit_Gennevilliers_04.jpg
• Meade, J. & Hatchwell, B. J. (2010). No direct fitness benefit of helping in a cooperative breeder despite higher survival of helpers. Behavioral Ecology, 21(6), 1186-1194. https://doi.org/10.1093/beheco/arq137

Red-cockaded Woodpecker Wednesday

Last week we learned about the Nuttall’s Woodpecker, who is endemic (restricted to) to California. This week, we are heading to the opposite coast to learn about the Red-cockaded Woodpecker. The Red-cockaded Woodpecker has been on the Endangered Species List since 1970. Because of this, they are one of the best-studied woodpeckers in North America and are intensely managed.

Red-cockaded Woodpecker (Picoides borealis)

Description:

Red-cockaded Woodpeckers are medium-sized with short, straight bills. They are “zebra-backed” (like the Nuttall’s) and have bright white cheeks with black malar stripes. Males have a small red patch of feathers on the rear of their crown and above their cheeks. This is the “cockade” that this species is named for.(A cockade is a small ornament or ribbon worn on a hat). However, the cockade is almost invisible in the field, making it extremely difficult to distinguish the sexes. Juveniles are duller than adults.

A male with his red “cockade” (Image via alabamabirdingtrails.com)

Range:

All the southeastern United States from Texas to North Carolina. Small populations in Oklahoma, Arkansas, and southeast Virginia. In John James Audubon’s time (mid-1800s) he considered the Red-cockaded abundant from New Jersey southward to Texas, but it’s range has been drastically diminished, about an 86% decrease between 1966 and 2014            (according to the North American Breeding Bird Survey).

Habitat:

Old-growth pine forests, particularly longleaf pine. In order to thrive Red-cockadeds need pine forests that are extensive, living, and maintained by fire to clear undergrowth every 1 to 5 years. Mature trees that have developed red-heart fungus are also important so it’s easier for the woodpeckers to excavate.

Diet:

Mainly arthropods and insects (50% being ants) and some fruits and seeds. They forage by finding insects on tree barks. Females tend to forage on the lower trunk and males on the upper trunk and limbs. Family groups usually forage together.

A female Red-cockaded Woodpecer (Todd Engstrom/CLO via melletteforestry.com)

Breeding/Nesting:

Mating pairs can form throughout the year, but mainly in early spring. Red-cockaded Woodpeckers are monogamous, but sometimes switch their partner between breeding seasons. Courtship displays include “corkscrew” flights will rapid calls and flutter-flights. Like the Acorn Woodpecker, Red-cockaded are cooperative breeders, meaning offspring will stay and help raise the new young after they fledge.

They are the only North American woodpecker to nest almost exclusively in live trees. Females lay between 2-5 eggs and are incubated by the parents and helpers for about 10-11 days. The young fledge between 26-29 days. Even though they can feed themselves, the young are usually fed by the male or helpers for up to 5 months.

Sounds:

Very vocal. A beewr or peew that starts hoarse and gets clearer the more excited the bird gets. A sharp peet!

Conservation:

Before European settlement of North America, it’s estimated that there were between 920,000 and 1.5 million breeding pairs. Populations have declined dramatically due to clear-cutting pine forests and fire suppression. It’s now estimated that there are around 14,068 (according to the U.S. Fish and Wildlife Service). Red-cockaded Woodpeckers are intensely managed. Management strategies include prescribed fires and metal plates in nest cavities to restrict large species from taking over breeding spots, and habitat conservation by both federal and private land owners.

Fun Facts:

• Red-cockaded Woodpeckers are known to be aggressive towards Hairy Woodpeckers, Downy Woodpeckers and Blue Jays.
• Families have multiple nest cavity sites on their territory. The male roosts in the best one that has the most sap flow. This is where the female lays the eggs, and the male incubates them at night.