Figure 1.
Foraging trips of Guanay cormorants (left) and Peruvian boobies (right) tracked with GPS.
Left: four successive return trips of a Guanay cormorant (1–4). Right: three successive return trips of a Peruvian booby (1–3) and four successive tracks (A–D) of a second individual Peruvian booby (looping course A and C, return trip B and D). Arrows indicate the flight direction; dots indicate sitting on the water, small red circles the deep diving events, blue circles zones of area restricted search (ARS).
Figure 2.
Bearings taken by groups according to the centre of the island and difference in angle between the return bearing and the departure bearing of Guanay cormorants and Peruvian boobies.
Upper four figures: Bearing (in°) taken by groups according to the centre of the island and size of groups (from 10 to 10,000) of Guanay cormorants (black) and Peruvian boobies (white) leaving the island (▴) and returning to the island (▾). The circles indicate the bearings at departure and when returning taken by individuals tracked with GPS. Lower two figures: difference in angle between the return bearing and the departure bearing during the next foraging trip of individuals tracked with GPS.
Table 1.
Circular correlation coefficients between angles for Guanay cormorants and Peruvian boobies fitted with GPS.
Figure 3.
Movements of a Guanay cormorant in the vicinity of the colony and view from the sea of a compass raft.
(Left) Fine scale movements of a Guanay cormorant tracked by GPS at 1 sec interval in the vicinity of Isla Pescadores (in grey). Two successive foraging trips (1 and 2) from the nest (black circle). The location of the compass raft visited after departure from the colony is indicated by a circle (circle) and the arrows indicate flight direction. (Right) Photograph taken from the sea of a compass raft, with the colonies of seabirds on Isla Pescadores in the back ground.
Figure 4.
Changes in the bearings according to the centre of the island of the compass raft (circle) and of the departing (▴) and returning (▾) groups of Guanay cormorants during two consecutive days.
In some cases, when opposing arrows overlay, they appear as a star.
Figure 5.
View from the summit of the island showing part of a large aggregation of nesting guano birds on Isla Pescadores, with compass raft at sea.
The photograph shows part of the seabird aggregations dominated by Guanay cormorants (black plumage), with Peruvian boobies (white plumage) on the edge of the mains groups of cormorants.The black arrow indicates the location of the compass raft at sea.