tied to home | 107the colony. Compared to their elders, the immatures have less knowl-
edge of prime feeding areas, but perhaps have more ‘spare’ time to learn
the whereabouts of those areas. This line of thinking matches the find-
ing (Chapter 7) that adults are the more consistent in their use of a
particular feeding area.
A persistent message from this chapter has been that birds tend to
forage further from the colony during incubation than chick- rearing. If
colonies tend to be spaced apart – as is the case – that would automati-
cally lead to birds from different colonies experiencing less overlap of
foraging areas during chick- rearing. Over three breeding seasons, the
OxNav group studied Manx Shearwaters on Skomer Island, at the south-
ern margin of the Irish Sea, and on Copeland Island, off Belfast, just
over 300 km to the north.^31 GPS tracking revealed much overlap during
the incubation period in a rich feeding area, the Irish Sea Front, south-
west of the Isle of Man, and much closer to Copeland than to Skomer.
Overlap was reduced during chick- rearing when birds were feeding
closer to home.
In other species, there is more pronounced mingling between the
birds from neighbouring colonies. An example is described in a paper
with the give- away title ‘Social foraging European shags: GPS tracking
reveals birds from neighbouring colonies have shared foraging grounds’.^32
Since the three colonies studied, in the Scilly Isles, south- west England,
were separated by short distances, only 4– 10 km, there was probably
opportunity for the birds from different colonies to share information
about where to feed. Nevertheless the shags, not the best fliers, did most
of their foraging within 3 km of home, rather than in shared seas.
If birds of the same species from different colonies tend to avoid
sharing feeding areas, it is intriguing to ponder whether or not birds of
different species sharing the same breeding station share feeding niches.
Classical ecological theory would suggest that there is likely to be some
segregation of feeding niches. For example, one species may feed deeper
underwater or further from the colony than another, or may simply
catch different food. That said, the interspecific differences generated
by competition may be slight compared to the differences in feeding
routine that I have described for different stages of a species’ breeding
cycle.