Evolution 2016: Mammals

by Greg Mayer

I spent June 17-22 in Austin, Texas, for Evolution 2016, the annual joint meeting of the Society for the Study of Evolution, the American Society of Naturalists, and the Society of Systematic Biology, which is the premier annual gathering of evolutionary biologists from around the world. I hope to make a few posts about the goings on, and we’ll start with some natural history.

On the day I arrived I met up with my friend and colleague Steve Orzack, and we headed out to Pedernales Falls State Park, about an hour west of Austin, to do some birding and herping prior to the official kickoff of the meeting that evening. Also keeping an eye out for mammals, I noticed a sign mentioning “rock squirrels”, showing a black headed squirrel, and recalling how variable fox squirrels are, I wondered if this might be the local variety of fox squirrels. We soon came across a squirrel, which, however, was a rather interesting Eastern gray squirrel (Sciurus carolinensis).

In the northern United States, gray squirrels are typically gray above and white below, while fox squirrels are a slightly different shade of gray above and fulvous below. Very rarely a gray squirrel may be fulvous below, in which case the definitive character to look for is that gray squirrels have a white frosting or “halo” on their tails (the tips of the outer tail hairs being white). The squirrel above caught our attention because while gray above, it’s clearly ochraceous buff below, so I thought it might be a fox squirrel. We kept it under observation, and it soon showed its true colors.

Obligingly raising its tail while stopping to drink out of small puddles and pools in the spring-fed muddy track along which we walked, it revealed its gray squirrel-defining frosting on its tail, while also clearly showing it was reddish below.

I’ve never seen gray squirrels in the north drink like this, and it may reflect the scarcity of water sources in the dry scrublands of Texas. This squirrel was also of interest because the park is in Blanco County, and according to Texas Tech, Blanco County is just outside the range of the gray squirrel, so this would be a new county record. (The rock squirrel of Pedernales Falls turns out to be a rather bushy-tailed, black-headed ground squirrel, Spermophilus variegatus, but we did not see any).

The reddish ventral coloration was not a peculiarity of this individual, for the urban squirrels of Austin were also gray squirrels with ochraceous buff venters. This guy was hanging out at one of the bars on Rainey Street.

This one was in the parkland strip along Lady Bird Lake (actually an impounded strip of the Colorado River) just west of Rainey Street. The ochraceous buff venter is clearly visible.

This particular squirrel was first spotted with a mixed flock of great-tailed grackles, white-winged doves, and rock doves. Try spotting all four species in the picture below

Austin’s most famous mammals are the Mexican free-tailed bats (Tadarida brasiliensis) that roost under the Congress Avenue Bridge, and emerge by the millions (or so I am told) each evening. I went out twice to see them, once from below the bridge, and once from the sidewalk above; they came out about 9 PM. Both times large crowds gathered both above and below, and many vessels, including tour boats, gathered on the lake below the bridge. Attempts to photograph them were unsuccessful with my limited camera, but you can see them briefly in the video; listen for the murmur of the bats in the background behind the voices. The red light is a search light used by one of the tour boats, and I tried to follow this light to catch the bats on the video.

On the last day of the meetings, I walked under the bridge to get to the concluding Super Social, and found this dead bat below the bridge. You can clearly see its ‘free tail’ (i.e. the tail is not completely contained within the membrane of the uropatagium).

The deposits of bat-feces rich sediments (bat guano) below bat roosts (especially if in caves) are often important sources of fossils of bats and associated creatures; there’s a ‘rain’ of dead bats into this sediment. But with a lake and sidewalk below, this cute fellow is unlikely to be fossilized.

The pièce de résistance of the mammals of Austin for me was a new species and family of mammals for my life list: I spotted a coypu (Myocastor coypus) swimming down Waller Creek in the heart of downtown Austin, right behind Iron Works BBQ. The coypu (or nutria) is an invasive species, originally brought to the U.S. from South America. They look like large muskrats, but do not have a laterally compressed tail. I was looking for the tail, which I could not see clearly, but once I looked at my pictures and video I could easily see the distinctive, diagnostic whitish snout of the coypu.