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

Mating Monday: Are Most Birds Actually Monogamous?

One of my favorite sights of spring is seeing bird pairs around my yard. Throughout April the cute American Robin pair would take evening walks across the lawn looking for food. The Northern Cardinal pair frequents the feeders together and I even saw the male feed the female some seeds. It’s a common sight to see pair-bonded birds in the spring because many bird species are considered monogamous. In his 1968 book Ecological Adaptations for Breeding in Birds, British ornithologist David Lambert Lack estimated more than 90% of bird species are monogamous.

Black-crowned Night-Herons are presumed to be socially monogamous (Image by David Horowitz)

Merriam-Webster defines monogamy in zoology as “the condition or practice of having a single mate during a period of time”. In 2002, a study by Griffith, Owens, and Thurman found that “extra-pair offspring” occurs in 90% of bird species. If 90% of species are monogamous, how can 90% also have offspring sired by another male who is not in the pair-bond?

Well, it turns out monogamy in birds is a little more complex than a Merriam-Webster dictionary definition. From an evolutionary standpoint, the idea of monogamy occurring in animals at all is a bit of a strange idea. If an individual has the opportunity to mate with multiple partners and doing so can increase their fitness (aka: their reproductive success), then why would they choose monogamy? Biologists are learning that when it comes to animals, three types of monogamy come into play: social, sexual, and genetic. Lack’s assertion that 90% of species are monogamous refers to social monogamy. This means that bird pairs work together to raise offspring, but there is no guarantee that they are sexually or genetically monogamous. In fact, the Griffith et al. (2002) study contributes to the idea that genetic monogamy (that the two partners only have offspring with one another) is quite rare in birds. True genetic monogamy does occur in some species, such as Common Loons, Dovekies, Florida Scrub-Jays, and some populations of Red Crossbills. However, at least some females in about 90% of bird species will mate with a male who is outside of her pair bond, a behavior called extra-pair copulation.

Why would a female seek out a mate outside of her social bond? First, her social mate may have genes that are inferior, so mating with a more desirable male can allow a female to pass on better genes to her offspring. Secondly, a female is more likely to get her eggs, which are a limited resource, fertilized just in case her social mate is infertile or incompatible. Lastly, extra-pair copulation allows a female to have genetically diverse offspring by multiple fathers. It’s the “don’t put all your eggs in one basket” idea.

Some Mourning Doves stay together for one breeding season and others may mate for life (Image by Michelle Horowitz)

So yes, a vast majority of bird species are monogamous, but it’s not as clear cut as it seems. Many of our cute little bird pairs have something going on “on the side”. Many birds will only stay together for once breeding season and find a new mate the next. There are some species that do mate for life, but that’s not as common as we once thought.

Infidelity, divorce, and even same-sex pair bonds (although rare) occur in birds. And what about the other 10% of birds that don’t practice monogamy? What mating system do they use? Over the next few weeks we’ll explore some of these interesting avian behaviors on Mating Monday. Stay tuned!

Old Friends

At the end of March, Dave and I visited Cape May Point State Park and South Cape May Meadows for some early spring birding. There were still a lot of winter visitors around, but many spring migrants were starting to arrive.

First of season (year) species during this trip included Ospreys, Field Sparrows, Common Grackles, Greater Yellowlegs, Great Egrets, Eastern Phoebes, Tree Swallows, and my favorite: the American Oystercatchers.

The beach of South Cape May Meadows is where we ran into one of our old friends: Oystercatcher 38. We met 38 last year at the same location, but according to his account from the American Oystercatcher Working Group, 38 is about 8 years old.

American Oystercatcher 38 (Image by BirdNation)

This year 38 was with an unbanded Oystercatcher that could potentially be its mate. They were running around the beach together.

38 with its potential mate (Image by BirdNation)

At one point, 38, his mate, and another pair engaged in a courtship display. During a courtship display, pairs will stretch their necks forward and down with their back parallel to the ground. They will run side-by-side with their mate will making pip! notes and bobbing their heads. Occasionally the pair will fly up in the air while piping. Many times pairs from other territories will join in on the display. When multiple pairs display together it is referred to as a “Piping Tournament” or “Piping Ceremony”. It was fun to see our friend 38 again. Below is a video of their piping tournament.

American Oystercatcher Piping Tournament (Video by BirdNation)

If you ever see a banded oystercatcher I would recommend submitting your sightings to the American Oystercatcher Working Group. They are a great organization, and their website contains a wealth of information about the American Oystercatcher’s life history, behavior, and banding. Check out their website at http://amoywg.org/

Timberdoodle!

Spring is almost here, and we are certainly getting signs of the coming season in New Jersey. The weather is finally starting to warm up a bit, and I’ve been hearing American Robins start their bouncy spring songs each morning. The spring migrants are returning, and that includes a very fascinating and unique species…the Timberdoole!

Well, the Timberdoodle is its nickname (and an awfully cute one at that). I’m referring to the American Woodcock, a small bulbous shorebird that migrates through New Jersey in March.

I heard about these birds pretty early into my life as a birder, but never have had the chance to see them because…I would forget. I would be so busy in the spring that I would remember about the timberdoodle after it already passed through the area. I knew this year would be different.

Dave and I went to Rancocas Nature Center (where I’m a teacher naturalist on some weekends) to watch the display. The meadow at RNC is a great place to check out the Timberdoodle. The Timberdoodle is not just a bird you simply go to just get a sight of, the allure of this little bird is the famous “Sky Dance”.

American Woodcock (Image via Pinterest)

Timberdoodles like to spend their time in brushy fields near deciduous forests. In the cover of darkness, the male Timberdoole will give a distinct buzzy “peent!” to get the female’s attention. After a few calls, the male rockets up into the air with a flutter, soaring up and circling about 200-300 feet in the air. As the male ascends into his dazzling display you can hear his wings twitter. After reaching his peak, the male circles back down to the ground and land in the same spot next to the female. These aerial display can last into the night and take place around dawn as well. Once a pair does mate, the male provides no parental care. Males usually mate with multiple females. The female will feed the chicks for a week, and about a month later the chicks will become independent.

It was really amazing to see the American Woodcock’s sky dance. We observed at least 4 birds participating in the display. We even had a pair fly right over us! I’m so glad we had a chance to observe these magnificent birds in action.

I was able to get a short recording of the “peents” at the beginning of the display (I was too mesmerized watching to record anything after it start lol). You can hear a few peents through the wall of sound that is a bunch Spring Peeper frogs calling.

American Woodcock “peents!” with Spring Peeper background

Have you seen a Timberdoodle? Tell me about your experience in the comments!