Northern Prairie Wildlife Research Center
It's 5:53 am. The sun is barely over the horizon, as we begin walking waist-deep in a dense stand of alfalfa and wheatgrass in Eddy County, North Dakota. Separated by about 400 yards, we slowly traverse the field along parallel transects. Heavy dew covers the vegetation, sparkling like diamonds in the early morning sun. The air is calm, and the temperature is scarcely above 50 °F. A few scattered insects call from the vegetation, announcing the end of another night and the beginning of a new day.
In the distance, chorus frogs emphatically call from a nearby wetland. The sky is mostly clear this morning, except for a few wispy clouds that blanket the rising sun in hues of blues, pinks, oranges, and yellows.
As we journey across the field, Le Conte's Sparrows jump up in front of us and then dive quickly into the vegetation a few yards away, never to be seen again. Throughout the field, we can hear numerous male Le Conte's Sparrows singing from within the vegetation. We treasure mornings like this: cool temperatures, a clear sky, no wind, and lots of Le Conte's Sparrows.
Our assignment is to count breeding birds in grassland fields enrolled in the Conservation Reserve Program (CRP). Since 1990, we have been surveying breeding birds in over 400 fields in nine counties in North Dakota, South Dakota, Minnesota, and Montana. Many of these fields have been visited every year. A long-term and broad-scale study of this magnitude would not be possible without the support and cooperation of private landowners; for this, we are extremely appreciative.
CRP has been a boon for nesting waterfowl during the last decade. The values of the CRP to other birds, such as the Le Conte's Sparrow, are less well known, but data from this and other studies indicate that many other birds have benefitted from CRP as well. The Le Conte's Sparrow is just one of over 100 species of birds that we have observed between 1990 and 1998 using these CRP fields during the breeding season. Some species of birds are fairly common in CRP fields, including the Grasshopper Sparrow, Savannah Sparrow, Clay-colored Sparrow, and Bobolink. Others are found only in low numbers in CRP fields in this region, such as the Henslow's Sparrow, the Nelson's Sharp-tailed Sparrow, and Brewer's Sparrow. And some, such as the Le Conte's Sparrow, are abundant in some years and rare or absent in others.
The Le Conte's Sparrow is arguably among the most poorly known of North America's grassland birds. The species is one of several sparrows belonging to the genus Ammodramus. Ammodramus sparrows occur primarily in grasslands and wetlands in North America, and are notorious for their cryptic plumage and secretive behaviors. The Le Conte's Sparrow is no exception. During the breeding season, the Le Conte's Sparrow is extremely secretive, skulking about and diving into vegetation with unbelievable agility. Both adults and juveniles often escape attention by running along the ground in dense cover rather than flying. This elusive behavior has been described as mouse-like by some and as frustrating by others, especially those interested in catching a glimpse of a bird. The species' cryptic plumage is more colorful than most grassland sparrows, and the species is considered by many to be one of the most attractive sparrows in North America.
Only the male Le Conte's Sparrow sings, often from a concealed location within dense vegetation. Their song is weak and short, resembling an insect more than a bird. The song is barely audible over the similar calls of the crickets, grasshoppers, and other sounds of the grasslands. Ernest Thompson Seton, a renowned naturalist and artist, described the Le Conte's Sparrow song as "so thin a sound, and so creaky, that I believe it is usually attributed to a grasshopper." Thomas Roberts, a well-known Minnesota ornithologist, described the species' song as an "amusingly squeaky little ditty." Although Le Conte's Sparrows sing throughout the day, they tend to sing more often in the evening and at night.
During the breeding season, the Le Conte's Sparrow generally prefers moist grassland and wet meadow habitats. The species tends to avoid areas with woody vegetation or permanent standing water, although they often are found along the peripheries of wetlands. This affinity for moist habitats has resulted in the species being known more as a wetland bird or wet meadow species than as a grassland bird. This confusion probably reflects the similarity in grassland-like vegetation that is characteristic of both wetlands and grasslands within the species' breeding range.
Habitat preferences also likely explain the species' use of CRP grasslands in our study. The perennial grassland habitats established by the Conservation Reserve Program are similar to other upland habitats -- such as prairie and hayland -- used by the Le Conte's Sparrow elsewhere in its breeding range. Although vegetation varies considerably among CRP fields, most CRP land in the northern Great Plains was planted to a mixture of legumes and grasses.
Le Conte's Sparrows were nearly absent from CRP fields that we surveyed between 1990 and 1993. In 1994, however, Le Conte's Sparrow populations experienced a dramatic increase in the region. This increase continued in subsequent years, and by 1996 the Le Conte's Sparrow was one of the most common breeding birds in the CRP fields that we surveyed. The species was most common in 1994 to 1997 in Eddy and Kidder counties in North Dakota, which lie within the species' usual breeding range. The species also increased in counties on the southern edge of its breeding range (Day County in South Dakota, Grant County in Minnesota, and Sheridan County in Montana), as well as in counties that are outside of the species' normal breeding range (Hettinger County in North Dakota and McPherson and Butte counties in South Dakota). By 1997, Fallon County, Montana was the only one of nine surveyed counties in which Le Conte's Sparrows were not found.
Why did Le Conte's Sparrow populations increase so dramatically? Given what we know about the Le Conte's Sparrow's preference for moist grassland habitats, we suspect that climatic variability in the region may have been a major factor leading to these dramatic fluctuations in Le Conte's Sparrow abundance and distribution. The climate of the northern Great Plains is highly dynamic, with great annual variation in precipitation and periodic, often extreme, wet and dry cycles. In particular, drought is a major force of disturbance on the Great Plains, and has been an important influence in directing the evolution of grassland plants and animals in this region.
|Species Profile: Le Conte's Sparrow (Ammodramus leconteii)
Size: One of North America's smallest sparrows; five inches.
Plumage: Streaked back and sides, yellow-brown throat and underparts with reddish brown collar, white stripe through dark crown, bright orange stripe over each eye, and a bristly sharp tail. Sexes outwardly similar.
Habitat: Frequents moist grasslands, wet meadows, peripheries of wetlands, hayland, retired cropland, and native prairie; avoids areas with permanent standing water.
Food: In summer, eats primarily insects and spiders, in winter, forages on forb and grass seeds.
Similar species: On the breeding grounds, the Le Conte's sparrow may be confused with Nelson's sharp-tailed sparrow, grasshopper sparrow, and Baird's sparrow, all of which may frequent similar habitats.
Song: An insect-like buzz or Tzeek-tzzzzzzz-tick; male alone sings, usually from concealed location within vegetation; occasionally sings while flying.
Nest: Well concealed, cup-shape nest placed on or near the ground in a clump of grass; female alone builds the nest; the brown-headed cowbird,a brood parasite, occasionally lays egg(s) in their nest.
Eggs: 3-5 eggs (usually four); grayish-white eggs with brown spots; 11-13 days incubation; female alone incubates eggs.
Breeding season: Peak breeding period is late May to mid-July.
Breeding distribution: Central and southern Canada and extreme north-central United States.
Migration: Arrives in northern Great Plains in early April; departs for wintering grounds in late summer or early autumn.
Winter Distribution: Winters primarily in the southern United States.
Figure 2: Distribution of Le Conte's Sparrow
Our study has encompassed some of the driest as well as the wettest growing seasons on record in the northern Great Plains. Between 1987 and mid 1993, drought conditions prevailed over much of the study area. Conversely, between mid 1993 and 1997, the region experienced some of the wettest conditions on record. The dramatic increases in Le Conte's Sparrow numbers coincided with the occurrence of the extreme wet conditions in the region, and changes in Le Conte's Sparrow densities generally paralleled changes in moisture conditions. The species' response to increased moisture in the regions was not immediate, but rather lagged behind by one or more years. This lag in response to increased moisture was noted in all counties, but was most apparent in Kidder County, North Dakota. Although grassland vegetation responds relatively quickly to changes in weather compared to woody vegetation, conversion of these changes in moisture into variations in bird abundance often lags behind.
In his book, Breeding Birds of North Dakota, Robert Stewart alluded to these dramatic fluctuations in Le Conte's Sparrow populations, stating that the Le Conte's Sparrow "reaches peak numbers during wet years, while during dry years it may be scarce or absent." There also is evidence to suggest that Le Conte's Sparrows respond similarly to moisture during migration and on their wintering grounds by shifting their distribution and abundance. Dramatic changes in breeding bird distribution and abundance of this nature also have been documented for other grassland and wetland birds that breed in the northern Great Plains, including Lark Bunting, Dickcissel, Baird's Sparrow, Grasshopper Sparrow, and many waterfowl species.
It is now 6:29 am. As we continue our bird survey across the CRP field in Eddy County, we can't help marveling at the splendor of bird life in this region during the summer months. Our thoughts are interrupted by a male Western Meadowlark alighting on a nearby fencepost to sing its cheerful and bubbly song. Several more meadowlarks can be heard in the field and the surrounding landscape.
Other grassland birds join the morning chorus. Clay-colored Sparrows sing insistently from a patch of dead vegetation. A pair of Upland Sandpipers circles overhead, heralding their presence with an occasional high-pitched wolf-whistle. A male Bobolink chases a male Red-winged Blackbird from its territory, only to return a few seconds later to its mate, which is perched on a barbed-wire fence. A pair of Grasshopper Sparrows flits about, scolding us repeatedly with their sharp chip notes. A couple of steps later, a female Mallard bursts from the undergrowth, revealing a nest with eleven eggs surrounded by a ring of downy feathers.
And throughout the field, we hear Le Conte's Sparrows passionately singing their insect-like song, declaring their presence to whoever will listen. Tzeek-tzzzzzzz-tick. Tzeek-tzzzzzzz-tick. We can't help wondering if the Le Conte's Sparrow will be in this CRP field next year or the year after that. Regardless, we will enjoy the species while it is here, for the species is truly an ephemeral jewel of the northern Great Plains.