Author: Lina Potas

Building urban predator-prey networks using camera traps

Posted on by Lina Potas

Urban trophic systems that involve mammals are a largely understudied field. Barriers to this research include the cost of conducting field observations or DNA analyses. Camera traps can be a cost-effective method to opportunistically record predator-prey interactions. Potential prey encounters can also be recorded with camera traps and used to build trophic networks. 

This study was conducted in Toronto, Canada, a highly urbanized area. The focal predator species were red foxes and coyotes because they have opportunistic diets and have adapted to thrive in urban areas. 33 motion-detecting cameras were placed at approximately knee height on trees and lamp posts along previously laid transects throughout the city from October 2020 to September 2021. Any image containing more than two animals was considered a predation event. Potential predation events were recorded as each species was detected on the same camera less than five minutes apart. This data was used to create bipartite networks that demonstrate the urban predator-prey interactions and potential interactions. Their results found a total of 43 combined predation events and 299 combined potential interactions for red foxes and coyotes. 

Images of recorded predation events by coyotes (uppers) and red foxes (lower)

The first thing this paper failed to address was the impact of COVID-19 protocols in urban areas on these predator-prey interactions. I suspect that over the course of the study, restrictions lessened, which would likely be associated with a decline in these interactions in urban areas, as we have discussed in class. Regarding the researchers’ methods, site-specific information should’ve been included in their analysis of interactions to develop a more intricate food web of the whole study area. I also think it would be important to note whether the prey or predator was detected first when documenting potential predator-prey interactions. The difference could be significant enough to remove some of the observations as potential interactions. Also, the researchers of this paper urge future researchers to consider the likelihood of a predation event in their analysis of potential encounter events, which could also result in a more detailed food web. 

When Owls Go To Town: The Diet of Urban Barred Owls

Posted on by Lina Potas

Urban areas commonly develop in formerly biodiverse habitats, such as wetlands and valleys. This development tends to lead to an overall decrease in biodiversity, but some raptors have adapted their predation strategies to thrive in urban ecosystems. However, urban environments can also pose a higher threat to raptors through anthropogenic causes, such as window strikes and exposure to chemicals. This is especially true of anticoagulant rodenticides (ARs), which are primarily used on rodents in urban settings. The aim of this study was to determine the if exposure to ARs in barred owls stemmed from consumption of rodents with ARs in their system, or if secondary exposure from predating at bait stations caused the exposure. 

Owl pellets and prey remains were collected at nesting and roosting sites in and around Vancouver, British Columbia, Canada. The sites were found by local chapters of naturalist clubs, and playbacks were used at said sites to determine presence of barred owls. Bait stations of ARs were also scouted and their locations and distances from nests were marked. After collection, the pellets were dissected, and prey items were identified. 

The researchers found that the primary prey product of their studied owls was young adult rats. Barred owls with higher urban development surrounding their nests and roosts also had an relatively larger proportion of rats in their diets. Because rats are one of the primary targets of ARs, barred owls are subsequently at risk for posioning from secondary exposure to ARs. 

This study does state that barred owl in urban areas in British Columbia are at risk for secondary AR exposure, it never discusses if there is a risk for primary exposure. Primary exposure is mentioned in the abstract and background information, but not in the results, so readers do not know if this is also a reason for concentrations of ARs in barred owls. Furthermore, the researchers do not discuss how these results could apply to other urban areas. Doing so might be considered speculation, but I would like to know more about how we can use their results more broadly. I also would’ve liked to know more about black bait stations used to deploy ARs, so I could know specifically how they are affecting barred owl predation efforts. 

Hindmarch, S. and Elliot, J.E. When Owls Go To Town: The Diet of Urban Barred Owls. Journal of Raptor Research 49 (1): 66-74. https://doi.org/10.3356/jrr-14-00012.1