A future relict snack?
On a lighter note (sort of), last week was my final week of winter break, which I usually spend sulking around my house in despair over the days to come, when birds and sunlight are but distant memories of life in the 'before time'. This year I opted to change this depressing pattern, even if it meant simply getting out of the house in search of birds that I had little chance of finding.
First winter White-throated Sparrow
Inspired by my luck on the Waterloo Christmas Count and Joyce Peterson's find on the Albion Christmas Count, I started out the week searching for Yellow-rumped Warblers in Jackson County. Based on observations of this species in southern and central Michigan during this winter, it appears that they tend to prefer shrubby, riparian areas with a good supply of berries (particularly poison ivy) and open water. As luck would have it, such habitat exists mere minutes from my house at Ella Sharp Park. But despite perfect habitat, I came up empty on butterbutts, though the place was loaded with White-throated Sparrows, which I haven't been able to find anywhere else in the county.
Adult, (putative) tan-striped morph
Within the four or five flocks I encountered, I only saw a couple of white-striped individuals, which seemed odd (though many may have been first year birds that simply haven't molted yet). White-throated Sparrows exhibit a polymorphism that shows variation in morphometrics, behavior, and, most noticeaby, plumage (specifically in the crown stripes) (Lowther 1961). Interestingly, this polymorphism has been linked to a very large inversion on the second chromosome that contains about 1,000 genes (Thorneycroft 1966). Because inversions suppress crossing over (review your meiosis!), this means that the genes within the inversions that 'cause' the different morphs never get mixed together, allowing these sections of the genome to diverge from each other. What's perhaps even more interesting is that individuals of this species almost always mate with an individual of the opposite morph (Falls & Kopachena 2010), a behavior that may be influenced by this very region of the genome. Because of this, both morphs are stably maintained within the species and speciation has not occurred, even though this large area of the genome is diverging. When you consider that this inversion is thought to have occurred around 2.2 million years ago (Thomas et al., 2008), and that it causes many substantial differences in behavior and morphology, it is easy to imagine that, without this quirk of mating behavior (disassortative mating), we might very well have had another Zonotrichia species in North America! Science is fascinating.
After failing to find a butterbutt and having my camera die just before finding a huge flock of American Robins and a Hermit Thrush, I headed home to recharge my spirits and batteries before heading out again, this time with a more realistic goal -- Swamp Sparrows. I don't know that I'd ever seen a Swamp Sparrow in the winter, though I certainly know they're around in small numbers. I opted to first look in an area where flooded hardwoods borders cattail marsh near my home, which has been good for sparrows in past years. Much to my surprise, the Field Sparrow pictured above was the first sparrow I saw. I assume this is probably a bird from the consistent flock I've posted about previously, given the close proximity between locations. Interestingly, while the flock is incredibly skittish and difficult to observe in the nearby meadow, this bird was foraging on Reed Canary Grass (I think?) seeds just a few feet from me, paying almost no mind to my phishing efforts directed at his (her?) evolutionary cousins. This seemed like curiously bold behavior, given that this individual was apparently not in the company of any other birds.
No sooner had I forgone my efforts to stir up any other birds when this Song Sparrow and two others started cheking away at me, all while skillfully managing to prevent any decent photographs from happening on their behalf. Curiously enough, it appeared that the Field Sparrow did react to the calls of the Song Sparrows by taking evasive action into thick shrubs.
With all sparrows out of sight, I decided to play a few chip notes from a Swamp Sparrow, just to see if one was lurking in the cattails. Five seconds of the clip hadn't yet passed when this individual sprang up from a patch of grass, chipping away at my iPhone with the exact same calls that I was broadcasting. I don't know that I'd ever noticed it before, but it appears that Swamp Sparrows have much thinner bills than Song Sparrows. Interesting.
American Tree Sparrow
Just before I decided to head home, a flock of about ten American Tree Sparrows came dashing into the area and immediately took to foraging all over the place, including on the ice. A few minutes after the cheerful, metallic chip notes of this flock had been bouncing all over the place, the Song Sparrows and Field Sparrow came out of hiding and joined the group in foraging on top of logs and in grassy patches around tree trunks, though they never strayed far from cover unlike the bold denizens of the Canadian tundra (perhaps a name change is in order).
I originally intended to add details about another unsuccessful warbler quest (this time for Common Yellowthroats), but realized that it would amount to little more than me continuing on about sparrow behavior. In an attempt to keep you from not ever wanting to look at future posts containing sparrows, I'll just post a few pictures from the day.
One of about ten at Cascades Park
One of about five
How can you not adore chickadees?
...I mean, seriously.
One of many!
One of at least six on the Hoffman Trail
Is there a better looking woodpecker in the eastern forest?
Falls, J. B. and J. G. Kopachena. 2010. White-throated Sparrow (Zonotrichia albicollis), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/128
1961. Polymorphism in the White-throated Sparrow, Zonotrichia albicollis (Gmelin). Can. J. Zool. 39:281-292.
2008. The chromosomal polymorphism linked to variation in social behavior in the White-throated Sparrow (Zonotrichia albicollis) is a complex rearragement and suppressor of recombination. Genetics 179(3):1455-1468.
1966. Chromosomal polymorphism in the White-throated Sparrow, Zonotrichia albicollis (Gmelin). Science 154:1571-1572.