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Wednesday, March 9, 2016

Corvid Course - Class #5 The Study of Crows

Our 2016 "Conservation Course" started January 25th.  Below are short-hand notes taken by Raechel Youngberg and a video by CJ Peterson, both class participants.  See notes and videos from the previous classes here:
first class
second class 
third class
fourth class

Class #5 - The Study of Crows with Kaeli Swift & Loma Pendergraft
February 22, 2016 

 Watch and listen to the entire class on this video

Crows, as we have discussed in previous classes, are socially monogamous but can have multiple sexual partners. Crows form a tight pair bond that generally lasts for life. The average crow lifespan in the wild is 15-17 years but captive crows have been documented to live up to 30 years of age.

Crows take part in a unique rearing style called cooperative breeding. A mated pair may be assisted in raising a chick by a previous son/daughter or sometimes an unrelated crow. This breeding style has not been proven to assist the mated pair that much but studies have shown that it is beneficial during low resource years.

Crows are social animals and commonly roost together. This practice is called communal roosting. Seattle area crows have been documented to roost together at UW-Bothell campus. Scientists have some theories as to why this practice may occur. One theory is that roosting together protects individuals from predation by cats, red-tailed hawks and coopers hawks. Scientists also believe that crows may exchange information with each other at these roost sites.
As discussed in prior classes crows are highly intelligent animals and have a well-documented use of tools. The New Caledonia Crow has been documented to make two types of tools. Crows display the following attributes of intelligence: causal reasoning, flexibility, imagination and prosecution.

While crows excel at intelligence tests that demonstrate cause and effect knowledge, one study showed that crows struggle with counter-intuitive tests that require inference.

Crows are one of twenty-five species to have been documented demonstrating play behavior. Scientists once thought that animals played to prepare themselves for survival in the wild. However a recent study took one group of animals that did not play during development and measured their fitness against a group of animals that did play during development. There were no significant changes between the two groups. Play during development is now thought to help animals cope with stress better throughout their life. 

The Avian Conservation Lab run by John Marzluff at University of
John Marzluff with a crow
Washington has been trapping and banding crows since 1997.  In one study, researchers wear a caveman mask and hat while trapping the crows. The researchers then test the bird’s reaction to the caveman mask, a "neutral" Dick Cheney mask, the hat without the caveman mask, and an unmasked participant. When crows that have been trapped are exposed to the caveman mask they participate in scolding and mobbing behaviors towards the researcher. Mobbing is when groups of crows attack or harass a potential predator. Scolding behavior refers to a specific call the crows make when they feel threatened.

Additional studies by the Marzluff Lab have demonstrated that crows can recognize faces that have fed them or that have hurt them in the past. Crows do not seem to forget this knowledge and they pass this information onto other crows, including their young. The Marzluff Lab researchers have been mobbed and scolded by more crows than their study has caught. A sign that captured crows are teaching other crows that the caveman mask and hat combination signifies a potential threat.  

Crows mobbing a red-tailed hawk
Mobbing is costly and can be dangerous for the crow. Crows only use this tactic when they deem the predator worth the risk. One study sought to learn more about this behavior. An osprey is as big as a hawk but it eats fish so it poses little to no risk to crows. Crows rarely mob osprey - however in areas where encounters between osprey and crows are uncommon (crows don't know what osprey are) the rate that crows mob osprey is higher. In areas where osprey and crow encounter are common mobbing rates are lower. When crows do mob osprey it is generally the younger naive crows that do so. The older experienced crows recognize that an osprey poses no threat and will not participate in mobbing events against osprey. This is yet another example of crows using mobbing events to teach potential threats to younger or naive crows.

One study sought to find out if crows felt threatened by a researchers gaze (eye contact) or their expression. Studies were conducted to see how close a researcher could get while either staring at the crow or making an expression. Then an observer would note how close the researcher got before the crow reacted (flew off, looked at the person etc). The study found that crows flew away more often when a researcher was walking towards the animal while staring at it. Eye contact is considered a threat because it is a sign of potential predation whereas facial expressions can be faked and are not reliable.


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