How can they tell the boys from the girls?

Written by Jack Sanders
Thursday, 15 March 2012 10:50

Philip Tulimieri of Darien recently photographed this Red-bellied Woodpecker on a feeder. Like their cousins, the Pileateds, Red-bellies may be seen “frozen” to the sides of trees, reader Nora Gordon reports in this week’s column.In many species of birds, the difference between male and female is obvious: The sexes are marked and/or colored differently. But in many others, likes crows, titmice and chickadees, both sexes seem identical, making it almost impossible for us to tell them apart.

Markings can, indeed, make a difference to the birds themselves, as was shown by experiments with Northern Flickers. The male and female flickers of the yellow-shafted “morph” are quite similar, except that the male has a black line near the base of the beak, and the female has no black line. Biologists captured the female of a mated pair, and painted a black mark near the beak, making it look like a male. The female was released and went to its nest. When the male returned to the nest, it immediately tried to chase the female away. However, it soon realized from the behavior of the mate that it was, in fact, its female companion.

Birds whose outward appearance is the same in both sexes are a challenge for humans. Crows are so difficult to tell apart that, unless there is some obvious sign like position in copulation, even ornithologists cannot distinguish one from the other. 

But obviously crows can tell boys from girls. To determine sex they probably rely on behavior such as how the other bird acts when approached. For instance, male birds tend to be aggressive toward one another while females faced with aggressive behavior tend to retreat. 

Males and females may have differences in movement or poses that are difficult for us to detect, but are obvious to crows.

Song variations can determine not only the species, but the sex in many kinds of birds. Females will respond only to males of the same species. Among similar species, song variations can help prevent crossbreeding and hybridization, which may result in aberrant offspring that are less able to succeed in finding mates.

In many kinds of creatures, scent helps give away the sex of individual. However, almost all birds are believed to have limited senses of smell, so scent probably does not play a role in sexual attraction.

Incidentally, immature birds of species that have differently colored adults are often hard to tell apart. For instance, male and female cardinals look identical as juvenile birds. 

This is probably because, until they are old enough for mating, there is no need to have different coloration. Instead, immature birds often bear colors and markings that are better for camouflage than for showing off because the young are less savvy about predators and need that extra protection. 

Frozen woodpeckers

Nora Gordon of Ridgefield read the recent column about the Pileated Woodpecker seen “frozen” to a tree trunk and offers another theory on why a woodpecker may cling to the side of a tree for a long time, without moving.

“I have had a pair of Red-bellied Woodpeckers that come to my feeders.  One day I was watching the female pecking the side of a tree.  When next I looked at her, she was stock still, ‘hugging the tree’ for quite some time.  She wasn’t cocking her head to look for a hawk, nor did I see any around.  

“I thought it was peculiar, but then she dropped down about her body length, and began pecking at the bark.  

“It seemed to me she was using her body heat to stir up some grub!? Perhaps that was what the Pileated was doing also?”

It’s an interesting theory. The body heat of a woodpecker is well sealed in by its feathers and it probably would not warm a winter tree much. However, it could be just enough to stir activity right at the surface among hibernating insects.

There is still another possibility that came to mind after reading Nora’s idea: Some ornithologists believe that woodpeckers “listen” to trees and logs for signs of insect activity within. Dr. Thomas S. Roberts, a physician who was also an ornithologist, wrote in a 1932 report on Hairy Woodpeckers, “There has been considerable discussion as to how the woodpeckers locate the larvae, active or dormant, which are hidden deeply in the wood and for which they drill so unerringly. ...The active grub, as it crunches the wood, makes a sound that would surely be audible to a bird with its keen sense of hearing.”

Coming up

Family Nestbox Workshop, hosting bird families in your yard, kits can be ordered, Saturday, March 17, 2 to 3:30 p.m., Audubon Greenwich, 613 Riversville Road, Ted at 203-869-5272 x230. 

Woodcock Watch, one of the rites of spring, Saturday, March 17, 6:45 to 7:45 p.m.   $5, Audubon Greenwich, 613 Riversville Road, RSVP  to Jeff at 203-869-5272 x239.

Eagle Viewing Trips, on Connecticut River, through March 18, 9, 11:30 and 2 on weekends, and 10 and 1 on Thursdays, $40, Connecticut Audubon, 1-800-996-8747

Annual Meeting, Connecticut Ornithological Association, with sessions on gull identification and watching, interesting lives of local species, innovative approaches to birding, more, Saturday, March 24, all day, $20/$25, open to public, but registration required, Chapman Hall, Middlesex Community College, Middletown, ctbirding.org.

Bird Watching 101, “a good foundation for enthusiasts,” Saturday, March 31, 1 to 3:30 p.m.,  $15/adult, kids free, Audubon Greenwich, 613 Riversville Road, RSVP  to Ted at 203-869-5272 x230.

Seals and Seabirds cruises, two and a half hours around Norwalk Islands, Saturday,   March 31 at noon and Sunday, April 1, at 1 p.m., $20.50, Maritime Aquarium, Norwalk, 203-852-0700, ext. 2206, maritimeaquarium.org.

Copyright 2012 by Jack Sanders. Send sightings or comments to: jackfsanders [at sign] gmail.com, or to Bird Notes, Box 1019, Ridgefield, CT 06877. If you need help identifying a bird, try your local nature center. If you find an injured bird, call wildlife rehabilitator Darlene Wimbrow of Redding, 203-438-0618, Wildlife in Crisis of Weston, 203-544-9913, or Wild Wings of Greenwich, 203-637-9822. The columnist’s website is www. sandersbooks. com.