Why Evolution is True is a blog written by Jerry Coyne, centered on evolution and biology but also dealing with diverse topics like politics, culture, and cats.
Because of a paucity of readers’ wildlife photos (I do have some, so if you sent them have patience), I’m deferring posting those till tomorrow, replacing them with a SQUIRREL CENSUS post by Greg:
by Greg Mayer
We’ve long been fans of squirrels here at WEIT, and so I was quite pleased to come across the following item in the New York Times, a combination of text, audio, video, and stills, on a census of the gray squirrels (Sciurus carolinensis) in Central Park. (Be sure to have the sound on for the squirrel vocalizations.)
And it’s not just because it’s squirrels– it’s the location, too. Research takes me every year or two to the American Museum of Natural History, which is located on Central Park West between 77th and 81st Streets, and I often walk across to Central Park to have lunch, where I enjoy the wildlife, including the squirrels. Mike Klemens of the American Museum did a herpetological inventory of Central Park, which I’ve remarked upon here at WEIT (the only herps I’ve ever seen are turtles in Turtle Pond), so I’m glad to see the squirrels get their due.
The Times also had two earlier articles about the start of the census, here
and here:
Going through the multimedia piece on the results of the inventory, I noticed this photo. . .
. . . of a melanistic squirrel in the Park. This is interesting for two reasons. First, I didn’t know there were black squirrels in Central Park—I’ve never seen one. (In New York City, “black squirrels” are a color form of the gray squirrel; in other places, the “black squirrels” may be fox squirrels, Sciurus niger.) Second, it shows that the black squirrels are not all blacks (sorry, New Zealand!), but usually have some reddish color in them. In the one above, the belly is quite extensively reddish; in black squirrels I’ve gotten close enough to see, there’s usually some red color on the back, although their appearance depends on the lighting; and from a distance they may appear all black.
I was hoping to look at the report of the squirrel census to see the prevalence and distribution of the black squirrels (as well as to find other fun squirrel facts), but was disappointed to find that the report will cost you $75! But, a single ring chart was visible on the census website—in a copy of the report opened to show what you would be paying for—and this chart shows that there were 140 black squirrels out of 3938 squirrels whose color was recorded: a frequency of 3.56%. (There’s also mention of a more common “cinnamon” morph, but I’m not convinced that’s a distinct morph.)
The Times piece also provided some bits of data. From the following figure, I was able to determine that of 2969 squirrels with a known color depicted, 103 were black, for 3.47%. (The “white” squirrels in the figure, 54 of them, are actually blanks—squirrels with no color data recorded. The pie chart had 74 such missing-data squirrels.)
I’m not sure why there are 3023 squirrels total in the Times‘ figure, but 4012 in the ring chart, but the two estimates of the prevalence of the black phase, 3.56 and 3.47%, are very close. It’s no wonder then, that the handful of squirrels I would see during my Central park rambles would not include any black ones.
In a nice “squirrel map” of all the sightings in Central Park in the Times piece, there are about 3 or 4 black squirrels recorded in the part of the park between the American Museum and the Turtle Pond, so they do occur there, but, again, at low frequency, so no surprise I haven’t seen them.
A trip to San Diego last month gave me the opportunity to check out the squirrel situation there. The native vegetation is coastal sage scrub and chapparal, with oaks and pines in higher and wetter areas, and desert to the south and west—very different from the deciduous woodlands of eastern North America which so many squirrels call home. The vegetation of San Diego has been greatly modified by man, however, with introduced species now dominating the cityscape– Eucalyptus (from Australia) and exotic palms (from everywhere) are omnipresent.
On the second day of our visit, we hit squirrel pay dirt in Balboa Park, a large urban park with little or nothing of its natural vegetation remaining. Appropriately enough, the squirrel was an introduced species, the fox squirrel, Sciurus niger. They were first recorded in San Diego in 1929.
Fox squirrels (Sciurus niger), Balboa Park, San Diego, California, 16 January 2019.
This pair was just outside the park’s visitors center. In the picture below, you can see the underside of the tail clearly. In Wisconsin, the shadings of the tail are the most reliable way to tell gray squirrels (Sciurus carolinensis) from fox squirrels– gray squirrels have white-tipped tail hairs, giving a ‘halo’ effect. Fox squirrels are very variable geographically, however, and this character may not work in all places, and I’m not sure where the San Diegan fox squirrels came from. (In a post here at WEIT a few years ago, I identified some squirrels from Texas as gray squirrels, but, given fox squirrels’ variability, I am now unsure of their identification.)
Fox squirrels (Sciurus niger), Balboa Park, San Diego, California, 16 January 2019.
A third fox squirrel, also outside the visitors center, sat in a classic squirrel pose.
Fox squirrel (Sciurus niger), Balboa Park, San Diego, California, 16 January 2019.
On another visit to Balboa Park a couple of days later, I was able to get up close and personal with this guy, and needed to use flash, hence the red-eye.
Fox squirrel (Sciurus niger), Balboa Park, San Diego, California, 18 January 2019.
The eastern gray squirrel (Sciurus carolinensis) was also introduced to Balboa Park, in 1924, but has apparently disappeared. During an 8-day stay I saw fox squirrels only in Balboa Park, not in other parts of the city. The native western gray squirrel, Sciurus griseus, is found only in the mountains in San Diego County.
Cities in the eastern half of the United States often have tree squirrels as a prominent element of their urban fauna. In much of the northeastern quadrant of the country, the “city squirrel” is the eastern gray squirrel, Sciurus carolinensis. From personal observation, this species is the city squirrel of Boston, New York, Washington, DC, Chicago, Milwaukee, and Madison, WI. As you head to the south and west, however, another species of tree squirrel, the somewhat larger fox squirrel, Sciurus niger, becomes a possibility. It is the city squirrel of Springfield, IL, and, quite exceptional for being so far to the north and east, Ann Arbor, MI. (On one of my first visits to that city, I remarked to someone that the city had the biggest gray squirrels I’d ever seen, and they replied, yeah, that’s because they were fox squirrels!) Both of these eastern species have been widely introduced elsewhere, the gray squirrel even overseas, including Great Britain and Ireland.
To see native squirrels, we had to go to San Ysidro, the southernmost part of the city of San Diego, on the Mexican border. As we walked to the border crossing there, we saw, on the slope to the east of the pedestrian approach, a modest colony of California ground squirrels, Spermophilus beecheyi. The white patch on the shoulder, extending somewhat in a line on the flank, is diagnostic; and in the out-of-focus individual in the background you can, paradoxically, see more clearly the dark area from the head onto the nape that separates the two shoulder patches. Note that someone seems to have thrown them a peanut (chewed on shell at left).
California ground squirrels (Spermophilus beecheyi), San Ysidro, California, 17 January 2019.
Ground squirrel tails tend to be less bushy than tree squirrel tails, but this species’ tail is fairly bushy. From the angle in the picture below, the squirrel even looks a fair amount like an eastern tree squirrel, since you can’t see its shoulder and nape.
California ground squirrel (Spermophilus beecheyi), San Ysidro, California, 17 January 2019.
In the next picture, we see a broader view of the colony, with scant, scrubby vegetation, including cactus; there were some scelrophyllous shrubs, as well. Bonus question: How many squirrels can you spot?
California ground squirrels (Spermophilus beecheyi), San Ysidro, California, 17 January 2019.
The ground squirrels also occurred just over the border in Tijuana.
California ground squirrel (Spermophilus beecheyi), Tijuana, B.C.N., Mexico, 17 January 2019, with Rock Doves (Columba livia).
There are many species of ground squirrels in western North America, but none in the east. (The easternmost is the thirteen-lined ground squirrel, which reaches the Midwest.) Many of these ground squirrels have more geographically or habitat restricted distributions. The white-tailed antelope squirrel, Ammospermophilus leucurus, is a desert species, which in San Diego County is found only in the eastern part of the county. The one below is in an exhibit hall, Coast to Cactus, at the San Diego Natural History Museum, devoted to the various biotic communities of southern California. It is a model, not an actual specimen.
White-tailed antelope squirrel (Ammospermophilus leucurus), model, at San Diego Natural History Museum.
And, to enlarge this account to include all of my encounters with incisor-enhanced critters in San Diego, here’s a Desert cottontail, (Sylvilagus audubonii), also in Balboa Park. Despite the common name, this is a common rabbit in a broad range of habitats, including urban-suburban ones, in San Diego.
Desert cottontail (Sylvilagus audubonii), Balboa Park, San Diego, California, 16 January 2019.
The San Diego Natural History Museum has been a leader in providing online access to its publications, collections, and exhibits, and for mammals there are a number of resources, and I’d point in particular to the various guides listed here, their checklist of the mammals of San Diego, and Suzanne Bond’s annotated list. They have recently published a truly excellent atlas of the mammal of San Diego, which I was able to consult while in San Diego, but not while writing this post, so if you’re interested in the exact details of the introductions and distributions of the species mentioned, you should consult the Atlas.
Bond, S.I. 1977 An annotated list of the mammals of San Diego County, California. Transactions of the San Diego Society of Natural History 18(14):229-248. pdf
Reid, F.A. 2006. A Field Guide to Mammals of North America. 4th ed. Houghton Mifflin, Boston. (The Peterson series mammal guide, and an excellent one; by browsing it, you can get a good overview of mammal distributions in the U.S. and Canada.)
Tremor, S., D. Stokes, W. Spencer, J. Diffendorfer, H. Thomas, S. Chivers, and P. Unitt. 2017. San Diego County Mammal Atlas. San Diego Natural History Museum, San Diego. Museum Store
Pulling into the parking lot behind my office this morning, an eastern gray squirrel (Sciurus carolinensis) sat in the middle of the road, blocking my way. This is an unusually bold posture for a squirrel– they are usually darting across roadways and parking lots: perhaps it knew it was Sunday, and wasn’t expecting any traffic? (This parking lot is not much used on weekends.) After a brief defiance, it relented and dashed off, which is when I saw the object of its mid-road attention– a treat:
It’s chocolate covered, looks like it might be peanut butter inside, and about 4 inches in diameter. The “chewed” side seemed more definitely chewed, with tooth marks, when viewed in person, than it does in this photo. I went out about 2 hours later, and the treat was gone. Presumably, the squirrel came back and absconded with it into the woods, which is a better place for squirrels to sit and eat.
I’m not sure if chocolate is good for squirrels. Chocolate is full of alkaloids, and unhealthy for some animals. I do, however, vaguely recall that squirrels in Costa Rica will eat cacao pods off trees, and this abstract seems to confirm that recollection. The tropical squirrels are in the same genus, but a different species, than the eastern gray.
Here in the U.S. it’s election day, and Americans are going to the polls to vote (many have already cast ballots in early voting). To divert you while awaiting the results (we’re expecting them at 3:00 PM Chicago time), here are a couple of items.
First, the following photo is of identical twins. Does it look like they are? Think about it first, and then post your thoughts in the comments. I’m sure most readers will figure it out.
Identical twins.
Second, my correspondent in Yokosuka, Japan, sends the following photo, and comments, “If I told you I just got a rugby playing squirrel from a vending machine in a camera store you’d think it was weird, but then remember I’m in Japan…. I especially like how the nut is the ball.”
A rugby-playing squirrel from Yokosuka, Japan.
The squirrel seems to be stretching for a try. If anyone can read the accompanying brochure, please translate it for us. I didn’t realize rugby was well enough known in Japan to be the subject of toys, but rugby is popular in a number of places you might not associate with the sport.
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).
Eastern gray squirrel at Pedernales Falls State Park, Johnson City, Texas, 17 June 2016
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.
Eastern gray squirrel at Pedernales Falls State Park, Johnson City, Texas, 17 June 2016.
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.
Eastern gray squirrel on Rainey Street, Austin, Texas, 19 June 2016.
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.
Eastern gray squirrel, Austin, Texas, 21 June 2016.
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
Mixed feeding flock of rock doves, white-winged doves, great-tailed grackles, and an eastern gray squirrel, Austin, Texas, 21 June 2016. Can you spot all the species?
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).
Mexican free-tailed bat, Austin, Texas, 21 June 2016.
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.
Mexican free-tailed bat, Austin, Texas, 21 June 2016.
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.
Squirrels are, of course, perennial favorites here at WEIT, being known as honorary cats. They also present a number of interesting phenomena of within and among population variation in easily observable traits like pelage color. Because these variations are often known even to casual observers, I often use squirrels as examples when explaining what species are. In eastern North America, gray squirrels, fox squirrels, ground squirrels, chipmunks, and woodchucks provide many informative examples of the differences within and among species.
We’ve had occasion to comment here on albino, parti-colored and blacksquirrels, all of which are gray squirrels (Sciurus carolinensis). I was thus intrigued when my Toronto correspondent sent along a photo, taken in Port Huron, Michigan, of a black squirrel with a brownish tail.
Gray squirrel that is black with brownish tail.
The body looks like a typical melanic squirrel– black, although when seen up close, they often have some reddish/brownish in them– but the tail is brown! Black is usually the result of the pigment eumelanin, while browns and reds often are due to the presence of phaeomelanin, so melanics can have both pigments present. In the Port Huron squirrel, the tail (although not the underside of the base, which is black) perhaps has only phaeomelanin. There were “tons” of regular melanics in Port Huron, but just one with the lighter tail.
I have seen melanics and albinos in the wild, but I had never seen– in the wild, in a museum, or just in a photo– a melanic with a brown tail. I consulted a colleague with a great deal of field experience in Wisconsin, especially northern Wisconsin, and he too had not seen them. I was surprised to learn after consulting a standard reference (Fiona Reid‘s volume on mammals in the Peterson Field Guide series– highly recommended) that such squirrels are in fact well known, especially from further north in the range of the squirrel.
My Toronto correspondent also sends a photo of a black squirrel from Toronto itself. Black squirrels are quite common in Ontario: my correspondent writes, “[I]n Toronto, I feel as if I see a black squirrel every time I turn around!” The interest of the pictured squirrel is that it seems to have light spots on the forehead and back; she said it looked “spotted”.
Spotted black squirrel in Toronto.
You can see the white spot on the forehead; there’s another, just barely visible in this photo, in the middle of the back. I have never seen this pattern either. I did find though, through a link provided by Jerry, the opposite pattern: a photo of a white squirrel with darker spots on forehead and mid-back from Brevard, North Carolina, where white (and mostly white) squirrels are common.
A Brevard, NC white squirrel with some dark markings on forehead and mid-back.
More kibbles have fallen into my lap: Greg has a post on Squirrel Week, which begins in April, but he wants it posted now because there’s a squirrel photo contest whose deadline is isoon. I should add that Greg’s daughter went to the Naval Academy in Annapolis Maryland, explaining his disquisition on Academy squirrels below.
by Greg Mayer
We are, dare I say, blessed to have not one, but two squirrel-themed holidays, National Squirrel Appreciation Day (January 21, which Jerry noted here), and Squirrel Week (April 12-18 of this year). The latter holiday seems to have been invented in 2011 by sciurophile Washington Post columnist John Kelly, who has announced Squirrel Week’s second annual photo contest. Entries are due by Mar. 27, and the winner will be announced on April 12. You should go have a look at the 2014 entrants, including the winner; Jerry highlighted some of these last year.
We’ve long had an interest in squirrels at WEIT, and John Kelly seems not to have said exactly when Squirrel Week is this year (the winning photo will be announced around April 12), so we’ll get an early start with gray squirrels (Sciurus carolinensis) from the U.S. Naval Academy in Annapolis, Maryland.
This is a retro-photo, from the 1970s. Squirrels are very common on the grounds of the Academy (which has many large deciduous trees), and are known there as “yard dogs”; we’ve seen them here before at WEIT. There are also cottontail rabbits (Sylvilagus floridanus) on “the Yard” (as the grounds of the Academy are called), and I call them “yard cats”. I asked an Academy grad if the rabbits are indeed called yard cats, and she replied, “If not they should be!”
The Smithsonian’s National Museum of Natural History has a Pinterest page for Squirrel Week, although I can’t tell when the page dates from; they also have an authoritative guide to all 80+ species of North American squirrels. For Squirrel Week 2013, Kelly interviewed the Smithsonian’s Richard Thorington, who gave him a tour of the “Squirrel Range” at the USNM. I tried to embed the video, but failed. JAC: click on the screenshot below to go to this biologically informative tour of squirrels:
I was able to embed one of the 2013 Squirrel Week videos, in which the video reporter interviews John Kelly.
When I posted about Daniel Matute giving the Dobzhansky Lecture at the evolution meetings, one of the commenters asked if his talk was recorded so it could be viewed online. At the time I didn’t know– I knew some talks were recorded, but I didn’t know which ones. Well, the recordings which were made have now been posted at a dedicated Youtube channel, Evolution 2014. Daniel’s, alas, is not among them. Since we all like squirrels though, here’s one on squirrels, “A history of high latitude adaptation in Holarctic ground squirrels (Urocitellus)”, by Bryan McLean from the Museum of Southwestern Biology at the University of New Mexico.
Recording talks for posting online was an experiment at this year’s meeting, and about 80 are available. You can usually see the slides well, the speaker not so much; the audio is soft, but audible on the ones I checked. You can browse the Youtube channel linked to above, or look at a list of the talks in a searchable spreadsheet format here. The number recorded may increase at future meetings.
Here’s one more talk, on “The tangled evolutionary histories of Madagascar’s small mammals”, by Katie Everson, from the University of Alaska Museum. This talk I saw “live” at the meeting– island evolution is just about my favorite topic.
