Timing of breeding in Ruff Philomachus pugnax: a crucial parameter for management and use of wet grassland in Western Europe

Numbers of Ruff Philomachus pugnax breeding in temperate wet grassland have declined markedly all over Europe during the last 30–50 years. However, at Tipperne, a breeding site in W Denmark with favourable meadow bird management, Ruffs still breed in numbers similar to 50 years ago. The number of breeding Ruffs at Tipperne has been monitored annually since 1928, and since 1999 also breeding performance was assessed, by mapping alarming females during the entire breeding season. In this paper, data on the timing of hatching and presence of broods are presented, information that is relatively scarce for Ruffs breeding in temperate areas.

At Tipperne, Ruffs have a very long nesting season, from early May until late July; the mean hatching date in 1999–2015 was 14 June and the 10th and 90th percentiles were 3 June and 4 July. Chicks stay hidden in the meadows until they fledge at an age of three weeks, and an estimated 80% of hatched chicks fledge by 16 July, and 90% by 25 July. The timing of breeding had not changed during the 20th century, but in 1999–2015 onset of breeding was ca. one week later compared to earlier decades, possibly because in the late 1990s Barnacle Geese Branta leucopsis started grazing intensively on the meadows in April–May, and the grass sward is now strikingly shorter in May than before the geese appeared.

The wetness of the grassland at Tipperne is primarily dependent on precipitation, and breeding seasons were more than two weeks longer in wet years (until late July) compared to normal and dry years (until early to mid-July). The long and late breeding season of Ruffs means that the timing of management practices should be adjusted accordingly, with postponed grazing schedules, moderate grazing densities in the nesting season, and mowing postponed until the second half of July. These practices, taking the very late breeding of the Ruff into account, could significantly improve chances for Ruffs to breed successfully in wet grassland conservation areas.