adUlt migrations | 75mars behind a trawler, or a gull with hours to wait before it can join the
gull melee to open the next batch of garbage bags delivered to the rub-
bish tip.
In fact there are at least two key factors that may influence how a
seabird’s daily schedule outside the breeding season might differ from
that during breeding. The first is that it is the period when most species
moult. They normally do not moult during breeding, and instead grow
the next year’s brand new set of feathers outside the breeding season.
Very likely this is because the moult is energetically demanding. As is
true of all penguins, Macaroni and Rockhopper Penguins remain ashore
during the moult period. They look thoroughly dejected as the old feath-
ers, pushed out by the growing fresh feathers, flutter over the colony
that acquires the look of a down duvet apocalypse zone. The penguins’
daily energy expenditure during this time is about 40 percent higher
than during incubation.^31
For species which undertake a long post- breeding migration, moult
generally occurs after the journey. The reason is clear. While the princi-
pal wing feathers are being shed and re- grown, the seabird’s flying abil-
ity is potentially reduced. For most species, where only a few feathers
are shed at a time, flight may be impaired but not lost. For larger auks,
whose small wings relative to body size render flight taxing at the best
of times, moult may be a period of flightlessness. Indeed if several wing
feathers are moulted at once, the hazardous process may be completed
more quickly than if they adopted the more normal sequential strategy
of other birds.
The second factor likely to influence seabird activity outside the
breeding season is that birds are then freed of the requirement to shut-
tle back and forth between colony and feeding area. This may be a rela-
tively trivial factor for, say, a gull or cormorant that is feeding close to
its colony when breeding, and feeding close to an onshore roosting site
in winter. It could be far more significant for a petrel whose breeding
season responsibilities include flying several hundred kilometres every
day. Indeed the prudent petrel might reach a non- breeding sea area with
adequate food and, in the vernacular, ‘chill out’, flying only as far as
required to meet its much- reduced daily energy needs. Presumably this
switch to a life of relative inactivity would be even more pronounced if