(1) 1922B North Center St. Rd., Marshalltown, IA 50158.
(2) Iowa Cooperative Fish and Wildlife Research Unit, Science Hall II, Iowa State University, Ames, IA 50011.
Published in Iowa Bird Life 66:117-122 (1996)
Introduction | Study Area/Methods | Results | Discussion | Literature Cited
The loss of native habitat and consequently native birds to agriculture was noted by DuMont (1931) in Polk County and by Tinker (1914) in Clay and Palo Alto counties, presumably reflecting trends in the rest of Iowa. DuMont (1933) considered the species a "fairly rare migrant" and noted "...the seeming disappearance of the Henslow's Sparrow. There have been no breeding records in a number of years." (DuMont 1933:10). L.J Bennett (in Hyde 1939:13) attributed this scarcity of records to the lack of observers and noted Henslow's in northwestern Iowa throughout the 1932-37 breeding seasons. The species was still found on Kalsow Prairie in Pocahontas County (Youngworth 1953) and Hayden Prairie in Howard County (Ennis 1959) in the 1950s. Recently, only two Iowa sites, Hayden Prairie (Kent and Bendorf 1984) and the Lake Sugema area in Van Buren County (Dinsmore 1987), have provided observers with reliable annual sightings.
Henslow's Sparrow was listed nationally as a Species of Management Concern in 1987 and 1995 by the U.S. Fish and Wildlife Service (USFWS 1995). The purpose of this paper is to aid observers in locating the species by reporting observations of the birds' habits and the habitat in which they have been found. By using this information, birders may increase the number of sightings and identify new areas occupied by Henslow's Sparrow, contributing to our limited knowledge of the species. We also document the two nests we found.
The Lake Sugema nest was found in the northwestern part of the wildlife area, in a field of mostly smooth brome grass interspersed with goldenrod, wild parsnip and common milkweed, outlined by trees in the fencerows. As one of us (PM) was walking through the field, a sparrow with dark brown markings on its wings and back flushed directly from the nest. The bird flew about 8 meters (m) before dropping to the vegetation. There was no distraction display, such as one often observes in Grasshopper Sparrows (Ehrlich et al. 1988; PM, pers. obs.). The cup-shaped nest was well concealed in dense, smooth brome grass 38 centimeters (cm) in height with heavy litter around and over it. Constructed of fine grasses and woven into several grass stems, the nest faced southwest with the rim at a 30 degree angle. The bottom of the nest was about 5 cm above the ground. The nest contained five eggs, which were off-white and distinctly wreathed with reddish-brown markings at the large end. Chip notes, a thin tsip, came repeatedly from the vegetation, but no bird was seen. The chip note was consistent with that given by Henslow's Sparrow and was different from that made by Grasshopper Sparrows. Henslow's had been singing in the field, but no Grasshopper Sparrow songs had been heard.
Two additional visits were made to the nest (by PM). On 9 July an adult sparrow flushed about 6 m from the nest. The four or five young had closed eyes, red gape, a yellow spot on the end of each tongue flange, light grey down, and feather bundles in tracts. A Henslow's sang once nearby, but was not seen. On 15 July an adult flushed 6 m from the nest when approached (by PM) and chipped three times. There were at least three young, which had their eyes open and were fully feathered except for the crown which still had some down. After a few minutes, the chipping sounds of a bird were heard repeatedly from nearby. After 10 minutes, an adult Henslow's appeared on a fallen milkweed plant with a green caterpillar in its bill. The bird was observed for 30 seconds before it disappeared into the vegetation. After leaving the nest site, the observer could still hear chipping coming from the area.
On each of the two later visits, the vegetation appeared more disturbed than previously, so that an opening was created which allowed a clear view of the nest and young. It is unclear whether this progressive opening was caused by nestling activity or the adults' feeding visits, but it presumably increased the risk from avian predation. The disturbance did not result from observer activity.
The Eldon Wildlife Area nest was found (by PM) in a field dominated by very clumpy orchard grass, approximately 20 percent forbs (goldenrod and wild parsnip) with some bare ground between the clumps. A small sparrow flushed underfoot, then flew about 10 m before dropping to the vegetation without giving a distraction display. The cup-shaped nest was on the north side of an orchard grass clump adjacent to several goldenrod stems. Concealed under a canopy of live grass and litter, the nest was woven of fine grass, about 7 cm off the ground, and level. The four eggs were off-white with reddish-brown spotting and wreathing at the large end. After a few minutes, a nearby Henslow's began to sing loudly and was joined in singing by a second Henslow's. On a later visit, the nest could not be relocated.
Other investigators have found the nests of Henslow's Sparrow to be a deep or open cup placed in or near the base of a clump of grass (Wiens 1969), the bottom 5 cm to 7.6 cm (2-3 in.) off the ground, with dead grass forming an arched roof (Hyde 1939, Skinner et al. 1984). Habitat requirements are reported to be tall, dense vegetation (Herkert 1994b), tall, dense grass with scattered, tall forbs (Skinner et al. 1984), and residual dead vegetation (Herkert 1994a,b; Wiens 1969; Zimmerman 1988). Hyde (1939) found the majority bred in grassy meadows, usually bush-dotted, and dominated by hummocks of cord grass. Others used shrub-sprinkled, grassy uplands.
Although the species was undoubtedly a native breeder, historical records of Iowa Henslow's Sparrow nests are difficult to document and lack useful descriptions. Anderson (1907:317) listed a nest found in Grundy County and credited to Bingaman "one nest found and female shot in 1899". Lynds Jones (Davie 1900:372) described the habitat, nest, and eggs of the Henslow's in Iowa, which would have required actual observations. Bent (1968:788) cited nine Iowa records for "egg dates" from 18 May to 29 June, which also suggests nest observations. An adult bird was seen with a green caterpillar in its bill on Kalsow Prairie before disappearing into the grass (Youngworth 1953). Without other recent records, the nests in Van Buren and Davis counties nests reestablish Henslow's Sparrow as a breeding resident in Iowa.
Several populations of the species were found in 1996 throughout the study area. On a landscape level, the occupied fields tended to be in areas of one to several sections dominated by pasture, uncut grass hay, and CRP fields. The fields of suitable habitat were 40 to 160 acres. Typical fields have smooth brome grass 45 cm to 85 cm (18 to 30 inches) in height, about 5% to 20% of the area in forbs, and dense, standing litter (the previous years' dead grass stems and leaves). The general impression of one of us (PM) was that in mid-June to late July the fields that supported Henslow's appeared half brown and half green.
Henslow's are more difficult to detect than most other grassland species, sometimes singing inconsistently and often from within the canopy. The presence of Grasshopper Sparrows and Sedge Wrens in the same field may indicate that an observer is in Henslow's habitat. We found the three species together frequently in our study fields. In Michigan, Hyde (1939) found the species most commonly associated with Henslow's Sparrow to be Sedge Wrens, a species that prefers tall, dense vegetation, and Savannah Sparrows, a species with habitat preferences similar to Grasshopper Sparrows. Walking slowly through the habitat may stimulate silent birds to sing (PM, pers. obs.). Hyde (1939) noted that singing seemed to be the species' response to disturbance near the nest. Zimmerman (1988) found the use of taped playbacks effective for locating males. In our study fields, taped playbacks elicited a response from only one male (when his own song was played back), although it was an immediate and aggresive response. Fields that appear to be suitable habitat may require repeated visitation to locate uncooperative birds.
Simply protecting fields where Henslow's occur is not enough to maintain the population. Active grassland management is necessary to maintain suitable habitat for Henslow's and other grassland species (Herkert 1994a, Smith and Smith 1992). Without disturbance (i.e., management), upland grasslands will be invaded and eventually replaced by woody growth, excluding Henslow's from using the habitat. Currently, three management techniques are generally used to prevent woody invasion: Spring burning, mowing, and grazing (Herkert 1994a,b; Skinner et al. 1984; Smith and Smith 1992; Zimmerman 1988). On southwest Missouri prairies, unintensive haying (every 1-3 years) has been shown to maintain consistent Henslow's numbers (Swengel 1996) while achieving management goals. While these practices tend to reduce the amount of habitat available for Henslow's for one or two seasons, the habitat needs of other species (Bobolinks, Grasshopper Sparrows, Horned Larks, Upland Sandpipers, etc.) are met during this time. By using a rotational system that incorporates any of the above practices, the grassland successional stage can be maintained and essential habitat provided for many grassland species (Herkert 1994a; Swengel 1996; Zimmerman 1988).
The discovery of breeding birds in the state is encouraging news for Henslow's Sparrow, but it is only a first step toward ensuring the species' continued presence in Iowa. It is still necessary to identify new populations, quantify their habitat needs, and explore ways of managing for this species and other grassland birds. By using science and education we can improve the odds that Henslow's Sparrow will continue to breed in Iowa.
We thank James P. Sandrock for showing us the locations of birds in the Lake Sugema area and David J. Horn for comments on this paper.
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