Non-invasive Determinants of Neonate Condition: California Sea Lions (Zalophus californianus) as a Case Study
Green, David S.; Young, Julie K.; Hernandez, Claudia J.; and Gerber, Leah R.
School of Life Sciences, Arizona State University
Obtaining population trend data can be problematic when study sites are difficult to reach or the species being studied is sensitive to human disturbance. Population trends are important for determining the fitness and status of animal populations, and the body condition and growth of offspring can serve as proxies for measuring population status. We propose that, for California sea lions, (Zalophus californianus), non-invasive observations of neonate behaviors could act as a substitute for invasive approaches to measuring condition and growth. To examine this idea, data on pup behaviors were compared to measurements of condition and growth on three islands located in the Gulf of California, Mexico. We found that pups with low body conditions and growth rates nursed the most, pups with low condition and high growth rates exhibited more inactive behaviors, and pups with good condition and low growth rates engaged in more active behaviors. However, body condition and offspring growth may not be correlated with population status at each site. Therefore, we conclude that non-invasive means to gather information about individuals may be used to shed light on their specific status, but it is unclear if this strategy explains population dynamics.