Nest predation is an important factor influencing greater sage-grouse (Centrocercus urophasianus) nests. The presence of grass at nest sites is important for sage-grouse nests because it provides cover from predators. The measurements of vegetation at nest sites typically occurs after the nests have failed or fledged, but this measurement is not reflective of the height of the grass during nest initiation. It is important to understand the rate of grass growth throughout the breeding season so that reliable models can be developed to assess habitat selection and the effects of livestock grazing on nest success. The objective of the project was to quantify the growth functions of squirreltail (Elymus elymoides) and bluebunch wheatgrass (Pseudoroegneria spicata) within sagebrush steppe. These are two common grasses that occur around sage-grouse nest sites, and little is known about their growth rates. We hypothesized that the grasses would have non-linear growth rates and that the shape of the growth functions would differ between the two species. In south-central Idaho, we set up cameras facing tufts of bluebunch wheatgrass and squirreltail with rulers placed behind them. The cameras took pictures at three-hour intervals during daylight hours between May 21st and July 18th, 2019. Fourteen cameras were focused on bluebunch wheatgrass plants and 11 were focused on squirreltail plants.
Results/Conclusions
We collected 58 days of data. Grass growth rates differed between the two species. Squirreltail grew an average of 3.5cm over the course of the study whereas bluebunch wheatgrass averaged 2.5cm of growth. Growth rates were not linear, with short periods of rapid growth followed by periods of slower growth. Growth rates of both grasses remained stable starting in late June. We have not found any other research on this topic to compare our results with, but models developed with these data may help to better understand patterns of habitat selection for this sensitive bird species.