Situated in the open landscape of Iowa’s Prairie Pothole Region, South Twin Lake (Figure 1) serves as a magnet for waterfowl and other migratory birds. In fact, due to significant duck and goose numbers documented here in recent years, this glacial lake (and its associated marshes and woods) was recently added to the state’s list of Important Bird Areas. Diverse gatherings of birds are almost always found on the water here during spring and fall, and the peak seasonal concentrations of various ducks can be quite impressive at times. South Twin also provides refuge to land-bird migrants along its periphery, giving birders a variety of options during a visit.
Figure 1. Birding South Twin Lake in Calhoun County: (1) Twin Lakes Road, (2 and 3) boat ramps and clearings, (4) gravel pull-off.
There are multiple lakeside access points off of Twin Lakes Road (Figure 1.1), which itself follows closely along much of the lake’s perimeter. Along the wooded northeastern shore (just across from Twin Lakes Golf Course), roadside pull-offs enable views of the marshy portion of the lake. Many geese, including Greater White-fronted, Ross’s, Snow, and Cackling, often congregate along the cattails throughout this section in both spring and fall. Most of the expected dabbling ducks are usually found here as well, making this a prime spot to look for Cinnamon Teal among the many Blue-winged Teal and Northern Shovelers. However, even if there aren’t any rarities to be found on a given day, taking some time to tally and observe the interesting behaviors of the assorted waterbirds here definitely makes the stop worthwhile.
At the south end of the lake, small boat ramps and clearings (Figures 1.2 and 1.3) enable visitors to scan the lake in its entirety, and to discover any birds that were blocked by vegetation during initial searches. Although each spot is worth at least a quick check, the westernmost of these southern accesses is typically the best place to commence searches for diving ducks, loons, and grebes out on the broader portion of the lake. Although Pied-billed Grebe and Horned Grebe are most likely to be seen, all six of Iowa’s grebe species have been recorded at South Twin. With more consistent searching, the rarer loons may be added to the site list as well. Sea ducks like Surf, White-winged, and Black Scoters, and Long-tailed Duck are probably annual visitors here. Patiently searching through large rafts of divers in the fall is one key to finding scoters and long-taileds, although you can readily find them individually or in monospecific groups, too.
The south side of the lake is also the foremost place to observe gulls that are either in flight or resting on the lake itself. During many of my fall visits to South Twin, most of the gulls are absent mid-day but gradually return to the water during the evening. Franklin’s Gull, one of the signature species of prairie-lakes landscapes, visits South Twin in migration and gathers in substantial numbers in late September and early October. Iowa has an impressive list of gull species overall, and sorting through flocks of the more widespread species (e.g., Ring-billed Gull) increases your chances of finding a more unusual visitor.
In fall, it is also useful to scope agricultural fields off the south end of the lake, as they frequently have foraging/resting flocks of geese. This provides a means of watching these birds without the disruptive heat shimmer seen over bodies of water under certain conditions.
Heading around the west side of the lake, you’ll eventually come to a wide gravel pull-off at the north end (Figure 1.4). This overlook––situated next to a steep, cliff-like segment of shoreline––is a great place to investigate the northern half of South Twin during the afternoon and evening. With the sun at your back, you can serenely scan all of the aforementioned marshy habitats that extend to the opposite shore. Checking the vicinity of these marshes is also the best way to detect herons, night-herons, egrets, bitterns, and other shallow-water denizens. Shorebirds also frequent this area when there are at least a few mudflats exposed along the edges.
The narrow belt of trees and shrubs around South Twin’s shoreline attracts woodland/edge migrants in season. Walking or slowing driving along Twin Lakes Road can sometimes produce a surprising list of Neotropical songbirds, particularly under fallout conditions (i.e., the arrival of cold fronts in the fall and strong storm systems in the spring). Kinglets, thrushes, warblers, etc. are relatively easy to pick out as you move through this restricted habitat, which is a one-of-a-kind sanctuary for miles in each direction. Of course, when scoping the lake for waterfowl, it isn’t unusual to become pleasantly sidetracked by the songbird activities happening around you.
These lightly wooded and brushy habitats regularly hold Emberizids (native sparrows), too. I usually pause for a few minutes to monitor the roadside songbird activities before setting up my scope for waterfowl viewing. Although the northeastern shoreline is the most productive in this regard, opportunities for native-sparrow observations exist all the way around the lake.
Back at the northwest corner, a small wildlife area (just across from the overlook) provides another concentrated habitat for migrant songbirds. When conditions are right, this is a great location to obtain direct, eye-level looks at Harris’s, White-crowned, Fox, Swamp, Song, Lincoln’s, and American Tree Sparrows, especially in October. The adjacent crop fields offer a handy opportunity to scan for open-country species like Horned Lark, American Pipit, Vesper Sparrow, Savannah Sparrow, Lapland Longspur, and perhaps Smith’s Longspur during migration.
Back across the road at the north end of the lake, the marshes and woods teem with vociferous assemblages of blackbirds, which routinely number in the thousands. Such flocks usually have a few Rusty Blackbirds in their midst in March, April, and October. Brewer’s Blackbirds, which are much less likely to join the big mixed-species congregations, have been noted in the vicinity of the overlook, and probably take advantage of the nearby plowed fields and feedlots. For sure, birding along the edge of the road can allow you to see many species with minimal effort. Furthermore, since this little viewing location is right next to the overlook, you can bolster your day list without adding many miles to your trip.
Many of Iowa’s raptor species make appearances at South Twin during migration. Northern Harriers are customarily seen coursing over nearby fields and prairie patches. Merlin, Peregrine Falcon, Cooper’s Hawk, and Sharp-shinned Hawk are occasionally spotted in flight near the lake or perched in trees along it. Additionally, the South Twin vicinity can produce all of the various western Red-tailed Hawk types (dark-morph, rufous-morph, Krider’s, Harlan’s, etc.) that venture into the state.
Goose and duck hunters frequent South Twin Lake, and pheasant hunters sometimes explore the adjoining fields. Therefore, like at many wildlife areas in Iowa, wearing at least some blaze-orange clothing during the corresponding hunting seasons is advisable. But again, much of the birding here is easily accomplished from the roadside, and there’s plenty of room for everyone to accomplish their outdoor hobbies.)