Prey Abundance

Background:

Northern spotted owls are food specialists that mainly prey on the northern flying

squirrels, other sources include dusky-footed wood rats, and deer mice(Gutierrez et al. 1995). Since they mainly prey on the Northern flying squirrel in the Pacific Northwest it is worth investigating if warming climate is impacting the squirrels.

 Climate Change and Prey Abundance:

                 A study by Rosenberg et al. is worth noting, as he investigates the relationships between prey abundance and the Spotted Owl reproduction. A positive relationship between Spotted Owl reproduction and abundance of deer mice  (not the main prey of owl) which only consists of 1.6 % of total biomass consumed was found. (Rosenberg et. al. 2003) While the northern flying squirrel consisted of much more biomass consumption (46%), there was not a positive relationship between northern flying squirrel abundance and reproductive success.  This suggested that the owl's reproductive success was an outcome of many factors such as weather, prey, and the long lived life history. However, there is a lack of studies that identifies responses of prey populations to climate change in the PNW, therefore, we can only assume climate has affected the prey. However, his study did not conclude that the abundance of the Northern Flying squirrel had an effect on reproductive success.

            Slight changes in temperature for these high elevation Northern flying squirrels can have a big impact on their survival. As these squirrels are already living in high elevations, there is a need to move to even higher elevation. But it is “unclear to what extent G. sabrinus could shift its range to higher latitudes.” (Smith 2007) There is also implication from other scientists that the drought and stress in these forests are reducing the amount of food in the forests hence, reducing the number of flying squirrels. Other sub-species of the Northern flying squirrel are becoming endangered and possibly extinct, and this has been occurring recently. The flying squirrels feed heavily on truffles and lichens as a food supply. So with increased temperatures and droughts in many forests, its truffle fungus food, which depends on wet, cool conditions is threatened and potentially decreasing.

What this means for Northern Spotted Owls:

            The primary prey are moving to higher latitudes and avoiding competition from Southern flying squirrels that are expanding their range. This means that in order for Northern Spotted Owls to stay close to their prey they must be able to shift their ranges, but are unable to since they are habitat specialists. With the lack of old-growth forests remaining, their move would be difficult. But, since the Northern flying squirrels are habitat generalists, migration to zones outside of old-growth forests can theoretically be possible as they can exist in second growth forests. Since the owl's reproductive success was not correlated with flying squirrel abundance (Rosenberg et al. 2003) the explanation for how the owls will adapt to different prey sources remain unknown.

            This suggests that food supply can be drastically cut in the future due to range expansions and changes to the forest food supply resulting from climate change. Since Rosenberg's study did not support that the main prey abundance: the Northern Flying squirrel to be the main factor for the reproductive success of the owl, we cannot conclude that the prey abundance is the main factor for the owls decline. He suggests that multiple factors can lead to the increase and decrease of these owls, the need to investigate more factors in conjunction with prey abundance change through climate change is concluded.