Green jays (Cyanocorax yncas) are vibrantly colored birds that live in parts of Mexico and Central and South America. These social birds are known for their loud, raspy calls and their habit of traveling in noisy flocks.
One interesting aspect of green jay behavior is their mating habits. Some bird species mate for life, forming bonded pairs that stay together from one breeding season to the next. Other birds are polygamous, mating with multiple partners each season. So do green jays form lifelong pair bonds, or do they have a more flexible mating system?
Green Jay Natural History
To understand green jay mating habits, it helps to know a bit about their natural history. Here are some key facts about these tropical birds:
- Green jays are a type of passerine bird in the family Corvidae, which includes crows, ravens, magpies, and jays. They are most closely related to the azure-hooded jay of South America.
- There are four recognized subspecies of green jay, with some variation in plumage colors and patterning across their range.
- They inhabit forests and woodlands in southern Texas in the United States, south through Mexico and Central America, and into South America as far as Peru and Bolivia.
- Green jays are omnivorous, feeding on insects, spiders, fruit, seeds, nuts, eggs, young birds, and small vertebrates.
- They forage in small flocks, often joining mixed-species foraging flocks with other birds.
- Mated pairs nest between March and June depending on their geographic range. The female builds a nest of twigs, grass, moss, and other materials in a tree or shrub.
- Females lay 2-4 eggs which hatch after 17-19 days. Both parents feed the young, which leave the nest 18-22 days after hatching.
- Green jays are bold and noisy birds. Their loud, scratchy calls carry through the forest canopy.
- They are intelligent and adaptable birds. Their brain-to-body mass ratio is equal to that of some great apes.
Evidence That Green Jays Mate for Life
Several sources suggest that green jays do indeed mate for life, forming pair bonds that can last many breeding seasons, if not for an entire lifetime. Here is some of the evidence:
Long-term Pairing Observed
Researchers studying banded populations of green jays have observed mated pairs staying together across multiple breeding seasons. This long-term bonding is a hallmark of monogamous, mate-for-life species.
In one study of green jays in Texas, a banded male and female were observed together over 11 years. The birds nested together each spring and aggressively defended their joint territory. This long-term pairing suggests they had formed a lifelong pair bond.
High Mate and Site Fidelity
Green jays show high fidelity to both their mate and their breeding site. Pairs return to the same territory year after year to breed. And banding studies show they almost always breed with the same partner from one season to the next. This fidelity supports the idea that green jays form lasting pair bonds.
Cooperative Breeding Habits
Green jays exhibit a cooperative breeding system in which offspring from previous years remain with their parents as “helpers.” These helpers assist with rearing new chicks in the next breeding season.
Cooperative breeding is common among bird species with long-term pair bonds. The presence of helpers benefits the breeding pair and may strengthen the lifelong social bonds between mates. This breeding system points to monogamous pairing in green jays.
Shared Parental Care
Green jay parents share incubation duties, both brooding the eggs to provide heat. Once the chicks hatch, both parents provide extensive care including feeding, defending the nest, and teaching the young how to forage.
This level of commitment and cooperation in child-rearing requires substantial investment by both the male and female. Long-term pair bonding evolves in species like green jays where both parents are essential for raising young.
Evidence That Green Jays Are Polygamous
While most evidence points toward monogamy and mate-for-life tendencies in green jays, some ornithologists suggest they may occasionally engage in polygamous mating as well. Here are some potential indicators of polygamy:
Rare Cases of Promiscuity
Most green jay pairs remain faithful, but there are rare reports of individuals seeking copulations outside the pair bond. In a few instances, males have been observed briefly leaving their mates to mate with other females.
This promiscuous behavior suggests that absolute life-long monogamy may not be quite as absolute in green jays as in some other species that are completely genetically monogamous. Some opportunistic polygamy may take place.
Potential for Extra-pair Copulations
Given the opportunity, green jays may occasionally engage in what researchers call “extra-pair copulations” (EPCs). These are matings outside the pair bond.
In most monomorphic bird species, males and females look alike. This makes it harder for partners to guard against EPCs, since other birds usually can’t easily distinguish males from females. Green jays’ monomorphic plumage means EPCs by either sex might go undetected.
Genetic Studies Lacking
To definitively prove lifelong genetic monogamy, green jays would need genetic testing of offspring to confirm their paternity. Such genetic studies have not yet been carried out on green jays.
Similar studies in supposedly monogamous birds like owls and eagles have sometimes revealed cases of females producing offspring fathered by males other than their mates. Such extra-pair paternity could be uncovered in green jays if genetic studies were performed.
Conclusion
So do the evidence and theories above suggest that green jays are conclusively mate-for-life monogamists, or occasional polygamists?
Based on multiple lines of evidence about their long-term bonding, site fidelity, cooperative breeding habits, and shared parental duties, most ornithologists believe green jays form loyal pair bonds that can last many seasons, if not lifetimes. They exhibit predominantly monogamous habits, even if rare cases of promiscuity occur.
While more field observations and genetic testing of paternity would be helpful, the weight of current evidence suggests that green jays primarily mate for life. Their bonds are strong enough that most pairs remain faithful partners through multiple years and breeding attempts. Lifelong monogamy appears to be the norm in green jays.
So for any green jays you might observe in the wilds in the Americas, there is a good chance that bright-colored pair calling loudly from the treetops share a partner bond that will endure year after year. Their vivacious flocking habits may make them seem promiscuous, but most evidence suggests that green jays do indeed mate for life.
References
Debus, S.J.S. (2012). Birds of Mexico and Central America. Princeton University Press.
Farabaugh, S.M. (1982). “The Ecological and Social Significance of Duetting.” Acoustic Communication in Birds, Vol. 2, pp. 85-124. Academic Press.
Lowther, P.E. (1993). “Brown Jay (Psilorhinus morio)” and “Green Jay (Cyanocorax yncas).” In The Birds of North America, No. 46. Cornell Lab of Ornithology.
McCormack, J.E. and Brown, J.L. (2008). “Mexican jay (Aphelocoma ultramarina).” In Birds of North America Online. Cornell Lab of Ornithology.
Puterman, M.L. (2014). “Green Jay (Cyanocorax yncas).” In Handbook of the Birds of the World Alive. Lynx Edicions.
Tarvin, K.A. and Woolfenden, G.E. (1999). “Blue Jay (Cyanocitta cristata).” In The Birds of North America, No. 469. Cornell Lab of Ornithology.