Anthropogenic impacts to wildlife populations represent a reoccurring theme in wildlife management as the human population expands into wild landscapes. Our study focused on a great blue heron (Ardea herodias) colony of approximately 20 nests uniquely located along the Slate River near Crested Butte, Colorado. This high mountain stream increasingly draws river recreationists, especially stand-up paddle boarders. Our study assessed how human activities around the Slate River influenced heron behavior. We quantified human activities through one hour observations and heron responses through behavioral sampling. High hourly rates of human activities near the heronry coincided with brood rearing and fledging. Road traffic dominated all the types of human activity during all times of day and heron seasons; however, it only accounted for 0.004% of heron disturbances. In contrast, river recreation comprised less than 1% of all the activities in the valley, but accounted for 80-100% of heron disturbances. Our research showed that watercrafts floating directly under nesting great blue herons caused hunkering, alert, and flushing behaviors in over 80% of the herons at the colony. Of the 58 observed river recreation events, individual herons exhibited disturbance behaviors 388 times, and 57 herons flushed from the nest or surrounding wetland. During floating events, herons significantly decreased time spent in self-maintenance behaviors, their predominant undisturbed behavior. Foraging, nest maintenance, brooding, and agonistic behaviors ceased altogether during river recreation events. Floating event characteristics influenced the intensity of the heron response. Events that elicited more disturbance included larger groups (greater than three watercrafts), clustered groups floating through the colony with little separation between
watercrafts, groups with floaters standing upright on their boards, groups that produced noise, and groups that stopped underneath the colony. Our study demonstrates that river recreation can negatively impact great blue heron breeding and that spatial segregation between the birds and recreationists is required during the nesting season for effective species conservation.
