The migration of Red Knots through Porsangerfjord in spring 2012: a progress report on the Norwegian Knot Project

We report on the Norwegian Knot project for 2012. The stopover population in Porsangerfjord and Lille Porsangerfjord was estimated at 40,000. The first Red Knots (3,500) had already arrived in Lille Porsangerfjord when fieldwork began on 10 May. Numbers increased daily to 9,000 on 14 May and  40,000 on 15 May when arrivals coincided with a strong SE wind. In the afternoons of 17–20 May, 14  flocks comprising a total of 2,600 Red Knots were seen leaving after the high tide in the direction of Varangerfjord (130 km ESE). Between 23 and 26 May, 13 individually-marked Red Knots that had been recorded a few days earlier in Lille Porsangerfjord/Veidnes were seen there, indicating that Varangerfjord was the destination of the birds seen departing. About 40,000 Red Knots were located in the Lille Porsangerfjord/Veidnes area until 22 May when most left. There were then 18,000 spread along the E and SW shores of Porsangerfjord and between 24 and 29 May, 35 marked individuals which been sighted a few days earlier in the Lille Porsangerfjord/Veidnes area were seen here. Assuming a survival rate of 84%, 29.1% of birds marked in 2006–2009 and expected to be alive, were sighted.  Densities of marked birds were similar at Porsanger and Varangerfjord (mean 1:98). Sampling for Baltic Tellin Macoma balthica, thought to be a major prey of Red Knots staging in Norway was carried out in Balsfjord, Porsangerfjord (Austerbotn and Mårnes) and Lille Porsangerfjord. The highest densities and most suitable sizes for knots were in found at Balsfjord in an area that has been little used by knots for many years. The lowest densities and with most Macoma too large to be swallowed by Red Knots were at Lille Porsangerfjord, a site which has been heavily grazed by knots for three years.  Therefore changes in the availability of this key food resource cannot explain why the distribution of Red Knots has been chabging in N Norway. There has been heavy predation by Peregrine Falcons Falco peregrinus in recent years, so this may be the factor that is driving the change in distribution.