Mexican Blue Jay, Cave Creek Canyon Ranch, Cave Creek Canyon, AZ,
January 17, 2021, WJ Beaver
One morning at Cave Creek Ranch, watching the various birds cavort around the bird feeders, we noticed that all of a sudden the little birds were gone and three large Mexican Blue Jays had landed in the trees. They stayed for a bit then moved on and everything went back to normal. Later, when we were walking through the South Fork of the canyon we heard the jays calling as they were disturbed by something in the forest. Called mobbing behavior (4), they band together to intimidate and drive a predator from their territory.
Species Range in Mexico (1) Sky Islands and Madrean Highlands (2)
Mexican Jays have a range that follows a U-shape from SE Arizona south through the Sierra Madre Occidental, east across the mountains of the Transvolcanic belt, and then north through the Sierra Madre Oriental to their only eastern US location in the Chisos Mts. (7)at Big Bend National Park in Texas. Currently, they are typed as 7 subspecies but current genetic and phenotype studies suggest that they may be as many as 4 cryptic species. This method of molecular genetics gives time frames for occurrences but they can be very inaccurate as most genetic timings are way older than any fossil data. Basically, the initial speciation of Mexican Jays goes back at least to the creation of the mountains they inhabit, some 40 to 50 million years ago. It is hard to get your mind around this number. (1) The northern half of the range of the subspecies arizonae is located in a region known as the Madrean Highlands in Mexico and the Sky Islands in Arizona. The Sky Islands are high ranges that are separated from each other by low stretches of desert. Thus they are isolated and contain many endemic species, species found only on certain mountains. West to east through this region the Sonoran desert blends into the Chihuahuan desert. Mexican Jays have been studied in Madera Canyon (3) in the Santa Rita Mts. south of Tucson and continuously since 1969 at the Southwest Research Station run by the American Museum of Natural History in upper Cave Creek Canyon in the Chiricahua Mts. (5)
Mexican Jays have no visible sexual dimorphism and juveniles differ from adults by lighter coloring on their beaks while adults' beaks are generally all black. Juveniles take three years to reach breeding maturity and adults are long-aged some 15+ years. Like Acorn Woodpeckers (11), Mexican Jays are associated with oak trees. While Acorn Woodpeckers store acorns in holes they drill in dead trees called granaries, Mexican Jays cache acorns in the ground. Mexican Jays also eat insects, eggs of other birds, small birds, lizards and snakes, and even bats. (6) Mexican Jays form related family groups of several nests with a simple (linear) dominance pattern based on sex (male) and age. (10) Again, like Acorn Woodpeckers, Mexican Jays are cooperative breeders, meaning that there are related helpers at the nest. The birds practice both polyandry, where females have multiple male partners, and polygynandry, where groups of males and females breed together. Also, from what I can piece together, monogamous pairings only occur by season, not for life.
Monogamy in birds is around 90%. Cooperative breeding can be said to start with a male breeding helper and then extends to sibling helpers. When genetic testing came to bird science in the 1990s it was discovered that there are two types of monogamy, true monogamy and social monogamy in which the male raises eggs from other fathers. There are several theories about why this happens. One is that fitter males and better fathers are not always the same thing so the female goes for the best of both. Another is that this is an incest taboo strategy to protect against mates that are a little bit too related. A study in 2004 (8) has found that Mexican Jays not only have a high degree of the interrelationship among breeding pairs but 60% of females’ fledglings do not belong to the helping father. They also have a very low dispersal rate so no matter where they go they are going to be around relatives. (9)
During glacial maximums, the desert regions between the Sky Islands shrunk and were replaced by forests and woodlands. At other times these lowlands were deserts that isolated the mountains. Breeding behavior in birds reflects the environment they must survive in. Some birds are plastic in their behavior with a repertoire depending on the situation. Others may be less plastic. Acorn Woodpeckers have a larger range than Mexican Blue Jays, extending south to Columbia, west, and north through California and Oregon and east into New Mexico with a seemingly wider set of behaviors. (12) However, they have not had the extensive biogeographic study that was done on Mexican Blue Jays where the flocks in the Chisos Mts. have not only behavioral but slight phenotype differences and are also the most genetically different. (1)
McCormack, J. E., A. T. Peterson, E. Bonaccorso, and T. B. Smith. “Speciation in the Highlands of Mexico: Genetic and Phenotypic Divergence in the Mexican Jay (Aphelocoma Ultramarina): Deep Divergence in a Mexican Highlands Bird.” Molecular Ecology 17, no. 10 (May 2008): 2505–21. https://doi.org/10.1111/j.1365-294X.2008.03776.x.
Data Basin. “Transboundary Land Cover Dataset for the Sky Islands Ecoregion.” Accessed February 28, 2021. https://databasin.org/datasets/7db2406c45114971abaad48483922d47/.
Brown, Jerram L. “Social Organization and Behavior of the Mexican Jay.” The Condor 65, no. 2 (March 1963): 126–53. https://doi.org/10.2307/1365491.
Cully, Jack F. “Comparative Mobbing Behavior of Scrub and Mexican Jays” The Auk 93 (1976): 10.
Brown, Jerram L., Esther R. Brown, and Joseph Sedransk. “Dominance, Age, and Reproductive Success in a Complex Society: A Long-Term Study of the Mexican Jay.” The Auk 114, no. 2 (April 1997): 279–86. https://doi.org/10.2307/4089168.
McCune, Kelsey. “Mexican Jays ( Aphelocoma Wollweberi ) Prey on Bats in Arizona.” The Southwestern Naturalist 61 (March 14, 2016): 146–48. https://doi.org/10.1894/0038-4909-61.2.146.
Strahl, Stuart D., and Jerram L. Brown. “Geographic Variation in Social Structure and Behavior of Aphelocoma Ultramarina.” The Condor 89, no. 2 (May 1987): 422. https://doi.org/10.2307/1368497.
Eimes, John Andrew. “Extra-Pair Fertilization, Mate Choice and Genetic Similarity in the Mexican Jay (Aphelocoma Ultramarina),” 2004.
Brown, Jerram L., and Esther R. Brown. “Are Inbred Offspring Less Fit? Survival in a Natural Population of Mexican Jays.” Behavioral Ecology 9, no. 1 (January 1, 1998): 60–63. https://doi.org/10.1093/beheco/9.1.60.
Tarvin, Keith A., and Glen E. Woolfenden. “Patterns of Dominance and Aggressive Behavior in Blue Jays at a Feeder.” The Condor 99, no. 2 (May 1997): 434–44. https://doi.org/10.2307/1369950.
Beaver, Bill. “Acorn Woodpeckers (Melanerpes Formicivorus).” Emergent Thoughts, February 7, 2021. https://wjbeaver.wixsite.com/mysite/post/acorn-woodpeckers-melanerpes-formicivorus.
Koenig, Walter D., and Ronald L. Mumme. Population Ecology of the Cooperatively Breeding Acorn Woodpecker., 1987. https://press.princeton.edu/books/paperback/9780691084640/population-ecology-of-the-cooperatively-breeding-acorn-woodpecker-mpb.
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