Posted by: davidlarkin | July 1, 2008

Avian Infanticide in Arizona – Grackle Family Life

“Oh, birds of Arizona, who woke me yesterday with your excited chirping, where do you go to die?”

— Billy Collins, “Lying in Bed in the Dark, I Silently Address the Birds of Arizona”

For twelve years, I have been feeding the birds of Arizona in my backyard in Chandler, a suburb of Phoenix. The smaller birds — the sparrows, house finches, mourning, white-winged and inca doves, red-winged blackbirds, brown-headed cowbirds, Abert’s towhees, curve-billed thrashers, and occasional feral parakeets, eat generic wildbird seed and black oil sunflower seeds in the feeders around the house and spread on the dry earth beneath the feeders, grassless from years of incessant pecking. The ubiquitous great-tailed grackles, 15 to 18 inch tall shiny black crow-like males with large square tails and sleek smaller gold-breasted females, eat dried seafood-flavored cat food that I throw across the lawn each morning. I purposely do not use the chicken-flavored cat food to avoid giving them a taste for bird. With their beaks pointing to the sky, the grackles hop across the lawn to dip and soften the crunchy chips in the large clear plastic birthday cake domes from the party store that serve as excellent water bowls. All the birds drink from the bowls, but the grackles, in addition to dipping anything they may try to eat, also use the bowls for bathing in the shade in the 110 degree Arizona heat.

When I first introduced the dried cat food, the grackles took to it immediately. For the first couple of years, I put the cat food on metal trays. The grackles would leap backwards after selecting a chip with a peck. I dropped the metal trays from the feeding program and about two years later, the mourning doves, European starlings, sparrows and Gila woodpeckers had learned to eat the cat food. Now they group by species each morning in a communal feeding frenzy after I leave the yard. Recently, I noticed a grackle taking a cat food chip from the grass and leaping backwards. Was this an old friend back again after ten years feeding elsewhere, still conditioned to leaping from the metal pans? Or maybe a child of a former customer who learned to eat with a leap from their parents?

The grackles have more than a dozen nests in the two large trees in my backyard, especially the evergreen Ficus in which I have counted at least ten nests spread through its leafy branches. The grackles are a community, sharing some duties. For example, if a baby grackle falls from the nest too soon, hiding beneath a bush, all the local grackles, males and females, will dive bomb me, screeching to scare me away, with the mother the most aggressive, of course. I have rescued a few babies, put them in a box open at the top outside overnight out of the reach of the local cats, only to find them gone the next morning, with no sign of any cat attack, apparently rescued by a parent. The fledglings who have left the nest fly with the mother for a few weeks. I see them on the lawn wildly flapping their wings with their mouths wide open waiting for the mother to hop over to feed them some cat food or some water. They fly away together. I have seen a male grackle feed the fledglings on a few occasions.

A few years ago, I went to fill the water bowls in the morning and found four dead baby grackles, all drowned in one bowl. Considering the circumstances of my backyard, only another grackle, a mother I assumed, could have killed them and left them in the bowl, but I could not imagine why they were killed. I emailed the Cornell Lab of Ornithology, but they were unable to provide an explanation. One friend suggested that the mother was depressed, but I could not locate a bird psychologist to question.

Recently, I was exercising on the treadmill, watching Robert Sapolsky, Stanford Professor of Neuroscience and a recipient of the MacArthur Foundation “genius” fellowship, give a Teaching Company lecture on the evolution of behavior. The evolutionary paradigm had changed over the past 50 years, Sapolsky explained. Marlin Perkins’ “Wild Kingdom” had shown in the early 60s how the heroic wildebeest would throw himself into the river, sacrificing himself to the crocodiles so the rest of the herd could cross the river while the crocodiles were distracted by their feast. The wildebeest did this, Perkins told us, for the “good of the species,” an evolutionary communal survival principle. Sapolsky explained that that “old principle” had since been proven false. In fact, he said, the younger stronger wildebeests pushed the weaker older one into the water for their own self-centered evolutionary purpose. The evolutionary principle of individual selection, optimization of the number of copies of an individual’s own genes, Sapolsky said, has replaced the old idea that individuals acted for the good of the species.

With gorillas, lions and some other mammals, a dominant male will have a harem and sire all the offspring of the group, with the other males living in an irrelevant bachelor group. Occasionally, another male will topple the dominant male from his throne. Grimly, the new dominant one will then kill as many infants as he can. This is not a Machiavellian political move, but a matter of individual selection: when the infant dies, the mother ceases nursing and soon ovulates. The new dominant male can then produce offspring with copies of his genes.

One thing I know about the great-tailed grackle from prior research is that, like gorillas, the dominant male grackle has a harem. While listening to Sapolsky’s evolutionary explanation of mammalian infanticide, it dawned on me that what I had likely seen in my backyard was the work of a new dominant male grackle committing infanticide, drowning four baby grackles in order to make a quicker start at producing copies of his genes. I do not know whether the hormonal impact on a mother grackle of the baby’s death is the same or similar to the impact on the nursing gorilla female, but obviously, the mother grackle will have more time to devote to the reproduction rites without the duties of feeding and caring for her babies. Research shows that there is avian infanticide, and although uncommon, most avian infanticide committed by males is directed at eggs, with a record of infanticide directed at fledglings occurring in a couple of species. With the help of google, I found in an obscure book entirely devoted to avian infanticide, one anecdotal account of infanticide by a male Tristam’s grackle, a species found only in the Arabian peninsula.

Answering Billy Collins’ poetic question — Where do Arizona birds go to die? — may be unpoetic, but now and then, infanticide aside, one of my Arizona birds randomly dies in my back yard in no particular place.

HERE IS A BABY GRACKLE REHABILITATED AND RAISED TO SURVIVE:

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Responses

  1. Dave — thanks — fascinating post.

  2. I had never heard of avian infanticide before – wow – bizarre.

  3. After keeping baby chicks a bowl of open water that they cannot get out of they can drown. I would have to put stones in the drinking dish to prevent such a happening. They were perhaps thirsty and drown falling in.

    • The nests were not near the water bowls. The grackle chicks were babies and were to young to fly or to walk to the water bowls. They were carried there and drowned by a wicked male grackle who wanted to start his own family.


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