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.
Although Jerry has been receiving fresh wildlife photos from readers, I thought I’d chip in with a few of mine and my correspondents from San Diego. We begin with a wild inhabitant of the San Diego Zoo, the introduced green anole, Anolis carolinensis. Native to the southeastern United States, they became established at the Zoo many years ago, probably by escapees.
Anolis carolinensis, female, in West Indian rock iguana exhibit at San Diego Zoo, September 1, 2018.
They are now scattered through several southern California counties, although it’s not clear if they are established and reproducing in all locations from which they have been reported. Another anole, the brown anole, Anolis sagrei, is also in southern California. Greg Pauly, of the LA County Museum, is studying these very interesting introductions. Much can be learned about ecological and evolutionary processes from study of populations confronted by, and confronting, new biotic and physical environments for the first time.
Next we have a western fence lizard, Sceloporus occidentalis, a native species, from Point Loma, San Diego.
Sceloporus occidentalis, Point Loma, San Diego, California, March 22, 2019.
Old Point Loma Lighthouse, San Diego, March 22, 2019.
We’ll finish off with two inhabitants of Murphy Canyon, a suburban neighborhood within the city of San Diego. First a snail on the sidewalk– I’ve no clue on the ID.
Snail, Murphy Canyon, San Diego, March 22, 2019.
And last, but certainly not least– in fact I think it’s the best in this set– a southern alligator lizard, Elgaria multicarinata. It was just strolling along through a lawn.
Southern alligator lizard (Elgaria multicarinata), Murphy Canyon, San Diego, California, March 15, 2019.
On my recent visit to San Diego, I got to see one of my favorite ducks, a merganser. Mergansers are fish-eating diving ducks. Here’s a Red-breasted Merganser(Mergus serrator), diving in San Diego Bay, viewed from the Coronado Aquatics Center, on the Coronado Strand.
Mergansers have bills adapted to catch their prey, which are quite different from those of other ducks or, indeed, birds in general. Instead of the broad, flattened bill typical of ducks (the origin of the term ‘duckbilled’), their bills are long and narrow. And, though all modern birdslack teeth, there are a series of tooth-like serrations on the bills of mergansers which help them grab fish, frogs, and the like.
Skulls of a mallard (Anas platyrhynchos), top, and a merganser, bottom.
There are some geese that have similar structures on their bills, but they are more like transverse grooves rather than serrations. Geese are typical Anseriformes (the order to which ducks, geese, and swans belong) in their feeding habits, and do not catch fish; it is interesting that the only birds I know of with these approximations to teeth are in that order.
Close up of the bill of a merganser, showing tooth-like serrations.
(The merganser skull shown above is probably one of the two species found in Wisconsin, either the Hooded Merganser [Lophodytes cucullatus; resident breeder in SE Wisconsin] or the Common Merganser [Mergus merganser; breeds from northern Wisconsin up through the taiga belt of Canada and Alaska, but winters in SE Wisconsin].)
I also saw a Surf Scoter (Melanitta perspicillata), another diving duck, also at the Aquatics Center. The body of water here is Glorietta Bay, a part of San Diego Bay enclosed by Coronado “Island”, the Strand which connects Coronado “Island” to the mainland (the reason Coronado “Island” is not an island), and a landfill extending from the Strand on which a Navy base is located. The scoters have broad bills, but they’re higher in the back (unlike mallards), and they feed on mollusks.
The bird in the video above is a male, as you can tell from the white markings on its head and neck. I saw several more Surf Scoters while sailing in San Diego Bay off National City, flying just above the water in small groups, but unfortunately did not get any photos. Both of these species of duck breed mostly on fresh water in the taiga and high arctic, and winter along the sea coasts, so it was a rare opportunity for me to see them.
Mallards (Anas platyrhynchos), Balboa Park, San Diego, California, January 16 2019; note the female sleeping on shore amongst the flowers.
I have often noted an excess of males when observing Mallards (often two males with a single female), as in the photo above, but I don’t know why that’s the case; a pair walked about near the pond.
Mallards (Anas platyrhynchos), Balboa Park, San Diego, California, January 16 2019.
As Cornell’s All About Birds reminds us, not everything that floats is a duck, and on a later visit to Balboa Park, I photographed this American Coot (Fulica americana). There were also more Mallards about that day—I counted 22 at the Pond.
American Coot (Fulica americana), Balboa Park, San Diego, California, January 18, 2019.
The coot later went ashore and fell asleep. In looking at photos of the Mallards from my first visit, I noticed a coot in the background on the pond (first photo above)– probably the same individual. (You can find out more about the birds of Balboa Park at the Birds of Balboa Park page.)
American Coot (Fulica americana), Balboa Park, San Diego, California, January 18, 2019.
The Lilly Pond did have a few lily pads.
Lily pads, Balboa Park, San Diego, California , January 18, 2019.
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
