DOI: 10.5061/dryad.crjdfn36g
title: Maternal survival costs in an asocial mammal: Data and analysis

description: Abstract. Maternal characteristics, social dynamics, and environmental
 factors can all influence reproduction and survival as well as shape
 trade-offs that might arise between these components of fitness.
 Short-lived mammals like the golden-mantled ground squirrel (GMGS;
 Callospermophilus lateralis) tend to maximize effort towards current
 reproduction at the expense of survival but may be complicated by other
 aspects of the species’ life history and environment.. Here, we use 25
 years of data (1995-2020) collected from a population of GMGS at the Rocky
 Mountain Biological Research Laboratory in Gothic, Colorado, to test the
 effect of several maternal characteristics (e.g., age, experience, timing
 of litter emergence), social context (e.g., litter sex ratio, kin
 density), and environmental context (e.g., date of bare ground, length of
 vegetative growing season) on survival of reproductive female GMGS using
 Cox proportional hazard models. Our results indicated that social dynamics
 (i.e., density) and environmental conditions (i.e., standardized first day
 of permanent snow cover and length of growing season) explained
 significant variation in annual maternal survival, while maternal
 characteristics did not. A higher density of related breeding females and
 the total number of females (both related and unrelated to the focal
 mother) were associated with an increase in the mortality hazard. A later
 standardized date of the first day of permanent snow cover and a shorter
 growing season both reduced the maternal mortality hazard. Together, our
 results suggest that factors extrinsic to the squirrels affect maternal
 survival, and thus may also influence local population growth and dynamics
 in GMGS and other short-lived, territorial mammal species.
description: <em><strong>Study Site & Data
 Collection</strong></em> The Rocky Mountain
 Biological Research Laboratory (RMBL) is located in the East River Valley
 of Gunnison, Colorado (38°58'N, 106°59'W). The 13-ha study site
 is situated at an elevation of 2,900 m above sea level. A complete census
 of the GMGS population at RMBL began in 1990, with detailed pedigrees
 constructed for all adult females beginning in 1995.  We used data
 collected from 1995 to 2020 on 141 resident females for which we had 249
 annual observations and 131 mortality events. Females entered the study
 the year of their first reproduction, which occurred at age one or two for
 nearly all individuals. Because we only included reproductive females, any
 instance where an individual disappeared from the study site was
 classified as a mortality event as post-breeding dispersal is extremely
 rare (&lt;1% of females, Van Vuren, unpublished).
 To develop a census database for analysis, field methods involved
 monthly trapping events during the active season and daily observations.
 Once trapped, individuals were identified by ear tag (Monel 1005-1) and by
 unique dye mark (Nyanzol-D) applied to the fur, weighed (g) with a Pesola
 scale, and assessed for reproductive status based on nipple development.
 Individuals were classified as ‘alive’ if they were trapped or seen during
 daily observations, but adult females who failed to return to the system
 were classified as ‘dead.’ For immigrant individuals that were not born in
 the study site but entered and established a territory later, we used
 timing of entrance and mass at capture as indicators of age. Immigrants
 who were captured late in summer and had a mass consistent with other
 young of the year were classified as juveniles and assigned a known age;
 by contrast, immigrants who were captured in spring could be yearlings or
 older and mass could not be used as a categorical difference, making their
 age unknown. 
description: Additional details regarding the methods and analyses are
 provided in the manuscript.