Aggression and boldness in Merriam's kangaroo rat: an urban-tolerant species?

Urban development can fragment and degrade habitat, and such habitat alterations can have profound impacts on wildlife behavior. In urban areas, individuals may occur closer to each other and experience high levels of disturbance, which may favor increased aggression and boldness in urban-dwelling wildlife. We investigated the influence of urbanization on aggression and boldness and the relationships between these traits in Merriam's kangaroo rat (Dipodomys merriami). We predicted that Merriam's kangaroo rats living in urban areas would be more aggressive and bolder than Merriam's kangaroo rats in wildland areas, that the 2 traits would be positively associated, and that the association would be stronger in urban areas. We livetrapped Merriam's kangaroo rats at 4 urban and 4 wildland sites in and around Las Cruces, New Mexico, United States, and assessed aggression using a mirror-image stimulation test and boldness using a predator-scent exposure. We found no difference between urban and wildland Merriam's kangaroo rats in either aggression or boldness. We found a positive statistical relationship between aggression and boldness, but this relationship was not affected by urban versus wildland habitat. These results indicate that Merriam's kangaroo rats may be tolerant of urbanization, if habitat patches within urban areas are similar to wildland habitats.