Visitors in a zoo environment have the potential to impact the animals that they are viewing in a variety of ways. Recently, there have been suggestions that free-range enclosures, where visitors can walk directly through an animal's exhibit, may reduce the potential for negative visitor impacts. The aim of this study was to examine associations between visitor numbers and noise levels and enclosure use and the stress and critical behavior of 24 bird species housed in a free-flight, mixed species aviary. Using GIS (Geographic Information Systems), the locations of the birds were marked on a digital map of the aviary, with their behavior and vertical distance above the ground also marked. In addition, visitor numbers and noise levels were simultaneously monitored using scan sampling. Thirty-minute intervals were used to collect bird data, while 10-minute intervals were used to collect the visitor data. Under periods of high visitor numbers, several changes in how the birds used their enclosure space were observed, including; movement away from the visitor pathway, decreased range sizes and increased use of vegetation cover. However, the lack of association between visitor numbers and the performance of stress related (pacing, aggression), and critical behavior (feeding, resting, nesting), suggest that the birds were not experiencing substantial negative welfare consequences. Instead, the ways in which the birds used the space in their free-range enclosure appears to have minimized any potential negative effects during high visitor periods.