Capture histories of owls with covariates for survival analysis

Early life experiences have carry-over effects that manifest in later life
stages. Challenging rearing environments result in more energy invested in
immediate survival and less energy on growth and maturation, which can
decrease survival in both the short and long term. One way to measure
differences in energy allocation to growth between individuals is through
physiological indices, such as concentrations of the metabolic hormone
corticosterone, and body condition. Corticosterone increases in response
to challenges to homeostasis and mobilizes stored fat and muscle to meet
energetic demands. Maintaining elevated corticosterone can result in poor
body condition and decreased survival. Juvenile or pre-breeding age
classes are typically a substantial portion of the total population and
serve key functions in population dynamics in many long-lived species.
Thus, understanding how the rearing environment may influence demographics
across life-history stages is crucial to understanding larger population
dynamics. Yet, demographic models and conservation planning often lack
vital rate estimates for early life stages because, prior to breeding,
animals cannot be effectively sampled (i.e., they are unobservable). We
used corticosterone concentrations in feathers and body mass of fledged
juvenile Northern Spotted Owls (Strix occidentalis caurina) as indicators
of potential energetic limitations early in life and used a multi-state
modeling framework to quantify the effect of these indicators on apparent
annual survival prior to claiming a territory (pre-territorial birds) and
the probability of recruiting into the territorial population. Apparent
annual survival for pre-territorial birds was higher for birds with
greater mass, earlier banding dates, and intermediate levels of
corticosterone. Birds with greater mass at banding were also more likely
to recruit into the territorial population. Our results demonstrate the
importance of early development and traditionally excluded life-history
stages on long-term demographics. Although early life stages are difficult
to observe, monitoring and conservation efforts may be improved by
increasing studies on pre-territorial animals, control of Barred Owls, and
conservation of forest structures important for Spotted Owls. This may
contribute to increased juvenile survival and recruitment.