Far From Land The Mysterious Lives of Seabirds

90 | Chapter 5

which partly arises because females spend more time sitting on the

water in darkness. Why there should be this consistent difference among

gadfly petrels, with males travelling further than females during the

pre- laying exodus, remains something of a mystery. Perhaps it benefits

females to minimize the distance that needs to be flown when they are

laden with a nearly fully- formed egg.

***

With eggs to incubate and then chicks to tend, parent seabirds are sig-

nificantly tied to one spot, the colony. They need to return there more

or less regularly, otherwise the breeding attempt will founder. This con-

straint, this leash to home, inevitably restricts the journeys that can be

made during the breeding season. It also makes the case for positioning

Two distinct areas are used by Barau’s Petrels during their pre- laying exodus

from the Reunion colony, one off the African coast, the other south- east of

Madagascar. The former is mostly used by males, the latter by females. Shading

intensity corresponds to intensity of use by the birds. Depth contours (metres) show

the birds are mostly using sea areas where the depth is greater than a kilometre.

Reproduced with permission from Elsevier, from the work cited in Note 6, Chapter 5.

0°S

10°S

20°S

20°E 40°E 60°E

–4000

–4000

–4000

-^4000

–4000

–4000

–4000

–4000

–300 0 –30

Reunion^00

Island

Reunion

Island

80°E 100°E

Kernel density

contour

80%

60%

40%

20%

Colony

30°S

40°S