Prefledging survival of Mute Swan Cygnus olor cygnets in the Lothians,UK

Capsule Survival rates 1981–98 were quantified between four growth stages, and related to habitat type and altitude

Aims To investigate variability in Mute Swan productivity in relation to habitat type and altitude.

Methods Cygnets were studied and categorized as they developed from small size through medium and large to fledged. Natal territory was classed as river, canal or still water, and altitude of each site established.

Results Of 2576 cygnets studied, 69% fledged. Fledging rate varied from 57% on low altitude still waters to 78% on mid-altitude still waters, and from 72% on rivers to 82% on canals. Survival was lower between the early growth stages. Of the pairs that bred, 72% produced at least one small cygnet and 61% fledged at least one cygnet. Pairs that nested on rivers suffered the greatest loss of complete clutches or broods of newly hatched cygnets and 41% failed to raise at least one small cygnet. The breeding population increased annually by 7% from 15 pairs to 69 pairs between 1978 and 1998 and consequently the number of cygnets fledged increased annually by 7%. Productivity was higher than in other populations at 2.6 cygnets fledged per breeding pair; ranging from 2.1 on rivers to 3.6 on mid-altitude still waters.

Conclusions Cygnet survival was lower during the early growth stages across all habitats. Survival was consistently poorer on low altitude still waters, probably due to inadequate diet. Although survival in the Lothians varied with habitat type and altitude, productivity was higher than in other areas of Britain.