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Abstract

Mule deer numbers have declined precipitously in the San Andres Mountains of southcentral New Mexico. To assess reasons for population declines, we monitored condition, survival, and causes of mortality for a range of 37 to 64 radio-collared, >1.5-year-old female mule deer annually, and a range of 14 to 31 radio-collared, >1.5-year-old male mule deer annually from 2003 to 2009, and modeled environmental factors affecting survival. We found annual survival rates of 0.74 to 0.86 for females and 0.74 to 0.92 for males, rates that were similar among years within sexes. Causes of mortality for 50 radio-collared females and 22 radio-collared males included predation (13 females, 2 males), accidents (4 females, 1 male), malnutrition (13 females, 7 males), disease (6 females, 2 males), unknown-not-predation (3 females, 6 males), unknown (11 females, 3 males), and harvest (0 females, 1 male). Condition of females varied among years and was poor in most years (i.e., lactating females had <7% body fat). Probability of survival of individual females was most closely related to indices of muscle and body mass in late autumn at the annual peak of condition, whereas probability of survival of individual males was unrelated to size or condition. Probability of survival of individuals of either sex was not related to any index of condition or size at the seasonal low of condition in late-winter, lactation or pregnancy status, geographic location, or any measure of annual or seasonal precipitation. Mean annual survival rates of both males and females were negatively correlated to total precipitation during July to September (primary lactation period), but female survival was positively correlated to total precipitation from January to June (conception–parturition). Ratios of fawns to adult females during April 2005 to 2010 ranged from 31 to 57 fawns/100 adult females, and maximum potential rates of increase (λ) showed a significant positive rate of increase only in 2004 and 2005 (P [λ > 1.0] > 0.937). Potential rates of increase of mule deer in the greater San Andres Mountains were limited by production and survival of fawns, rather than adult mortality.

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