The breeding season

The Arctic Skuas start returning to their breeding grounds on Fair Isle in the third week of April. In the years 1973–75, the first Arctic Skua was seen on the island on 16 April. In 1976 the first bird was seen a day later. Three or four birds have usually arrived by 18 April. Then numbers increase rapidly:

1. (i) in 1973, 12 birds were seen on 20 April, 80+ on 8 May;

2. (ii) in 1974, 59 birds were seen on 20 April, 120 on 8 May;

3. (iii) in 1975, 63 birds were seen on 2 May, 200+ on 15 May.

In 1974, when the most careful and detailed counts of arriving Arctic Skuas were made, a total of 116 pairs eventually bred on Fair Isle. About 25 per cent of the breeding birds had arrived by 30 April, 50 per cent by 8 May. The first arrivals are breeding birds that were colour-ringed in previous seasons. Non-breeding birds arrive much later, forming ‘clubs’ in late June. As we have already seen (table 2.5, section 2.3, chapter 2), the Bonxies arrive about two or three weeks before the Arctic Skuas. The Bonxies thus gain a great advantage in the competition for territories: a Bonxie may already have established himself on an Arctic Skua's territory before the Arctic Skua returns. The Arctic Skua is forced to seek an unoccupied territory elsewhere.