Birth Timing for Mountain Lions Figure 1. Number of litters born during each month from 2005 to 2009 for mountain lions (Puma concolor) in the Black Hills, South Dakota, USA. doi:10.1371/journal.pone.0044625.g001 late pulse (August), autumn (September–October) and winter (November–March, Table 1). Cub body mass We used data for 74 (34M, 40F) cubs originally captured in natal dens, at ages ranging from 1–4 weeks, to estimate influence of birth timing on weight at 1 week of age. We found few cubs born during winter (n = 4), so we censored those animals from analyses regarding cub weights. We found that timing of birth (F1,61 = 3.850, 2-sided P = 0.016) and litter size (F1,61 = 3.801, 2- sided P = 0.056) influenced body mass of cubs at 1 week of age, whereas sex (F1,61 = 0.624, 2-sided P = 0.866) had no effect. Mean body mass for male (n = 34) and female (n = 40) cubs at 1 week of age was 1.162 kg60.112 (SE) and 1.102 kg60.095, respectively. There was a declining trend in body mass as litter size increased. Mean body mass of cubs in 2-, 3-, and 4-cub litters were 1.114 kg60.135, 1.053 kg60.091, and 0.912 kg60.089, respec- tively. Cubs born in litters of 2 were 22% larger at 1 week of age than cubs in litters of 4 (Extra sums-of-squares F1, 68 = 3.308, 2- sided P = 0.146). After accounting for sex and litter size, mean mass of cubs born within the birth pulse (June–August) was similar to cubs born outside the birth pulse (Extra sums-of-squares F1, 61 = 2.40, 2-sided P = 1.0); however, a trend existed, with cubs born in spring lightest and body mass of cubs increasing through autumn (Extra-sums-of- squares F1, 62 = 3.98, 2-sided P = 0.102). Cubs born during spring and early pulse averaged 230 g672 (SE) lighter in mass than cubs born during the middle pulse through autumn (Extra sums-of- squares F1, 60 = 12.302, 2-sided P = 0.002). When we reevaluated birth timing relative to ungulate birth periods, we found a strong relationship to timing of birth and weight at 1-week of age (F1,61 = 4.310, 2-sided P = 0.004). Cubs born before the ungulate birth peak (n = 10) weighed 869 g (mean)696 (SE) whereas cubs born coincident with ungulate birth Table 1. Environmental characteristics exhibited during annual periods and the number of documented mountain lion (Puma concolor) cubs born during each period in the Black Hills, South Dakota, USA. Period Spring Early Middle Late Autumn Winter Months April–May June July August September–October November–March doi:10.1371/journal.pone.0044625.t001 No. cubs Environmental Characteristics 12 13 15 16 13 4 Variable snowfall and cold temperatures; adult-sized ungulates with relative lowest availability Warm days, cool nights; neonate ungulates present, but in ‘‘hider’’ phase resulting in low availability Warm days, warm nights; neonate ungulates present and in ‘‘flee’’ phase resulting in highest availability Warm days, warm nights; adult and juvenile ungulates present resulting in high availability Cool days; cool nights; adult and larger juvenile ungulates present resulting in high availability Snow; cold days, cold nights; adult-sized ungulates available, post-hunting season results in declining availability and harsh environmental conditions. PLOS ONE | www.plosone.org 2 September 2012 | Volume 7 | Issue 9 | e44625