Abstract
Assessing the health of wildlife populations is critical to achieving conservation goals; however, proper assessments can be complicated when study sites are difficult to reach or when focal species are sensitive to human disturbance. Condition and growth of offspring may indicate population health, but obtaining such data generally relies on invasive techniques. Here, we examine the extent to which noninvasive observations of neonate behaviors could serve as a proxy for traditional approaches to estimating neonate body condition and growth of a wild pinniped, the California sea lion (Zalophus californianus), in the Gulf of California, Mexico. Generalized linear models and multiple linear regressions were used to examine the effect of sex, breeding island, year, and neonate behaviors (e.g., nursing, active) on body condition and growth rates. We found a strong correlation between individual growth rates and behaviors of male neonates. Males engaged in proportionally more active behaviors had lower growth rates (β = –0.0005), whereas males engaged in proportionally more nursing events had higher growth rates (β = 0.002). There was no relationship between neonate behavior and condition for either sex, nor between behavior and growth rates of female pups. These results provide insight into the possibility of using behavior as an indicator of individual status of males that could facilitate assessments of population status and illustrate the importance of using alternative approaches to measure animal condition for species conservation.
Highlights
Neonate condition may be a useful indicator of population health in mammals, yet most studies focus on general demographic indicators such as population size and vital rates (White and Lubow 2002, McMahon et al 2005)
La variable sexo fue el factor que más afectó las tasas de crecimiento de los lobos marinos de California en el Identifying non-invasive relationships between animal condition and behavior is important in light of the effects of human disturbance on animal behaviors (e.g., Allen et al 1984, Boydston et al 2003, Rode et al 2006)
The development of non-invasive approaches to assess population health may assist resource managers interested in determining current population demography and health without influencing current and future population trends that may be affected by human disturbance
Summary
Neonate condition may be a useful indicator of population health in mammals, yet most studies focus on general demographic indicators such as population size and vital rates (White and Lubow 2002, McMahon et al 2005). More in-depth details of neonate condition (e.g., growth rates) may enhance our understanding and predictive capacities of population trends because the condition of individuals is directly related to the population to which they belong (Unsworth et al 1999, Pojar and Bowden 2004). Body size and condition influence the survival of all age classes (Clutton-Brock et al 1997, Boltnev et al 1998), often with the largest impact on neonates and juveniles because of their inexperience in searching for prey and their undeveloped immune systems (Singer et al 1997). For many long-lived vertebrates, variation in newborn and juvenile survival probabilities may have a higher impact on population growth rate than on other vital rates (Eberhardt 1985, Crone 2001, Underwood et al 2008)
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