4.1 Breeding oystercatchers
In a coastal area in the Netherlands, researchers studied the breeding success of oystercatchers which nest in territories on saltmarsh adjacent to the mudflats on which they feed and those which have territories further inland and are thus further away from their feeding grounds. Oystercatchers vigorously defend breeding territories on the saltmarsh; what do these results tell us about the value of territories?
The figure shows the number of successfully fledged young birds against the day on which the first clutch of eggs was completed (ie all the eggs had been laid).
Source: Ens et al. 1992. Journal of Animal Ecology, 61: 703-715.
Figure 3a reproduced with the permission of John Wiley & Sons.
©1992 The Author. Journal of Applied Ecology © 1992 British Ecological Society.
Model answer:
Inland-nesting oystercatchers have to fly to mudflats to collect food for their young. In contrast, salt-marshing nesting oystercatchers have territories adjacent to the feeding ground and thus have less far to move between nest and the saltmarsh. These salt-marsh nesters have a greater success when fledging young than the inland nesters. This suggests that territories adjacent to the saltmarsh are better than those further away. It is therefore likely that these territories are at a premium and held by dominant birds. Sub-optimal territories on the inland sites are probably held by subordinate birds; these may be younger or less experienced at challenging for and defending territory.
