Ja. Vickery et Mdl. Brooke, THE KLEPTOPARASITIC INTERACTIONS BETWEEN GREAT FRIGATEBIRDS AND MASKED BOOBIES ON HENDERSON-ISLAND, SOUTH-PACIFIC, The Condor, 96(2), 1994, pp. 331-340
Kleptoparasitic activities by Great Frigatebirds (Fregata minor) on Ma
sked Boobies (Sula dactylatra) were quantified on Henderson Island in
the South Pacific. The frequency of kleptoparasitic attacks increased
towards dusk, the time when most Masked Boobies returned to the roost
site. Masked Boobies returning to the roost low (< 30 m) over the wate
r were significantly more likely to be chased than those returning at
a higher altitude. Single boobies were also significantly more likely
to be attacked than boobies returning as one of a group of birds. Howe
ver, group size and height were positively correlated. There was no ef
fect of group size on the likelihood of attack. Sixteen percent of cha
ses were successful and the success rate was not influenced by either
the height or the distance of the target from the roost. The duration
of the chase was, however, influenced by the position of the target: c
hases on distant or high targets lasted significantly longer than chas
es on targets that were low or close to the roost. In addition success
ful chases were significantly longer than unsuccessful ones. We discus
s these results in relation to the chase tactics of frigatebirds, the
avoidance tactics of boobies and the energetic costs and benefits of k
leptoparasitism. Approximately 40% of daily energy expenditure of some
individual Great Frigatebirds may be secured through kleptoparasitism
. However, on average, frigatebirds may be meeting under five percent
of their daily energy demands by this feeding method.