tied to home | 93to her subjects, she discovered that the further the birds went from the
Skomer colony during incubation and chick- rearing, the stronger was
the evidence that they encountered good feeding patches.^9 One, but by
no means the only explanation, is that the good patches close to Skomer
had been exhausted.
Northern Gannets have incubation stints of a similar duration to
Razorbills and guillemots. Gannet enthusiast Bryan Nelson recorded
that the average length of time for which a male British gannet sat was
36 hours as compared to 30 hours for a female.^10 That allows time for the
gannets to fan out from the colony, but little more. These gannet spells
are short compared to the shift lengths of Red- footed Boobies, which
average some 60– 70 hours. This contrast is no surprise since breeding
gannets are surrounded by the productive fish- rich summer seas of north-
ern temperate latitudes. In contrast, Red- footed Boobies are tropical.
They are light; witness their ability to nest in trees unlike most ground-
nesting gannets and boobies. They can fly at comparatively low cost
across barren tropical seas, probably ranging up to 150 km from the
colony until they encounter small fish driven to the surface by, for ex-
ample, hunting tuna. Then their agility comes to the fore. Not only do
they dive into the sea like other boobies; they are also able to snatch
flying fish at the sea surface or even catch them in mid- air.
This has not been a comprehensive survey. Rather it is a brief hors
d’oeuvre in the build- up to the two groups of seabirds where incubation
stints can be seriously long, the penguins and the petrels. Here the sit-
ting bird can remain incubating ashore for a few weeks and its partner
has time enough to wander thousands of kilometres. But does it avail
itself of that time to travel great distances, or does it simply meander
in the vicinity of the colony until it has gained sufficient weight for a
lengthy spell of incubation, at which point it sets a homeward course?
Today’s tracking devices have the potential to reveal the answers.
Among the petrels and albatrosses, there is a weak correlation be-
tween size and length of incubation stint. With larger body reserves, the
larger species can sit for longer. Average shifts of small storm petrels
(2– 5 days) and diving petrels (1– 2) days are only moderate. Nonetheless
one species, Leach’s Storm Petrel breeding on Country Island off Nova
Scotia, deserves a special mention. Thanks to geolocator information,