Survival and Reproduction

Climate Change is Inducing Stress:

Studies by Franklin and Carrol suggest that there is a strong role in the effects of climate change on the Northern Spotted owl’s reproductive success and hatchling survival.  Owls have the highest energy output during the breeding season rather than winter (Wijnandts, 1984), so the effects of climate change will be greatest during the spring. Increases of precipitation during this season can decrease hunting efficiency, prey activity, and prey population. Maintenance of patch variation in old growth forests will also be crucial so the owls won’t exhaust particular prey patches, so maintaining  “dispersed patches of different vegetation types and seral stages with in a matrix of mature and old-growth forest may provide a stable prey resource that buffers against the effects of climate on prey population, and hence the spotted owls.” (Frankin et al. 2000)

Early Nesting Period (March to April)

Figure 1 depicts that changes from a warm and dry nesting season in the spring to a wet and cold one can have serious detrimental effects on the owl's survival. Predicted reduction of survival can be as great as 26% if the habitat quality is poor. Figure 1 also portrays the importance of maintaining a high quality habitat as "key landscape habitat components, and shows that a good habitat can buffer the negative consequences of climate change on these owls. As the loss of mature and old-growth forest can exacerbate the effects of unfavorable climatic conditions on survival. " (Franklin et al. 2000) This again shows and reiterates the unfavorable effects of the loss of primary old growth forests and also the direct effects climate change can have on these owls if precipitation abundance is manipulated in the early nesting season. Climate conditions during the early nesting period may exacerbate an energetic
stress on an individual by decreasing its time to starvation.

Fig. 1: Predicted survival decline (climate/habitat models) due to the transition from optimal warm (early nesting season) spring to cold, wet spring : 7%, 17%, 26%  in good, medium, poor habitat respectively. 17.5% as the climate gradient progressed from the ideal warm/dry spring to a cold wet spring.( Franklin et al. 2000, Figure 11)

Precipitation Effect on Late nesting season (May): 

As if the impacts of precipitation effects due to climate change wasn't enough, the effects on the late nesting season is worth investigating as well. With increased precipitation during the late nesting season, the survival of the young are impacted. Since the increased precipitation affects the parent owls to forage and feed the young, their survival takes a negative impact. Figure 2 portrays the reduced reproductive output with the increasing precipitation due to climate change. Increased precipitation after young have hatched, prevents efficient foraging by adults, reducing prey supplies, and "causing direct mortality of young through chilling." (Franklin et al. 2000)

Fig. 2 : Annual reproductive output of NSO relative to number of days of precipitation during late nesting period. Increased precipitation decreases the annual reproductive output of the spotted owl. ( Franklin et al., 2000, Fig. 4b)