Ferruginous Hawk (Buteo regalis) responses to human disturbance during the breeding season

The expansion of the human footprint across the world is increasing the number of interactions between humans and wildlife. Many studies have quantified wildlife behavioural responses to humans, as this is an active area of research with practical implications for species conservation. Animal behaviour may be influenced by the properties of the human disturbance itself, the environment in which the interaction occurs, and the individual's past experience, but these potentially important factors have rarely been evaluated. Furthermore, it is unclear how individuals behave through time after a human disturbance. In southern Alberta and Saskatchewan, I quantified flight initiation from the nest by Ferruginous Hawks (Buteo regalis) in response to approaching investigators and used digital video systems to quantify their behaviour following investigator departure. In Chapter 2 I studied the flight initiation distance (FID), the distance at which flight is initiated from the nest in response to an approaching threat, by adult Ferruginous Hawks. We used FID to quantify the relative probability of flight during a given approach. Probability of flight was related to the type of approach by investigators, the anthropogenic landscape around the nest, and the number of previous visits by investigators. Approaches by humans on foot resulted in a greater probability of flight than those in a vehicle. Approaches while driving on private access roads, which are roads used infrequently by vehicles, were associated with increased probability of flight relative to other road types. Probability of flight was negatively related to an index for the number of vehicles passing near the nest, and increased as the number of previous investigator approaches to the nest increased. Chapter 2 highlights the dynamic and complex nature of the decision to initiate flight from the nest and provides insight as to why probability of flight varies within a species. Having explored factors influencing the Ferruginous Hawk's decision to initiate flight in response to human disturbance in Chapter 2, Chapter 3 focused on the behavioural consequence through time after being disturbed by humans. Here, I used digital video footage of Ferruginous Hawk nests to document behaviour at the nest of adult males and females up to 12 hrs following an investigator disturbance, and test two non-exclusive hypotheses that may explain differences in behaviour relative to undisturbed control periods. On average, across the 12-hr sample period, female Ferruginous Hawks spent significantly less time on the nest following investigator disturbance compared to controls, but individual variation was high. Delivery of prey items to the nest was not significantly different between disturbed and control sample periods for the same nests. Time on nest was initially lower for disturbed females than for controls but became more similar over the span of the 12-hr sample. Age of nestlings and number of nestlings were important, as female time on the nest returned to control-levels more quickly for individuals with young nestlings or larger broods. Thus, I found support for both the harm-to-offspring and reproductive value hypotheses. This was among the first studies to identify that disturbed animals demonstrate behavioural differences up to 12 hrs following disturbance. The ability to adjust flight initiation behaviour in response to types of human approaches and the consistent delivery of prey when disturbed suggested that Ferruginous Hawks nesting in the highly anthropogenic regions of southern Alberta and Saskatchewan demonstrated the behaviours that should allow them to coexist with some human disturbance at the nest site. However, I also found instances of Ferruginous Hawk flight initiation at large distances, and that some individuals reduced time on nest for lengthy durations following a human disturbance. Understanding how these extreme behaviours relate to reproductive success of Ferruginous Hawks is likely essential to understanding human impacts on the population in Canada. My research was intended to contribute to the ongoing conservation effort for this species, and I discuss potential implications for management in Chapter 4. I suggest that management policies should vary the size of protective setbacks according to the apparent degree of sensitivity of adults during different nesting stages and for different types of disturbance. For example, after nearly all clutches have hatched (by mid-June), 500-m setbacks should effectively prevent Ferruginous Hawks from being disturbed by low-level disturbances, such as passing vehicles.

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