CLAY-COLORED ROBINS
BUILDING NESTS
One of my favorite hiking destinations lies at
the far end of the reservoir, about 45 minutes away, where the valley narrows, the lake
becomes a trickling stream, and Bonpland Willows and Mexican Sycamores create a shadowy
woods. Livestock trails paralleling the stream take me through the woods. Beneath every
big tree there's always a comfortably rounded boulder you can sit on, and always the birds
are putting on a show.
 This week Clay-colored Robins have been
particularly vocal and busy. They hop on the ground tossing litter aside with their bills
just like American Robins. When worried about something they issue nasal clucks the way
nervous American Robins do, and their body shape and size is just like the American
Robin's. The only obvious big difference between the two species is that the
Clay-colored's drab plumage shows only hues of brown. At the right you can see one I
photographed another time in the Yucatán.
If your computer can handle WAV files you can hear one by clicking on the
"play" button on the blue thing here.
This week I watched a Clay-colored Robin starting the building of her nest with what
appeared to be dried-up willow rootlets left hanging on dry banks, now that the water is
so low. I read that the finished nest will have a middle layer of mud. The species lays
2-3 pale to bright blue eggs, and may produce two broods. I also read that Clay-colored
Robins eat earthworms, slugs, insects, fruits, and sometimes lizards. They follow army
ants and feed on small animals trying to escape the ant columns.
Clay-colored Robins are so reminiscent of American Robins that I just assumed that, as
with the American Robin, the Clay-colored male would claim and vigorously defend a
territory, while the female nested somewhere within it. Therefore, this week, what I saw
didn't make sense.
Around the tree where the female Clay-colored Robin was building her nest I saw three
other Clay-colors doing various things. Moreover, as I continued up the valley I passed
through several clusters of the species. I heard lots of singing and saw some courtship
behavior but most robins seemed to be doing nothing special. In fact, what stuck me was
that nowhere could I see territory-boundary disputes taking place, and clearly there were
no territories being claimed by exclusively male-female family units. This was a situation
to place before Google.
On the Internet I found no comprehensive description of Clay-colored Robin behavior,
but I did find brief references and side remarks that gradually presented a picture.
In an online article of the journal The Condor,at http://www.princeton.edu/~hau/ReprintLinks/2003Condor105.pdf
I found the Clay-colored Robin's social system described as "mating aggregations,
leks," and its territoriality as "short, local display court." In the same
paper I read that Clay-colored Robins "display in groups."
That word "lek" refers to an aggregation of males, each seeking to attract a
mate, and each displaying fervently. It's assumed that "lekking" groups attract
more females than do isolated males, and probably this helps the females better compare
their potential mate.
Another online article referred to Clay-colored Robins as "polygynous," and
yet another called them a "potentially polygynous (lekking) species." In
biology, polygyny is a mating practice in which the male takes more than one female sexual
partner.
Digesting these laconic and somewhat cryptic lines gradually I conjured an idea of what
I'd seen among the Clay-colored Robins that day.
I would guess that that morning the livestock trail along the stream took me through
one "mating aggregation" after another, each group consisting of one to several
females and a male, and maybe there were "surplus males" weaving in and out of
groups as opportunities arose.
That's just a guess, though. The only thing for sure is that at first glance
Clay-colored Robins may remind us a very great deal of American Robins, but by no means do
their mating activities come close to how Northerners expect a good robin to behave. |