Animal behavior: synthesis of theoretical relevance and empirical findings

Animal Behavior

Interspecies Enemy Identification Depends on Facial Recognition

The formation of social groups is believed to confer a survival advantage to individual members of the group (reviewed by Marzluff, Walls, Cornell, Withey, and Craig, 2010). For humans, these advantages include the sharing of resources, information, skills, and childrearing tasks. Social groups are not limited to humans, but are also evident in species as diverse as ants, yellowfin tuna, and coyotes. However, our understanding of interspecies social interactions and the potential survival advantages that they confer are not understood to the same degree.

Domesticated animals, like dogs and cats, can readily distinguish friend or foe based on past interactions. Non-domesticated animals like the American crow (Corvus brachyrhynchos) seems to have the same capability. To better understand the parameters of 'enemy' recognition in crows, a group of researchers at the University of Washington in Seattle studied this phenomenon during a trap and release encounter. Essentially, Marzluff and colleagues (2010) proposed that crows remembered the faces of the people who trapped them as the enemy.

Methods

The researchers who trapped the crows wore masks (independent variable) (Marzluff, Walls, Cornell, Withey, and Craig, 2010, 700-702). Being captured was interpreted by the crows as an adverse experience. The association between the mask and the adverse experience was tested, by researchers walking through the crow territories after they had been released. The main dependent variables measured were scolding, following, and mobbing.

Results

A Mask worn during trapping (enemy mask) elicited a significantly stronger scolding response than masks not worn during trapping (neutral masks) (Marzluff, Walls, Cornell, Withey, and Craig, 2010, 702). In addition, enemy masks had no effect on crows that had never been trapped. The variable 'no mask' had no effect, as long as the person was not present during trapping. In addition, a hat worn during trapping was capable of eliciting a significant modest scolding response, but not a red arm band.

One of the more surprising results was that the scolding response increased over a period of almost 3 years in terms of the number of crows involved (Marzluff, Walls, Cornell, Withey, and Craig, 2010, 703). This result suggests that crows within a social group were learning to recognize an enemy as a group, based on the adverse experience of one or a few members.

Another variable tested was location, in terms of urban, suburban, and 'naive to trapping' activities ((Marzluff, Walls, Cornell, Withey, and Craig, 2010, 704-705). Although scolding occurred independently of whether the crows were presented with an enemy or neutral mask, the enemy mask far outstripped the neutral mask in how effective it was in eliciting mobbing in all locations. This finding suggests enemy recognition is not location dependent.

When crow reactions were broken down into no response, looking at person, scolding, and scolding and following, the enemy mask generated significantly more of the latter two responses (Marzluff, Walls, Cornell, Withey, and Craig, 2010, 705). In addition, when previously trapped crows encountered enemy and neutral masks at the same time, the scolding response invariably focused on the enemy mask.