Sharp-Tailed Grouse (Tympanuchus phasianellus) Habitat Selection and Population Trends in Saskatchewan

Abstract

The sharp-tailed grouse (Tympanuchus phasianellus) is a symbol of Saskatchewan and has important cultural and economic status in the province. Over the last few decades this species has been declining in Saskatchewan, especially in southern grassland regions. While the decline in sharp-tailed grouse populations has been variously attributed to habitat loss, degradation, and fragmentation, the major factors affecting population trends remain to be definitively identified. Two areas of importance for research were highlighted by provincial government scientists to inform long-term management and conservation of sharp-tailed grouse in Saskatchewan: (1) identify sharp-tailed grouse habitat and its distribution in the province; and (2) understand population changes in relation to weather conditions. My research was undertaken to address these knowledge gaps for the plains subspecies of the sharp-tailed grouse in Saskatchewan. Leks, communal dancing grounds, form the basis for much of the life history knowledge of sharp-tailed grouse and are often used in the management of the species. Correspondingly, the probability of lek occurrence is an excellent indicator of habitat quality. However, the specific characteristics of the landscape around leks that draws sharp-tailed grouse to an area are still relatively unknown. To study the habitat distribution of plains sharp-tailed grouse in Saskatchewan, I identified lek locations using both contemporary field surveys and historical data collected by the Saskatchewan Ministry of Environment (MOE). I generated a habitat suitability index (HSI) model, which provides a probability of lek occurrence using the known locations compared to various landcover types. I included two variations of each landcover type variable in the HSI: one at a 1x1 km scale and another at a 5x5 km scale. The most important predictors for lek occurrence from the model were the proportion of grasslands at 5x5 km, followed by the amount of grassland within 1x1 km. After the proportion of grasslands, the next most important predictors was the roughness of the landscape (number of topographic changes, with flatter areas being preferred), and the proportion of wetlands, both at the 5x5 km scale. These results together highlight the importance of managing large, heterogenous grassland areas for the occurrence of sharp-tailed grouse leks. Annual changes in weather can have a variety of influences on avian population sizes, either directly or indirectly. I focused solely on the factors which are likely to have direct effects on sharp-tailed grouse. Lek counts are often used as an index of local population sizes due to their centrality to the life history of sharp-tailed grouse, the high site fidelity that male grouse show to leks, and the ability to easily count birds on leks. I tested the effects of the average winter temperature, total summer precipitation, and the average spring temperature on annual lek counts from 1970 to 2004, all of which have been shown to affect sharp-tailed grouse in previous research. Colder winters led to lower average lek counts; whereby average winter temperatures of -25oC resulted in leks losing on average one male compared to the average lek count. In contrast, lek counts had a quadratic relationship with summer precipitation with lek counts reaching a peak at moderate precipitation levels and declining at both low and high levels. The largest declines in lek size were associated with precipitation levels around 30 cm, resulting in the loss of an average of 3-4 males per lek. By better understanding how these annual weather conditions can affect the populations of sharp-tailed grouse, managers can make more informed decisions earlier to better set bag limits.