When we think of scavengers, we think of vultures lazily circling the skies waiting to eat the roadkill on side of the road. Being a scavenger is seen as being too lazy to work for your own food, instead, you settle for eating “leftovers”. The phrase “beggars can’t be choosers” comes to mind when we think about why scavengers settle for dead carcasses left by others.
In high school, we learn that heterotrophs cannot produce their own food source, and so obtains food or energy from other organic substances. And when we get to predators, it is often simplified into “predators” and “scavengers” as consumers of other animals, often neglecting to show the complex interactions between scavengers and carrion and how it can impact the stability and overall health of an ecosystem. So what exactly affects this network of scavenger-carrion interactions? In a study by Turner et al., it is suggested that previous studies could have either over or underrepresented scavenging communities from neglecting to include carcass size and habitat type in their research.
The study was conducted in four different habitat types which were sorted based on the age of the surrounding trees (clearcut, 1–2 yr; mature hardwood, 23–95 yr; immature pine, 11–26 yr; and mature pine forest, 28–75 yr) and three carcass sizes (rat, rabbit, and wild pig). These carcasses represent small, medium, and large respectively. Trials were conducted in two seasons to reflect the effects of seasonal differences in invertebrate and bacteria activity.
So what did they find? Scavengers were found to consume 100.0% of rabbit carcasses placed in clearcuts, while vertebrates scavenged rabbit carcasses placed in hardwoods, immature pine, and mature pine less frequently. For rats and pig carcasses, vertebrate consumption was balanced throughout the different habitats. In hardwoods and immature pine, pig carcasses were consumed at a higher frequency. When factoring in the weather, it seems that during warm and cool seasons, pig carcasses stayed the same frequency of being consumed, while rats and rabbits showed a noticeable decline in being consumed during cooler temperatures. They have also found that during cooler seasons, vertebrates scavenged rats less frequently than pigs and rabbits. Detection time of scavengers finding their food source also seems to increase depending on the temperature, suggesting that cooler temperatures hinder the vertebrate’s ability to find food (Fig.1)
These results suggest that vertebrates are efficient at locating the different carcasses in warmer months when invertebrate and microbial communities are most active. However, in the cooler months when invertebrate and microbial communities have lower activity, the detection rates decreased due to reduced olfactory cues from the lower temperatures. Carcass size is also important, as the results show that the larger the carcass, the more likely it is for the vertebrate to detect carrion. Foliage and dense vegetation could reduce the success of vertebrates that rely on vision to scavenge, while olfaction had a better chance at detecting carcasses amongst the vegetation. The composition of vertebrates at each size of carcasses has some overlap, but there was a trend of medium-sized predators eating small and medium carcasses more often, while dominant mammals and scavengers were found more often at the pig carcasses.
Overall, carcass size, habitat type, and season all play important roles in vertebrate scavenger ecosystems. This study builds on previous research on carrion recycling and the role of scavengers and vertebrates in this complex cycle. The results indicate that studies from here on out should incorporate the carcass sizes and habitat types, which can give better insight into the scavenger community. This opens up more fields of research under vertebrate scavenging ecology, such as understanding the impacts of anthropogenic activities to ecosystems and how they could potentially affect scavenging communities.
Turner, K. L., Abernethy, E. F., Conner, L. M., Rhodes, O. E. and Beasley, J. C. (2017), Abiotic and biotic factors modulate carrion fate and vertebrate scavenging communities. Ecology, 98: 2413–2424.