- In order to examine the potential impact of military jet overflights and other disturbances on productivity of peregrine falcons (Falco peregrinus), we observed behavioral reactions of peregrines to disturbances at nests along the Tanana River, Alaska during the 1995-1997 breeding seasons. Military jets conducted low-altitude flights over a sample of nests under observation in each year (experimental nests), while other nests were not intentionally overflown (reference nests). Other disturbances occurred at random. Animal noise monitors (ANMs), which collect and store data on noise disturbance levels, were deployed at each observed nest. A total of 878 above-threshold (≥ 85 dB) overflights were recorded by the ANMs during the course of the study. A total of 401 close (defined as ≤ 1000 m slant distance from the nest) overflights by subsonic F-16, F-15, A-10, Harrier, Jaguar, or Tornado jet aircraft were recorded during observations. Close overflights by military jets accounted for 63% of all observed potential disturbances at experimental nests; they accounted for 2.6% of all observed potential disturbances at reference nests. Other potential disturbances at reference nests included civilian fixed-wing aircraft (41%), boats (33%), avian predators (17%),
helicopters (5%), and mammalian predators (1%). Peregrine falcons responded
differently to animate and inanimate sources of disturbance, and responded most intensely
and most frequently to other raptors, particularly conspecifics. Flight reactions were common, but not in response to inanimate sources. Among inanimate potential disturbances, falcons responded most intensely to boats (6% of reactions involved flight), and least intensely to helicopters (3%) and fixed-wing aircraft (2%). Intensity of reactions to military jets was indistinguishable from that to either boats or other aircraft. Intense behavioral responses (including flight reactions) to military jet overflights were rarely observed in this study, even at slant distances <500 m, and no intense behavioral responses were observed at slant distances >550 m. Peregrine falcon productivity (number of fledglings produced per nesting attempt) in the study area was within the normal range for Interior Alaska and the Tanana River. Dose of jet aircraft disturbance was not correlated with productivity. Productivity was, however, negatively correlated with reactivity of both individual falcons and mated pairs. Those falcons that responded more intensely to overflights tended to have lower productivity. The sensitivity of
breeding peregrine falcons to low-altitude jet overflights is a better indicator of subsequent productivity than actual dose of overflights. This is likely a reflection of lower parental quality/investment among breeding pairs with high reactivity (i.e., younger, less experienced parents are less likely to be productive).