Spatial and temporal winter territory use and behavioral responses of whooping cranes to human activities

Abstract

I investigated spatial and temporal winter behavior and behavioral responses of 5 territorial whooping crane families to human activities at Aransas National Wildlife Refuge during winters 2003-2004 and 2004-2005. Adult and juvenile cranes spent the majority of the day foraging (63% and 66%, respectively). Alert behavior comprised 15% of the cranes' time-activity budgets; preening or resting, and movement each constituted approximately 7% of the time-activity budget. Adults were more alert than juveniles in Jan-Feb. The proportion of time spent in other behaviors did not differ by age. Over-winter use of territories varied spatially and temporally. Flight occurrence was highest in Nov-Dec, coinciding with establishment of territorial boundaries upon arrival at the wintering grounds. Movement velocity (meters traveled/min) also tended to be highest in Nov-Dec, which may be due to territorial defense and foraging activities. Use of land, open water, and edge habitats (land and water interface) within territories appeared to fluctuate with primary food item availability. Disproportionate use of land habitat by several crane families coincided with peak production of wolfberry (Lycium carolinianum) fruit, which occurs in Nov-Dec. Edge habitat was used disproportionately to its availability throughout the winter, most likely because this habitat type provided refuge for blue crabs (Callinectes sapidus), an important food item for whooping cranes. Several families also used open water disproportionately to its availability. Behavioral responses of whooping cranes to human activities were limited. Responses to varying frequency and intensity of human stimuli were evaluated. Most stimuli did not elicit a response. Two crane families decreased the proportion of time spent foraging during periods of high-intensity stimuli; one family increased movement during such times. Foraging behavior of one family was significantly higher when stimuli frequency was high; alert behavior significantly declined as stimuli frequency increased. The mixed responses of territorial families to varying levels of human stimuli paired with the overall high level of reproductive success of the entire population led to my conclusion that current levels of human activities are not having a detrimental impact on the Aransas-Wood Buffalo whooping crane population.