Class #3 - The Biology, Behavior and Brains of Ravens with Dana Visalli
February 8, 2016
Watch and listen to the entire class on this video
Corvids are in the passerine family, which contains more than half of all bird species. The passerines are often thought of as "song birds," but their common characteristic is really that they are "perching" birds. All passerines have two toes that point forward and one toe that points backwards which helps them perch.
How to identify a raven versus a crow:
-Crows have straight tail feathers that may appear to be cut.
-Crows have a smaller body than ravens.
-Crows have a smaller beak than ravens.
-Crows generally travel in flocks whereas ravens travel alone or in pairs unless there is food around.
-Crows are rarely found in the Methow during the winter.
Raven-Ravens have a very big bill.
-The tips of ravens "primary" wing feathers are spread out like fingers, similar to eagles and vultures (reduced drag when soaring, which is something ravens do and crows not so much)
-Ravens have a wedge/fan shaped tail.
-Ravens are noisy fliers due to the air displaced by their wings.
-Ravens have large neck feathers that can be puffed out in a similar way to a grouse to communicate social rank and dominance.
- Ravens are widespread throughout the Northern Hemisphere.
Ravens are highly adaptable and intelligent animals and these traits have helped them adapt to a variety of different environments. The Common Raven (Corvus corax) can survive in deserts, rainforests, and mountainous regions.
Ravens average lifespan is 15-20 years, but in captivity they have been know to live until 40 years of age. They are one of the largest passerine birds and can weigh 2-4lbs. The Thick-billed Raven (Corvus cassirostris) from the Horn of Africa is the largest raven species and can weigh up to 6lbs.
It is very difficult to distinguish if a raven is male or female unless you see them right next to each other. Males are slightly larger than females. Females can be identified without a male present for comparison by a unique knocking call that is specific to females. Both males and females have expressive neck feathers that they use to communicate dominance. They will puff their neck feathers and legs feathers out to appear larger and more dominant.
There have been many studies on the intelligence of ravens and other corvids, especially their use of tools and problem solving skills.
Caledonia Crows display the most elaborate tool use of any corvid. Caledonia crows use two types of tools. The first tool they make is a stick with a hook strategically broken off at the end so they can probe insects out of holes. For the second tool they find a specific leaf that features barbed edges that they then roll into a spear shape. The second tool takes multiple steps and demonstrates causal reasoning (they see the relationship between a cause and its effect).
Corvids have the largest brain size to brain stem ratio of any bird species (excluding parrots). The European magpie has demonstrated self-awareness in several studies. In one study, scientists placed a small yellow dot underneath the beak of the magpie where it could not see it. Then the birds were placed in front of mirrors. The birds quickly realized that they were looking at a reflection of themselves and would then scratch off the yellow dot.
Many studies have been done on the problem solving abilities of ravens. In several studies, scientists placed a piece of meat on a string and then tied it to a branch. This would never occur naturally in the wild and thus was a unique experience to which they have not previously been exposed. The ravens quickly realized they could use their foot and beak to pull up the string, hold it with their food, then pull it some more, continually holding it down until they have the meat.
Scrub jays demonstrate brain flexibility and prospection while caching food for the winter. Scrub jays cache perishable and non-perisable food items and are able to retrieve around 75% of their caches after 6 months. The jays not only remember where they stored the food but how long it will last before rotting, and go for the perishable food first.
Ravens mate for life and are socially monogamous. Pairs build nests together and raise their young together. Ravens frequently start incubating eggs before all the eggs have been laid. The last egg to be laid therefore has a shorter incubation period and is smaller and weaker. This is believed to be a backup food source for the other young when times between meals are scarce.
Ravens interestingly enough cannot tell the difference between their own eggs and another bird's eggs. Well-known raven biologist and author Bernd Heinrich individually placed a chicken egg, a plastic easter egg, and film canister filled with water in a ravens nest. The ravens incubated the chicken and the plastic easter egg but did at least toss out the film canister. Ravens are fierce guards of their nest and in the wild it is unlikely that another creature would be able to sneak an egg into a ravens nest (like many birds do with "brood parasitism"), so ravens never had to develop ways to distinguish their eggs.
Ravens are omnivores but sometimes demonstrate meal phobia (often called neophobia). They are wary around unknown carrion sites and often wait for the presence of crows, magpies or large carnivores before approaching novel carcasses.
Ravens and wolves have a very interesting relationship. A study in Yellowstone tracked the number of ravens found on wolf kills versus hunter kills. On every single wolf kill the scientists discovered ravens but they never found ravens on the kill sites of human hunters. Ravens listen for wolf howls that signal the beginning of a hunt and this relationship may benefit both species. Ravens are more alert to their surroundings than wolves and may act as a early warning system for danger for wolves.
It seems that the local Methow population of ravens has been on the rise. This could be linked to human inhabitants building roads and clearing snow which allowed more deer to inhabit the valley and survive better during the winter. Deer carcasses are a common food for corvids during the winter.