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White-Throated Sparrow

7/14/2015

 
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Many of you know that the White-throated Sparrow comes in two forms: white-crowned and tan-crowned. What you might not know is why. First, the two colors rarely mate with each other. They follow the adage "opposites attract" rather than "birds of a feather". Males prefer females with white stripes, but females prefer males with tan stripes.

Second, the genetics roughly follow Mendel's infamous but simple pea plant chart (Punnett Square). In simple terms, Mendel noted that pea plants have round peas (R) or wrinkled peas (r), where R and r are two different alleles for a single trait. A heterozygous plant would carry both R and r (Rr). A homozygous plant would carry only RR or rr. If two heterozygous plants are bred, the four resulting offspring would have the following: RR, rr, Rr and Rr.

In the case of the White-throated sparrow, the tan form of the birds is homozygous (WW). The white form of the birds is heterozygous (Ww). The white stripe is inherited as a dominant trait. With this combination of genes, the way in which the different forms choose mates, and the difference in parenting behavior between the two color variations, the result is an approximate 50-50 split in the stripe color. We have approximately an equal number of tan-striped and white-striped birds ("Behavioral Characterization of a White-throated Sparrow Homozygous for the ZAL2m Chromosomal Rearrangement", Horton, et al, 2012).

An interesting side-effect of the difference in coloration is the level of aggression demonstrated by each color of sparrow. The White-throated Sparrows with white stripes are more aggressive than those with tan stripes. The white-striped birds also sing more, but the tan-striped birds are better parents ("Alternative reproductive strategies in the White-throated Sparrow: behavioral and genetic evidence", Tuttle, 2002). The birds are therefore becoming important subjects for scientists who want to determine whether behavior in organisms is tied to physical traits and if so, how and to what extent? It will be interesting to see what their studies suggest. 

White-throated Sparrows have also been known to hybridize with Juncos. They look just as you might imagine: a very dark bird with some striping like a sparrow, white throat, and white belly and outer tail feathers of a Junco. One such hybrid was captured in Maryland and studied extensively ("Behavior and Parentage of a White-throated Sparrow x Dark-eyed Junco Hybrid", Jung, et al. 1994). The bird sang a mixed song of a Junco trill followed by the sparrow "peabody" notes and seemed to prefer the company of female White-throated Sparrows over female Juncos. 

Next winter, when you're watching your feeders, take a close look at your White-throated Sparrows and take note of their coloration and behavior. 

Red-Bellied Woodpecker

7/13/2015

 
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I have had the pleasure of helping to band a Red-bellied Woodpecker. Their size and the length of their beak may seem fearsome, but they are far less aggressive when being extracted from the net than a Northern Cardinal. Cardinals will grab your skin with their beak and twist it! 

I was in for a pleasant surprise with this bird: I got a close-up view of its tongue! It's one thing to see a Red-bellied Woodpecker use that amazing tongue at your feeder, but it's a far different thing when that tongue whips out right in front of you. The length is unbelievable: about three times the length of the bird's beak. It resembles a weapon from a fictional apocalyptic movie: a long spear with multiple barbs facing backward toward the throat (like a harpoon on steroids), ending with a sharp point on the end, and coated with a sticky substance. It is a perfectly designed tool for extracting insects from their burrows, able to reach into a narrow opening, blindly search for and locate insects, and pull the insects out using the barbs and goo. In the case of a grub, the the sharp end of the tongue may be used to skewer its prey. "En garde! Oops. Too late." 

The beak itself harbors another weapon, this time used against unsuspecting nuts. The woodpecker cracks open nuts by using its beak as a hammer and a tree as an anvil. Wedging the nut into a crevice in the bark, the woodpecker pounds on the nut with its beak until the nut's shell gives way.

Nuts are one of the bird's favorite foods, but the other is insects. The Red-bellied Woodpecker is a voracious predator of some of our most harmful insects. One tree can contain 1,000 adult Emerald Ash Borer beetles. Woodpeckers have been observed consuming 95% of the larvae before they can emerge as adults, making them a natural and native biological weapon against these invasive and expensive pests ("Emerald Ash Borer in North America: a research and regulatory challenge", Cappaert, et al., 2005). A friend of mine, birder and naturalist extraordinaire Jim McCormac, wrote about the increase in the Red-bellied Woodpecker and its relationship to the Emerald Ash Borer: http://jimmccormac.blogspot.com/2013/12/woodpeckers-boom-probably-because-of.html In Ohio where Mr. McCormac resides, the CBC totals in 2012 showed a 55% increase in population of Red-bellied Woodpeckers since 2003. Indiana's 114th CBC had record numbers of Red-bellied Woodpeckers: 1929 statewide.

Red-bellied Woodpeckers are also painfully aware that it is prudent to save for a rainy (or snowy) day. They store food to sustain them during times that meals are hard to find. 

Now let's discuss the elephant in the room: the misleading name. People often mistakenly call this a Red-headed Woodpecker. It does have a red head after all, but the true Red-headed Woodpecker has a far more spectacular red head, so it claims that name. But what about the "red belly"? It's not often that you can see the reddish color on the bird's stomach while in the field. If you look very closely, you might see a reddish patch with a yellowish wash on the belly that looks as if someone dropped a dollop of paint on the bird and made a poor effort of trying to wash it off.

The invasive European Starling has been a constant source of irritation for our native Red-bellied Woodpeckers, evicting the woodpeckers from their nest cavities about 50% of the time ("Nesting phenology and competition for nest sites among Red-headed and Red-bellied Woodpeckers and European Starlings", Ingold, 1989). This video of a battle between a Starling and a Red-bellied Woodpecker over a nest cavity will make you cringe: https://www.youtube.com/watch?v=1x5W9w-fxik

    Author

    Alex Forsythe

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