# Thermal Characteristics of Mountain Lion Dens > How does a mountain lion mother keep her newborn kittens cool through a hot Great Basin summer? In eastern California, researchers found three dens hidden in willow and wild rose thickets so dense they had to crawl in. On the hottest days the den floor was on average 14 to 22°C cooler than the air outside. Summary by Kersey Lawrence, Original Wisdom. Updated 9 November 2026. Page: https://www.originalwisdom.com/tracking-literature/1996-bleich-pierce-thermal-characteristics-mountain-lion/ ## Citation and access - **Authors:** Vernon C. Bleich, Becky M. Pierce, Jeffrey L. Davis and Vicki L. Davis - **Year published:** 1996 - **Journal or source:** Great Basin Naturalist - **Full citation:** Bleich, V. C., Pierce, B. M., Davis, J. L. and Davis, V. L. 1996. Thermal characteristics of mountain lion dens. Great Basin Naturalist 56(3): 276–278. - **Access status:** Hosted (freely available elsewhere) - **PDF:** https://www.originalwisdom.com/wp-content/uploads/2026/11/1996_Bleich_and_Pierce_etal_thermal-characteristics-of-mountain-lion-dens.pdf ## Tags - **Species:** Mammals > Mountain lion - **Region:** North America > United States - **Behaviour and ecology:** Behaviour; Cub-rearing; Den site selection; Denning - **Methods and technology:** Analysis of covariance (ANCOVA); Analysis of variance (ANOVA); Linear regression; Radio telemetry - **Data type:** New field data - **Observer qualification:** Not needed - **Discipline:** Behaviour and ecology - **Year published:** 1996 ## Detailed keywords - **Species:** Studied: mountain lion (Felis concolor), three recently parturient females and their kittens (den 1: one male and one female kitten; den 2: three males and one female; den 3: two males and one female). Den vegetation: willows (Salix spp.) and wild rose (Rosa spp.). Area vegetation: sagebrush (Artemisia tridentata) scrub and pinyon pine (Pinus monophylla) forest. - **Location and habitat:** Mono County, California, United States, about 35 km northwest of Bishop, Inyo County (118°25’W, 37°20’N), on the western edge of the Great Basin just east of the crest of the Sierra Nevada. All three dens were along the same stream (the Owens River) at the bottom of a steep canyon, in dense riparian groves of willows up to about 4 m tall with abundant wild rose, each within 50 m of the river. Comparison (ambient) thermographs were placed less than 100 m away on north-facing slopes with sagebrush and pinyon pine. - **Topics:** natal dens; den site characteristics; thermal environment of dens; protection of young kittens from heat; canopy closure and horizontal cover; daily (diel) temperature variation; den concealment and predation risk on kittens; kitten age estimation. - **Statistics or models:** analysis of variance (ANOVA) and analysis of covariance (ANCOVA, with date as a covariate for daily solar radiation) for effects of day and time of day; simple linear regression of temperature on day of the study; t tests comparing den and ambient temperatures. Means given with standard deviations. Note on the paper: the Results describe a significant effect of “day” at den 2, while the Discussion calls it an effect of “day length”. The figure caption gives F = 1,241.07 for high versus moderate ambient temperatures, with a missing opening bracket. One diel ambient temperature test at den 3 (F = 618.443) is given without a P value. - **Data type:** New field data. Dens found in August and September 1994 and 1995. Hourly temperatures recorded at den 2 from 4 September to 4 October 1994 and at den 3 from 11 August to 16 September 1995; no thermographs were available while den 1 was in use. ## Synopsis ### 1. What they did Female mountain lions choose protected places to give birth, but little was known about these den sites. The researchers, studying mountain lion ecology in eastern California, noticed from radio telemetry that several adult females had restricted their daily movements and kept returning to the same places, a sign that they had natal dens. - Finding the dens. They searched these three areas, listened for the calls of very young kittens, and then used a trained hound to locate the dens and kittens. They estimated the kittens’ ages from published criteria. - Describing the dens. They estimated tree height, canopy closure and horizontal cover by eye at each den. - Measuring temperature. At two dens they placed a recording thermograph on the den floor and an identical one on the ground less than 100 m away, on a shaded north-facing slope, recording temperatures every hour for about a month at each den. - Comparing. They compared den and outside (ambient) temperatures by day and by hour of the day. ### 2. What they found The dens - All three dens were along the Owens River, in dense groves of willows up to about 4 m tall with plenty of wild rose, each within 50 m of the river. - Kittens at dens 1 and 3 were estimated at 20 days old or less, and at den 2 at 10 days old or less. - Canopy closure was nearly 100%, and direct sunlight never reached the ground on any midday visit. - Cover was so dense that standing researchers could not see each other at 3 m or less. The researchers could reach the kittens only by crawling in. - The den floors were littered with fallen leaves, tree trunks, branches, twigs and bark. Temperatures - Dens were cooler than the outside air in all but 2 of the paired hourly readings (less than 0.2%). - Mean ambient and den temperatures: den 2 (September to October 1994), 13.18°C outside and 6.01°C in the den; den 3 (August to September 1995), 20.47°C outside and 15.22°C in the den. - The cooling effect was strongest in hot weather. Above 31°C, the outside air was on average 21.92°C warmer than den 2 and 13.56°C warmer than den 3. That is over 3 times (den 2) and nearly 5 times (den 3) the difference at moderate temperatures (31°C and below). - Temperatures inside the dens varied less. At den 2 the mean daily range outside (28.96°C) was nearly double that in the den (15.79°C); at den 3 the outside range (32.54°C) was more than 1.5 times the den range (20.89°C). - Temperatures varied with the hour of the day at both dens. At den 2 they also changed from day to day and fell as the season went on; at den 3 there was no day-to-day effect, and the seasonal declines were smaller. - At the lowest outside temperatures recorded, the dens were not warmer than the outside air. ### 3. What they concluded - These mountain lion dens moderated high outside temperatures, supporting Shaw’s (1989) idea that dens protect young, helpless kittens from heat. - The dens gave no warmth advantage at the lowest temperatures recorded, although they might protect kittens in colder conditions than the study encountered. - Dens in thick, woody vegetation may hide kittens from predators and also shield them from direct sun. Because the den keeps temperatures more stable, kittens may need to move less to keep cool or warm, which could make them less likely to be found by predators. - The authors suggest that thermal conditions differ between types of dens (caves, rocky areas, dense thickets), and that mountain lions may choose den sites partly for the thermal advantage they give. ### 4. How tracking was or was not used No tracking by people is reported. The dens were found by radio telemetry of the mothers, by listening for kitten calls, and by a trained hound that located the dens and kittens. The paper does not describe how the hound worked. ### 6. Other technologies, skills or innovations - Radio telemetry of adult females, used to spot restricted movements around natal dens. - Recording thermographs (model RTM, Ryan Instruments) placed in pairs, one on the den floor and one outside nearby, logging every hour. - A trained hound to find dens and kittens. ### 7. Implications for conservation (from the paper) - Dense riparian willow and rose thickets provided important thermal benefits and concealment for young kittens in this area. - Den sites that reduce kitten movement may lower the chance of discovery by predators and so improve the survival of young mountain lions. ## Cite this summary Lawrence, K. 2026. Summary of: Thermal Characteristics of Mountain Lion Dens (Bleich and Pierce et al., 1996). Original Wisdom, Tracking Literature. https://www.originalwisdom.com/tracking-literature/1996-bleich-pierce-thermal-characteristics-mountain-lion/