Have you ever wondered about the difference between Northwestern Crows and Common Ravens, two of Mayne Island’s Corvid bird species?
The Mayne Island Conservancy is eagerly anticipating a visit by Dr. Ben Freeman, postdoctoral fellow at the University of British Columbia to teach us more about them. At this time, we are unable to give a firm date for Ben’s presentation on Mayne, but here is some information about him and his work, plus some interesting facts about these birds to whet your appetite.
“I have studied interactions between crows and ravens across North America – basically who gets mad at whom in nature. We used citizen science observations from eBird for this study, compiling cases where people had observed crows and ravens being angry with each other.”Ben Freeman
“I want to understand the big patterns of life on Earth and ensure that today’s incredible biodiversity will persist into the foreseeable future. My research focuses on the best places on Earth—mountains— and I have an inordinate fondness for our feathered friends. I am a Banting and Biodiversity Research Centre postdoctoral fellow in Dolph Schluter’s lab at the University of British Columbia. I received my Ph.D from Cornell University in 2016 (Ecology & Evolutionary Biology). When on the job, you can find me on intense fieldwork trips, running field experiments, in museum collections, analyzing citizen science datasets, and comprehensively searching the literature. Or perhaps more likely, hard at work writing, re-writing, and re-writing once more.”Ben Freeman
Sometimes it can be hard to tell the Common Raven from the Northwestern Crow, but physically the birds differ in several ways. Ravens are larger with a wedge-shaped tail, whereas crows have a squared-off tail. Ravens have a longer bill with feathers running along it and shaggy throat feathers which they fluff up when cawing. Crows have shorter bills without the feathers and no shaggy throat. Socially, crows gather in groups known as “murders”, and ravens are known collectively as an “unkindness” or “conspiracy”!
Ravens tend to travel independently or in pairs, and may group around a carcass to feed upon it. Both birds are highly intelligent and respond to human sounds. For example, ravens ignore loud noises from cars and machinery, but will often investigate the source of gunshots in hope of finding a free meal. Both crows and ravens are incredibly intelligent members of the Corvid family, and there are many stories about their abilities to understand cause and effect, utilise tools, and recognise human faces (researchers have learned to wear face masks!).
Crows tend to gather into larger groups and inhabit cities, agricultural, and natural habitats, whereas ravens are more independent and live in wilder areas less populated by humans. Crows are particularly aggressive during spring when they are protecting their young chicks from hungry ravens, and during winter when they are fending off competitors for limited food resources. On Mayne Island, crows are often seen foraging in the intertidal zone along our shorelines. These clever birds not only find places to hide their food like clams and cockles to enjoy later, but they are also able to remember where they have hidden them! Crows love walnuts, and can be seen dropping them on to hard surfaces to crack them open. Mayne Island crows have shown no signs of dependence on human garbage as a food source, unlike their city cousins and our local ravens who have discovered good things in our black plastic bags. Ravens on Mayne will tear apart bagged garbage left in the open. Ravens are territorial birds who often work in pairs to raid coastal seabird colonies and songbird nests, and they also prey on the chicks of farm birds. They will distract the adult birds while stealing the chicks, and ravens have even be seen attacking new-born lambs.
Here on Mayne Island, Michael Dunn has made the following observations about the two species. The winter population of crows fluctuates far more than that of ravens, and our crow flocks are mostly located in and around Village Bay and Miners Bay, and in the agricultural areas on the island. Pairs and family groups of ravens are often seen along Navy Channel, Gallagher Bay, Piggott Bay and Horton Bay, plus the forested areas of SW Mayne Island where at least two pairs of ravens have nest sites. Michael has also noticed that crows prefer habitats fragmented by humans, whereas ravens prefer more forest and less human disturbance. The two species do overlap in intertidal and agricultural areas. It appears that crows do not breed here on Mayne as there have been no observations of fledglings, only juveniles. Most Mayne Islanders, however, are very aware of the newly-fledged local ravens as they shriek and call their way overhead during late spring and early summer.
Dr. Freeman and his colleague, Eliot Miller, from the Cornell Lab of Ornithology, analysed over 2000 eBird accounts of aggression between crows and ravens across North America. (eBird is an online database used by many citizen scientists). Ben acknowledges that although citizen science can have its drawbacks, it has been an invaluable tool in his research on these birds. He has seen that bigger birds like ravens do not always dominate smaller ones like crows, and most of the time fights between the species are initiated by bands of crows. Ben is also investigating whether the actions of mobs of crows defending their nesting and foraging territory might actually prevent ravens from being able to populate crow-dominated areas.
For further reading on Dr Freeman’s work and on the topic of crows and ravens, please see below.