Today marked the first day of the 2018 Henslow's Sparrow surveys at Big Oaks NWR. Each year, Big Oaks does 2 rounds of surveys for the Henslow's Sparrow. Each day of the survey, we must be at the site by 6 am, where we listen for the Henslow's Sparrow's call, and mark how many we hear and how far away they are from us.
The Henslow's Sparrow is a state-endangered species. It breeds in the Midwest and North Eastern regions, and winters in the South and South Eastern regions. The grasslands of the Midwest makes up the breeding habitat of the Henslow's. Big Oaks NWR has one of the largest breeding populations of Henslow's Sparrows. Because of the intense agriculture, most habitat in Indiana is not suitable for the Henslow's Sparrow, but Big Oaks has some of the largest sections of grasslands in Indiana.
It was determined that regular disturbance of grasslands, in the form of prescribed burns, has contributed to the population increase of the Henslow's Sparrow. The summer immediately following a burn of a grassland area, will have no Henslow's Sparrows present. This is due to the fact that Henslow's Sparrows prefer undisturbed, tall, dense grasslands. Three seasons after a burn showed the highest abundance of Henslow's Sparrows present in a grassland area. This data is consistent with the data from our surveys, thus far. In the areas which were burned earlier this year we did not hear the song of the Henslow's Sparrows, while in the grasslands burned in previous years we heard a medium-high abundance of the songs of Henslow's Sparrows.
Big Oaks has been conducting Henslow's Sparrow surveys since 1995. And since they have started conducting the surveys, Big Oaks has been making large strides in the effort to improve the Henslow's Sparrow population in Indiana. Indiana has little forested areas, due to the high volume of agriculture in the state. One may wonder, since Henslow's Sparrows prefer grasslands, that crop fields could provide the same needs to the Henslow's. However, with the frequent disturbance (multiple times during the year, plus in the middle of the summer when Henslow's Sparrows are nesting), crop fields provide no benefit. Making Big Oaks NWR a true refuge for the Henslow's Sparrow, providing large areas of grasslands.
I encourage any birder, no matter your skill level, to take a visit to Big Oaks NWR to hear the song of the Henslow's Sparrow. To make sure you hear the Henslow's Sparrow, schedule a bird tour with Big Oaks. Bird tours allow you to visit areas of the refuge, other than the public use area, where you will undoubtedly be able to hear the sweet song of the Henslow's Sparrow.
Herkert, J.R. 1994. Status and Habitat Selection of the Henslow's Sparrow in Illinois. The Wilson Bulletin, 106 (1), 35-45.
Cooper, T.R. (Plan Coordinator). 2012. Status Assessment and Conservation Plan for the Henslow's Sparrow (Ammodramus henslowii). Version 1.0. U.S. Fish and Wildlife Service, Bloomington, Minnesota. 126pp.
The Cornell Lab of Ornithology. (2017). Henslow's Sparrow. All About Birds. Retrieved from https://www.allaboutbirds.org/guide/Henslows_Sparrow/overview