Jim Williams has been watching birds and writing about their antics since before "Gilligan's Island" went into reruns. Join him for his unique insights, his everyday adventures and an open conversation about the birds in your back yard and beyond.
These are photos of a pair of Red-tailed Hawks mating. I've been watching this pair for about two weeks, ever since I discovered their nesting site. A few days ago I was fortunate enough to be on site and in the right place when their brief mating encounter took place. Both birds are using their wings for balance. The male is on top. The female has raised her tail and pulled it to the left. (Her tail is light, showing a reddish tint). In the first photo the male has his tail (dark rectangle) in its usual position as he mounts the female. To transfer sperm, the male also twists his tail to the left ( second photo) to facilitate contact of his cloaca with the female's cloaca. This particular encounter lasted about five seconds. Development of the egg in the female takes about 24 hours. The female will lay one egg per day until she has a complete clutch of one to five eggs. Incubation takes from 28 to 35 days. If the egg has markings, those are deposited on the shell during its passage through the uterus. Rapid movement through the uterus produces streaks of color, slower movement spots. Red-tailed Hawk eggs are white or buffy, marked with buff, brown, or purple.
A Great Horned Owl nest holding the hen and two chicks can easily be seen at Silverwood Park in St. Anthony. (Park personnel have established a limit to approach to prevent disturbing the birds.) The hen and her chicks are nesting in the hollow of a broken branch in a large tree very close to a paved walking path, about 30 feet up. Visitors should have no problem locating the birds. Just look for the photographers, ever-present at this unusual viewing opportunity. The young owls appear to be about six weeks old. The male owl often can be seen perched, sound asleep, high in a nearby tree. That bird, as you can see from the photo below (not a very cooperative bird) is much lighter than its mate. Coloration of this species is highly variable. This female has typical adult coloration. The male tends more toward the lighter birds found most often far north. Great Horned Owls can be so light as to resemble Snowy Owls. This one is far from that, but interesting nonetheless. The owls should be visible for several more weeks. Once the young birds leave the nest they often remain in its vicinity. To find them, drive to the park’s most distant parking lot. There is a paved walkway leading between two park buildings. Follow that pathway approximately 200 yards. You might also find interesting the courtship behavior of at least seven Eastern Chipmunks in a tangle of brush and fallen logs immediately to the right of the walkway from the best owl-viewing spot. Friday, they were chasing each other incessantly. The chipmunks are very obvious right under the eye of the female owl. The male owl, the family’s provider, sleeps during the day, hunting at night. Perhaps that explains the mammals’ apparent daytime nonchalance.
Shortly after I was given the Chimney Swift nest last month (see previous post), I found the nest of a Northern Cardinal. Compared to the craftsmanship of the swift’s, cardinals build with less precision. Ragged comes to mind, although in defense of the cardinals their work weathered for several months before I found it. This nest is made of sticks and leaves, grape-vine bark, unidentified vine pieces, and strips of cellophane. I found it in a Buckthorn tree (Buckthorn should never be allowed to grow to tree size). It’s the first nest I’ve seen in Buckthorn, and that put it rather in the open. The other two cardinal nests I’ve seen were tucked in the middle of large and thick bushes, almost impossible to see. Above, the cardinal nest. Below, for comparison, the swift nest. Cardinals twist and weave their materials, while swifts use their saliva for glue.
The chimney that provided me with a Chimney Swift nest last year has done so again. A friend helped me Wednesday morning take photos of and then remove the nest from the chimney. That involved some gentle pry work with a spatula. These birds have adhered their nests to the brick surface just above the fireplace floor and just below the metal chimney liner. A rough surface is needed for nest placement. The birds’ saliva is the glue that holds the nest in place and together. The nest sat about 10 feet down from the chimney opening and two feet above the fireplace floor. It was easily reachable. The chimney lining is evident in the photo. We’re looking at the nest from the bottom. What appears as the bottom edge of the nest in the photo is actually the front lip of the nest. The nest was surprisingly shallow, and had a slight downhill slant. The nest projected three inches from the brick, and is four inches across. The cup that held the young birds — normally four in number — has a diameter of about two inches. That’s pretty cozy. This nest held some egg shell pieces. There was no evidence on the fireplace floor of birds ever using the chimney. Young swifts produce their waste in fecal sacs that are removed by the adult birds. The birds, their sounds first mistaken for bats, could easily be heard while the nest was active. The swifts have returned to this chimney for several years without a miss.
Cowbirds and buffalo might not be as closely involved as we think.
Two weeks ago the birding column in the Home and Garden section of the StarTribune focused on cowbirds. I repeated the commonly held belief that cowbirds adopted their brood-parasite habit via their relationship with buffalo. Cowbirds fed on the insects and seeds disturbed by buffalo herds. Since those herds were always on the move, cowbirds could not nest in the usual fashion. While the birds were incubating and feeding hatchlings, the buffalo were moving on. So, it has been believed, cowbirds evolved into brood parasites: birds that lay their eggs in the nests of other birds, letting the host hatch and raise those chicks.
Roger Everhart, a birder in Apple Valley, wrote to tell me of new information that casts significant doubt on that idea. HIs information comes from an email post made to a national birding chat line by Alvaro Jaramillo, a senior biologist at the San Francisco Bay Bird Observatory. Jaramillo wrote of study of cowbird DNA by Dr. Scott Lanyon, professor and head of the Department of Ecology, Evolution, and Behavior at the University of Minnesota.
The upshot is the suggestion that Brown-headed Cowbirds, while they did follow buffalo herds, were parasitic before they ever found buffalo. This suggestion is based on age of the cowbird lineage, as determined by the DNA study. Jaramillo wrote, "Parasitism in the cowbirds may have evolved due to coloniality, and the safe predator-secure nests of the hosts, among other factors." (Coloniality: birds nesting in colonies.)
Jaramillo continued, "Basically, it (the evolution of brood parasite behavior) is still a mystery. However, the fact that brood parasitism has evolved in several unrelated groups such as cowbirds, two cuckoo lineages, many other birds, and even aphids it is clear that this is a good way to make a living."
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