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.

We used capture histories, feathers, and banding data collected from 2001 to 2017 as part of a long-term demographic monitoring program for Spotted Owls (e.g., Lint et al. 1999). Study areas included Cle Elum and Olympic Peninsula in Washington state, and Coast Range, H.J. Andrews, Tyee, Klamath, and South Cascades in Oregon state (Figure 1). These study areas cover almost 10% of the range of Spotted Owls and have varying topography, climate, land management, and forest structure, as described in prior publications (e.g., Forsman et al. 2011, Dugger et al. 2016). Cle Elum, Coast Range, Tyee, and Klamath study areas contain a blend of federal and private lands, while Olympic Peninsula, H.J. Andrews, and South Cascades largely cover federal lands.

Our field crews monitored historic Spotted Owl territories annually, using standard protocols to estimate occupancy, survival, and reproductive output of individually marked owls (Franklin et al. 1996). After juvenile owls left the nest, surveyors captured and banded owls with individually numbered U.S. Fish and Wildlife Service bands and color bands. When crews recaptured birds marked as juveniles for the first time, they confirmed their USFWS bands and replaced their cohort-specific color bands with a unique color-band that allowed identification of birds through resighting alone (Forsman et al., 1984).

During banding, field crews weighed birds and collected small samples of body feathers from the breast, back, or head, placed them in plastic bags, and stored them at room temperature (19–22° C). We collected feathers opportunistically, thus the number and feather tract sampled varied. All relevant state and federal permits were acquired and maintained for all study areas, and protocols for handling owls were approved under animal care and use permits overseen by Oregon State University’s Institutional Animal Care and Use Committee.