In this post Ryan Fisher discusses his paper ‘Extreme precipitation reduces reproductive output of an endangered raptor‘ in the latest Issue of Journal of Applied Ecology
When we think of threats to species around the globe, we typically think of the usual, and very important, culprits of habitat loss and fragmentation. Unfortunately, the large and sometimes catastrophic effects of extreme weather on wildlife often get overlooked. Grassland birds are especially vulnerable to extreme weather because they and their nests may be directly exposed to wind, temperature extremes, and rain during the breeding season. Hunting for prey to feed young chicks also gets much more difficult during bad weather. Unfortunately, many climate change scenarios predict that breeding birds and other wildlife will be exposed to both an increasing frequency and intensity of extreme weather in the future.
The burrowing owl is a small grassland-associated raptor that lays eggs and raises its young in an underground burrow. In Canada, the burrowing owl is considered an endangered species and their population has declined by about 90% since the 1990s. Researchers think that the combined effects of habitat loss and climate change may have contributed to these recent declines.
We used a two-pronged approach to evaluate the impacts of extreme weather on burrowing owl populations in western Canada: observational and experimental studies. Through a massive collaborative effort to regularly monitor breeding burrowing owls and their nests throughout Alberta and Saskatchewan, Canada, we documented how many young each nest produced and identified causes of failed nests. We also conducted a small experiment over 3 years where we provided extra food (dead mice or quail) for some burrowing owl nesting pairs and no extra food for others. By combining our observations and experimental outcomes with weather data, we have gathered new insights into how burrowing owls are affected by extreme weather.
In fact, extreme rain events in prairie Canada are pretty tough on burrowing owls. When the total amount of rainfall in one day exceeded 20 mm, burrowing owl nests flooded, generally leading to the death of all the chicks in a nest. But perhaps a more sinister, and tougher to detect, impact of extreme rainfall, was the consequence for nests that didn’t flood; our feeding experiments helped us detect this impact. In nests that were not provided with extra food throughout the breeding season, the youngest chicks in each nest died during bad weather, while many of their older siblings survived. But, when we provided extra food for the owls, the youngest chicks seemed to be able to “weather the storm” and survive at rates that were comparable to their older siblings. In the wettest summers, burrowing owls, on average, had 1 fewer chicks survive to leave the nest compared to owls nesting during drier summers.
What does this all mean for the long-term management of burrowing owls?
To date, management activities in Canada have focused on creating and restoring nesting habitat. In light of our results, we suggest that managers also need to focus on providing suitable habitat for prey, and also habitat where burrowing owls can easily access that prey. Then, adult burrowing owls will be better able to catch and store enough prey to ensure young chicks will receive enough food during bad weather.
And although providing food to burrowing owls and their chicks seems like an attractive option, we think that it could not be done over an area broad enough or a time period long enough to halt or even reverse population declines in Canada. In emergency situations, feeding burrowing owls could be considered as a management option similar to supplemental feeding programs for other raptors and vultures.
To address the issue of nest flooding, we need to encourage conservation and restoration of upland pastures that are less prone to flooding. Conservation and restoration of upland habitat will also benefit several other prairie ground-nesting birds that experience similar nest flooding issues.
Unfortunately, for burrowing owls and other endangered species, it appears that conservation and recovery is going to become even more difficult with the added threat of more frequent and intense extreme weather.