I toyed with different versions of this awkward blog entry title, but really it ties into my previous post, “Where are the nighthawks now?”
As we saw in that post, birds can cover a lot of ground in a year. Each of these places has to be habitat-friendly for a migrating bird. Here in South Dakota, birds encounter a number of biome types, called ecoregions.
I study Common Nighthawks in 47d, 46n, 42f and 47a.
47d – Missouri Alluvial Plain – Elevation 1100 – 1200 ft.
The human development of the Missouri Alluvial Plain over the last two centuries has separated the Missouri River from its floodplain. A system of dams, levees, and stream channelization has largely controlled the flood cycles to allow intensive agriculture in the river bottomland. Much of the northern floodplain forest has been cut, and oxbow lakes and wetlands have been drained to reclaim additional agricultural land.
46n – James River Lowland – Elevation 1200 – 1850 ft.
The boundary between the James River Lowland and the Drift Plains (46i) to the north represents a broad phenological and climatic transition zone. This ecoregion is characterized by mesic soils, warmer temperatures, and a longer growing season than the Drift Plains (46i). These differences are reflected in the crop types of the region. Winter wheat, corn, and soybeans are more prevalent in this ecoregion’s milder climate.
42f – Southern Missouri Coteau Slope – Elevation 1400 – 2200 ft.
The Southern Missouri Coteau Slope differs from the Missouri Coteau Slope (42c) to the north; it has mesic soils rather than frigid soils and a substantial cap of rock-free loess. To the south, the coteau areas east of the Coteau Slope ecoregions (42c, 42f) become progressively narrower and more eroded. The level to rolling uplands of the Southern Missouri Coteau Slope are planted in sunflowers, wheat, millet, and barley. Corn is a marginal crop that does well in wet years. The stream drainages tend to be grazed. Willows, green ash, and elm grow in the riparian areas.
47a – Loess Prairies – Elevation 1200 – 1700 ft.
The Loess Prairies of Iowa and South Dakota surround the perimeter of the Des Moines lobe of the Late Wisconsinan glaciation. Of the two areas in South Dakota, the northern one is distinguished from neighboring regions by its rock-free soil and a paucity of wetlands. The southern area is more highly dissected, with deciduous woodland and brush on the steeper slopes and in the draws.
(Source: sdakotabirds.com, EPA)
These four ecoregions even within southeastern South Dakota vary quite a bit, and so do Common Nighthawk abundances. The change in landscape and nighthawk abundance are even more marked when you move further west into the Badlands, western grasslands, and the Black Hills where row crop dominance drops away.
Common Nighthawks need gravel rooftops or gravelly parts of grassland and rangelands with shortgrass prairie or heavily grazed tallgrass. Or, they can thrive in open forests, like those of the Black Hills. Below is a map for all years, all months for the ebird Common Nighthawks sightings in South Dakota. You can see a concentration of nighthawks in the west in the Black Hills and Badlands and in urban areas like Vermillion and Sioux Falls. Of course, these sightings have some bias as to where observers tend to be.
Common Nighthawk sightings in South Dakota (source: ebird)
Migrating flocks can show up anywhere because they don’t need gravel areas for camouflaging eggs. My first sighting of nighthawks in South Dakota was in September, 2011, the year before I moved here. It was an unlikely spot to see them. There was a a group of 100 flying over row crop along I-90. Of course, migrating nighthawks have the benefit of covering a lot of ground in a day and can forage while flying. Their needs are more simple than a migrant seed eater that needs a forest, as my lab mate Dr. Ming Liu found
It’s also important for researchers to understand habitat use in the other areas of a bird’s yearly migration. Cornell Lab of Ornithology’s Golondrinas de las Americas foundation and other organizations supply grants to researchers in South America and Central America. Last year’s North America Ornithological Conference featured symposia of South America and Central America research.
Newer technologies are helping researchers throughout an organism’s range with more expansive data. Satellite tags, like those developed for the Argos system, are becoming smaller and lighter which enables research of larger array of species. These data can be downloaded without recapturing the bird, which is crucial for wily birds like Common Nighthawks.
Behold, the future!
Ecoregion summaries from “Ecoregions of North and South Dakota”, U.S. EPA published map. Primary authors: Sandra A. Bryce (Dynamac Corporation), James M. Omernik (USEPA), David E. Pater (Dynamac Corporation), Michael Ulmer (USDA), Jerome Schaar (NRCS), Jerry Freeouf (USFS), Rex Johnson (SDSU), Pat Kuck (DENR/NRCS Liason), and Sandra Azevedo (OAO Corporation).