By Quinn Rider, BVAC Retail Manager, B.S. Ecology, Behavior, and Evolution
It’s spring in Bear Valley. The sun is out, the snow is melting, and the birds are chirping. However, you may notice one of our frequent winter visitors has been strangely silent. Common Ravens, Corvus corax, are a frequent and charismatic visitor to our neck of the woods, at least in the winter. Ravens, the largest and most intelligent of the corvid family, consume carrion, small vertebrates, nuts, seeds, and berries (7). They are also frequent consumers of anthropogenic garbage, a food source that has driven a massive expansion of their range and population (1).
Ravens didn’t arrive in Yosemite Valley until the 1960s when human traffic picked up substantially in the area, though they were somewhat common throughout the lower reaches of the Sierra Nevada Range (7). Increasing traffic to the park provided a new food source for both ravens and bears. While Yosemite introduced multiple measures to decrease conflicts between humans and bears like implementing bear boxes, such improvements had little effect on the ravens who underwent a population explosion between 1960 and 1980, cementing their residence in the valley (1). This is likely around when ravens arrived in Bear Valley as well. Food scarcity during the harsh winters had previously kept ravens rare in the higher elevations of the Sierra (7). The opening of the ski resort in 1967 and the subsequent traffic it brought to town would have increased food subsidies available to ravens in the winter, providing them enough food to survive through the snowy winter months. However, no documentation exists on the subject of ravens in Bear. A study in the early 2000s found that ravens were absent from the Badger Pass ski area throughout the summer. However, they descended upon the resort in droves the morning after opening day, the first morning of the season during which trash was available for scavenging (1). The same seems to be true in town, as the raven population has noticeably declined since the closure of our winter facilities. However, food may not be the only thing on their mind during their visits to Bear.
If you watch the less-trafficked slopes up at Bear Valley Mountain Resort carefully enough, you may see ravens dunking themselves in the snow, sliding or rolling down slopes (2), and even using bits of plastic to sled downhill before flying to the top and beginning again (5). The scientific community posits that ravens use play to demonstrate their intelligence and athletic prowess to potential mates (2).
Ravens are moderately social as far as corvids go, interacting both with other ravens and conspecifics, both human and non-human. The development of intelligence in avians is credited to their complex social relationships both between flocks and monogamous breeding pairs for those species that form them. While ravens are not the most social of avians, it is likely their monogamous pairs to which they owe their impressive intelligence. This relationship is theorized to be the most complex relationship avians form. Sexually immature and single ravens are more prone to forming groups than adult pairs, though the pairs may join groups outside of the breeding season (3).
Group formation facilitates scavenging for large carrion. Carrion is an especially important food source in the winter months. However, ravens don’t possess sharp enough beaks to open the hides of carrion on their own, making them reliant on other scavengers to access the majority of a carcass. Thus, they take and offer cues to and from conspecifics, members of other species. They track wolves on their hunts, either by calls, tracks, or visually (6). While they haven’t been shown to track coyotes as strongly, research has demonstrated that ravens associate with coyotes during scavenging, along with red tailed hawks. Ravens circling will draw in hawks that will open the carcass for them. However, they will never associate with or feed near big cats, the risk of becoming a meal themselves too high (4).
Far from harbingers of doom, ravens are social, playful, and intelligent. They are members of their ecological community that benefit from and aide their conspecifics, be it purposefully or not. Expansion of their territory and population has been driven by anthropogenic activity, allowing them access to even the higher reaches of the Sierra during peak tourism season. Perhaps they are more harbingers of the ski season, swooping in on frosted wings to consume that which we leave behind.
References
1. Brook, C., Bernstein, D., & Hadley, E. (2012). Human food subsidies and Common Raven occurrence in Yosemite National Park, California. Western Field Ornithologists, 44:127–134. https://doi.org/https://archive.westernfieldornithologists.org/archive/V44/WB-Brook-44(2).pdf
2. Brazil, M. (2002). Common Raven Corvus corax at play; records from Japan. Ornithological Science, 1: 150–152.
3. Bugnyar, T. (2016). Social cognition in ravens. Comparative Cognition & Behavior Reviews, 8:1–12. https://doi.org/10.55776/p29705
4. Orr, M.; Nelson, J.; Watson, J. (2019) Heterospecific information supports a foraging mutualism between corvids and raptors. Animal Behavior, 153:105-113.
5. “Raven uses plastic lid as sled || Viral Hog.” https://www.youtube.com/watch?v=Org1OG1bIN0
6. Stahler, D.; Heinrich, B.; Smith, D. (2002) Common ravens, Corvus corax, preferentially associate with grey wolves, Canis lupus, as a foraging strategy in winter. Animal Behavior, 64(2): 283-290.
7. Zeiner, D.C., W.F. Laudenslayer, Jr., K.E. Mayer, and M. White, eds. 1988-1990. California's Wildlife: Common Raven. California Depart. of Fish and Game, Sacramento, California, 1-3:353-354. California Depart. of Fish and Game, Sacramento, California.
