1. Heterospecific Attraction in Grassland Birds: Who’s Listening to Whom
John E. Andrews, Jeffrey D. Brawn and Michael P. Ward
Abstract
Several studies have investigated conspecific attraction among grassland birds, however, the effects these experiments have on non-target heterospecifics is unknown. Heterospecific information may be a valuable resource when selecting breeding habitat since grasslands can change from year to year. We conducted conspecfic and heterospecific experiments in conservation grasslands throughout Central Illinois, USA. We found stronger evidence for conspecific information use than heterospecific during breeding seasons. Understanding heterospecific information use in grasslands has implications for finer scale habitat selection as well as broad scale distributions in birds. Mapping the information landscape in grassland birds and how habitat selection is affected could illuminate new solutions to grassland bird declines in the Midwest.
Results
In 2010 & 2011, Grasshopper Sparrow playbacks elicited significantly higher densities in conspecifics (F1, 26=6.78, p=0.015, N=32) and trends toward higher densities in Eastern Meadowlark’s as a heterospecific response.
In 2012, Eastern Meadowlark’s and Red-winged Blackbirds (Agelaius phoeniceus) seem to respond to Meadowlark playbacks (EAME-T). Vesper Sparrows (Pooecetes gramineus) appear to respond equally to Meadowlark and Blackbird playbacks more than silent controls and Grasshopper Sparrows seem to avoid each of these treatments (Figure 4).
Figure 5: Map of State Acres for Wildlife Enhancement (SAFE) sites throughout Illinois. Red polygons show sites where enrollment is available to private landowners. All study sites were located in four locations throughout central Illinois indicated by blue circles.
GRSP-PB
EAME-PB
RWBL-PB
Eastern Meadowlark +
Red-winged Blackbird --
Dickcissel
Grasshopper Sparrow
Vesper Sparrow
Figure 1: (L) Representative soybean rowcrop field. (R) SAFE field after first season of conversion to grassland habitat from rowcrop such as Soy or Corn.
Background:
While investigating conspecific behavior in Grasshopper Sparrows (Ammodramus savannarum), we observed higher densities of Eastern meadowlarks (Sturnella magna) in sites containing added sparrow song. From these observations we set out to understand potential heterospecific interactions in grassland bird communities for the 2012 breeding season in Illinois.
Objectives:
To investigate the potential heterospecific information use in grassland birds.
Conduct playback experiments with 3 treatments (EAME, RWBL and Silent) during the 2012 breeding season.
Compare densities of bird species commonly found in grassland communities for playback experiments across breeding seasons.
Introduction
Table 1: (+/-) indicate a positive or negative association with respective playback treatment types. Zeroes indicate no trend.
Conclusions
Conspecific attraction was observed in Grasshopper Sparrows and Eastern Meadowlarks. Vesper Sparrows showed some tendency to be attracted to 2012 playbacks and avoidances occurred with Red-winged Blackbirds in response to Eastern Meadowlark playbacks.
Heterospecific attraction between pairs of species is inconsistent and not reciprocal between species pairs in grassland birds. Other studies have shown similar results where one species was favored over others as an information source (Thomson et al., 2003)
Heterospecific information and attraction has been shown to be used for migrating, habitat selection, predator signaling and increased foraging efficiency (Monkkonen et al., 1999;Thomson et al., 2003;Ward et al., 2010). In our study, we worked explicitly in the breeding season. Conspecific attraction appears to be stronger than heterospecific attraction in grassland bird habitat selection suggesting conspecific information may be more valuable during breeding.
Figure 3: Densities of common grassland birds in Illinois in response to Grasshopper Sparrow Playback treatments and silent controls for 2010 and 2011 breeding seasons. Red boxes = conspecific response; Green boxes = heterospecific response. Twelve sites were used in 2010 and 20 in 2011 (Total N=32).
Acknowledgements:
Many thanks to Patricia Graves, Wade Louis and Carle Handel for helping make landowner contacts. Also thanks to the wonderful landowners of Illinois for giving me permission to do this research on their property. Funding was provided by the College of Agricultural, Consumer, and Environmental Sciences (University of Illinois),the Illinois Department of Natural Resources and the Illinois Ornithological Society.
Figure 2: (L) Deployed playback station in newly planted SAFE sight. (R) Automated playback equipment
Methods
Field Sites:
Sites were chosen from the State Acres For Wildlife Enhancement (SAFE) program, a type of Conservation Reserve Program (CRP) that creates new grassland habitat from rowcrop agriculture fields. All sites were a minimum of 1km away from any other field and all were of various sizes and shapes from 6-40 ha. Playback:
We used two playback types (EAME & RWBL) and a silent control. Stations were randomly assigned to our field sites so that each of the three treatments were applied to six sites (N=18). Point Counts:
We conducted 10 minute point counts at each site once a week for 10 weeks (May – July) and then calculated densities from those data. Analysis:
We used Distance 6.0 to calculate densities. We then used SAS 9.3 to test for treatment effects on bird densities using procMIXED. We also sampled habitat and analyzed those data using principal component analysis (PCA).
Literature Cited:
Ahlering, M. A., D. H. Johnson, and J. Faaborg Conspecific attraction in a grassland bird, the Baird's Sparrow. Journal of Field Ornithology 77:
Monkkonen, M., R. Hardling, J. T. Forsman, and J. Tuomi Evolution of heterospecific attraction: using other species as cues in habitat selection. Evolutionary Ecology 13:
Thomson, R., J. Forsman, and M. Monkkonen Positive interactions between migrant and resident birds: testing the heterospecific attraction hypothesis RID A Oecologia 134:
Ward, M. P., and S. Schlossberg Conspecific attraction and the conservation of territorial songbirds. Conservation Biology 18:
Ward, M. P., T. J. Benson, B. Semel, and J. R. Herkert The use of Social Cues in Habitat Selection by Wetland Birds. Condor 112:
Figure 4: Densities of common grassland birds in Illinois in response to Eastern Meadowlark and Red-winged Blackbird playback treatments and silent controls for 2012 breeding season. Red boxes = conspecific response; Green boxes = heterospecific response. We used N=18 sites for these experiments.