Many studies on the effects of human disturbance on birds have focused on adults and report mainly negative effects. Few focus on effects on chicks. Here, an experimental approach was used to determine effects of human disturbance on chick growth. Cassin's Auklet chicks were assigned to one of three groups (control, low and high disturbance). In experimental groups, a person walked close to the burrow entrance four times or eight times a day, according to the disturbance level assigned. Growth (mass increment and wing length increase) was measured and compared between the three groups. Since adults are absent from the nest during the day, chicks, but not their parents, experienced the disturbance regime. Body condition and experience (age) of the parents did not influence peak or fledging mass of chicks subject to disturbance. Chicks were not affected by disturbance in the early stages of growth, while chicks in the experimental groups stopped gaining weight sooner than controls and fledged at lower weights (6 to 9% less) compared to chicks in the control group. Chicks in the high disturbance group had a lower peak (F2,68 = 7.53, P < 0.001) and fledging mass (F2,68 = 17.274, P < 0.001) compared to chicks in the control group, while chicks in the low disturbance group had a lower fledging mass (F2,68 = 17.274, P < 0.001) but similar peak mass. As subsequent survival of chicks is likely to be affected by their mass at fledging, the results show that it is necessary to consider the chick growth stage when making management plans for areas with burrow-nesting seabirds.
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Vol. 32 • No. 4