and bighorn sheep as well as domestic livestock species. No other large carnivores were present in this system. Bobcat (Lynx rufus) and coyote (Canis latrans) are mesocarnivores that occur sympatrically with mountain lions. Field Methods.—We used foot-snares [22], trained hounds [23], and cage traps [24] to capture adult female (.3 yrs) mountain lions throughout the year. We used a mixture of telazol and xylazine and administered them at recommended dosages [25]. We aged mountain lions by tooth wear and pelage characteristics and noted previous reproductive activity [26]. We outfitted each mountain lion with a radiocollar (MOD-500, Telonics, Mesa, Arizona, USA) and relocated radiocollared mountain lions 1-time per week by using homing-telemetry techniques from a fixed-wing aircraft [27]. We used homing techniques while on foot for females where $2 aerial telemetry locations were within 500 m of each other over a 3-week period. Closer investigations normally revealed adult female mountain lions located within nursery dens [1,28] with newly-born cubs. We captured all cubs by hand without chemical immobilization, often while the mother was away from the site [1]. We determined sex and age of cubs by tooth eruption and appearance of eyes (e.g., open or closed; [29]). Based on tooth eruption patterns and relatively young age of cubs, birth dates were within a few days to ,2 weeks of the true birth date. At the time of capture, we gave each cub a unique tattoo and some were radiocollared with small, expandable collars (MOD- 125, Telonics). When cubs were approximately 9 months old, we recaptured them by using the same techniques as those used for adult mountain lions and refitted cubs with larger radiocollars (MOD- 500, Telonics) or global positioning system (GPS) collars (single D- cell, Northstar, Virginia, USA). We used fixed-wing aircraft or satellite-telemetry to relocate subadults and mothers. When a juvenile mountain lion left the natal area, we recorded the mid- date between the last location in the natal area and the first location outside the natal area. In some cases, dispersing mountain lions made exploratory movements and returned to the natal area and subsequently left again or established a home area at least partly overlapping the natal area (e.g., female philopatry). We recorded dispersal age as the mid-date the juvenile made the initial exploratory movement, regardless of subsequent return to the natal area. If an animal was not located outside the natal area until the animal became 3 years old, we censored the animal from analyses. These animals were censored because exploratory movements can be of short duration [30,31] and frequency of weekly telemetry flights might not have detected exploratory movements. We plotted all birth dates and defined the birth pulse as the period where $40% of births occurred and number of births were higher than expected [1,4]. We delineated the births as within or outside birth pulse months and also as early (1st one-third), middle (central one-third), late (final one-third), and outside pulse. In References 1. Logan KA, Sweanor LL (2001) Desert puma: evolutionary ecology and conservation of an enduring carnivore. Washington: Island Press. pp. 1–463. 2. Rutberg AT (1987) Adaptive hypotheses of birth synchrony in ruminants: an interspecific test. American Naturalist 130: 692–710. 3. Robinette WL, Gashwiler JS, Morris OW (1961) Notes on cougar productivity and life history. Journal of Mammalogy 42: 204–217. 4. Laundre´ JW, Herna´ndez L [2007) Do female pumas (Puma concolor) exhibit a birth pulse? Journal of Mammalogy 88: 1300–1304. 5. Hemker TP, Lindzey FG, Ackerman BB (1984) Population characteristics and movement patterns of cougars in southern Utah. Journal of Wildlife Management 48: 1275–1284. 6. Beier P (1995) Dispersal of cougars in fragmented habitat. Journal of Wildlife Management 59: 228–237. Birth Timing for Mountain Lions addition, we delineated cub births as before ungulate birth peak (before 1 June), before neonate ungulates switch predator avoidance strategies (hiding vs. fleeing [11,14]; 1 June–23 June), ,60 days after strategy switch (23 June–23 August), .60 days after strategy switch (23 August–23 October), and winter (December–February). In our study area, deer and elk dominate the diets of mountain lions (Smith and Jenks, South Dakota State University, unpublished data). The birth peak for mule deer was 7–14 June [32], for white-tailed deer it was 7–17 June [33], and for elk it was 28 May–4 June (Schmitz 2010, South Dakota Game, Fish, and Parks, unpublished data). Analysis We used JMP 8.0 (SAS Institute, Cary, North Carolina, USA) statistical software to perform statistical analyses. We used chi- squared test for independence to determine if the monthly distribution of litters was uniform through the year [1,4]. We used MANOVA to examine the influence of birth timing on body mass and age of dispersal of mountain lions, while accounting for other potential influences (i.e., sex, litter size, age at capture). We used extra sums-of-squares F-tests within a MANOVA framework to test for differences in birth timing, while accounting for differences in sex, litter size, and age at capture. We used a known- fates model in Program MARK [34–36] to estimate survival. We used a 2-sample t-test to determine if differences in survival occurred between male and female cubs, despite timing of birth. We ran Program MARK analyses with and without sex as a covariate to determine if sex was related to survival. We analyzed cub survival in 2 ways. First, we placed cubs in categories; within or outside of the birth pulse to replicate the analysis conducted by Laundre´ and Herna´ndez [4]. Second, we delineated the birth pulse according to our description of the predator-avoidance strategy switch, which provided a more detailed examination. To investigate the role of mother’s age on birth timing, we calculated the monthly frequency distribution of litters born by mother’s age (i.e., 3–4 yrs, 4–6 yrs, .6 yrs). We also calculated the monthly frequency distribution of litters born by litter sequence (i.e., 1st litter, .1st litter). We visually compared birth month frequencies by mother’s age and litter sequence. Acknowledgments We thank South Dakota Game, Fish and Parks for logistical support. H. G. Shaw provided valuable comments on earlier drafts. R. W. Klaver provided provided analytical support. Author Contributions Conceived and designed the experiments: BDJ JAJ. Performed the experiments: BDJ. Analyzed the data: BDJ. Contributed reagents/ materials/analysis tools: BDJ. Wrote the paper: BDJ JAJ. 7. Sweanor LL, Logan KA, Hornocker MG (2000) Cougar dispersal patterns, metapopulation dynamics, and conservation. Conservation Biology 14: 798– 808. 8. Thompson DJ (2009) Population demographics of cougars in the Black Hills: survival, dispersal, morphometry, genetic structure, and associated interactions with density-dependence. Dissertation. Brookings: South Dakota State Univer- sity. 9. Ross PI, Jalkotzy MG (1992) Characteristics of a hunted population of cougars in southwestern Alberta. Journal of Wildlife Management 56: 417–426. 10. Robbins CT (2001) Wildlife feeding and nutrition. San Diego: Academic Press. 11. Lent PC (1974) Mother-infant relationships in ungulates. In: Geist V, Walther F, editors. The behaviour of ungulates and its relation to management. Morges: IUCN Publication 24. pp. 14–55. PLOS ONE | www.plosone.org 6 September 2012 | Volume 7 | Issue 9 | e44625