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English summary
The development in the size of the Arctic Tern population in West Greenland is difficult to assess due to insufficient data and fluctuating breeding numbers in the colonies between years. But the general picture is that the population has declined over the past 50 years. The archipelago Grønne Ejland in the southern part of Disko Bay is, apart from being the largest arctic tern colony in Greenland, the only locality where systematic counts of the tern population have been carried
out. The choice of Grønne Ejland as a study site for two month of fieldwork in 2002 seemed therefore appropriate.
Total numbers of breeding Arctic Terns in Greenland are estimated at at least 65,000 pairs.
The arctic tern population in 2002 on Grønne Ejland was estimated at 18,000 pairs, which is the highest number of breeding terns on the islands in several years. In 1946 population was roughly estimated at 100,000 pairs. This was probably a gross overestimate, and a revised 1946-estimate based upon information from 2002 would be about half of this figure. Even taking this reduction of the 1946-estimate into account, a significant decline since then in the arctic tern population
on Grønne Ejland is apparent.
The growth rate of the arctic tern chicks in 2002 was somewhat slower than found during similar studies elsewhere within the species range. Furthermore, the chick survival was low and these features may indicate shortage of food for the chicks.
In spite of the ban on harvesting of arctic tern eggs introduced with the new bird protection regulations, egg collection still took place on Grønne Ejland in 2002. However, the extent of the harvest in 2002 was estimated to be lower than recorded in 1996.
The results of the fieldwork revealed that the terns were able to replace a removed clutch. The chicks of the relaid eggs were slightly lighter but they showed no difference in growth and survival rate compared to chicks in non-manipulated nests. Relaying is probably a
normal reaction to predation or egg collection in Greenland, at least in years with favourable conditions in spring.
Harvest of tern eggs has been very intensive in W Greenland for decades, and despite legally regulated, the harvest has been practised almost uncontrolled. And the population decline is most likely mainly a result of this acticity.
The results of the 2002 field work indicated that food shortage may have played a role in the low productivity of the tern colony. If this is the case, food availability and hydrographic features may also be factors involved in the general decline in the W Greenland population.
There is, however, no data available to analyse how and to which extend food shortage could have contributed to the decline. Natural predators, such as foxes, will only affect local tern populations, and it is not likely that they are the cause of the general decline, as often maintained by the local inhabitants.
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