Mute Swans (Cygnus olor) are the largest breeding bird in Britain, with a wingspan of more than two metres and weighing up to 14kg. The White-tailed Sea Eagle (Haliaeetus albicilla) may have a slightly bigger wingspan but carries nothing like the weight. Mute Swans can eat around 4kg of vegetation a day, and are capable of having an impact on flora, notably Water Crowfoot (Ranunculus spp).
Their numbers have increased since a ban on the use of lead shot for angling was introduced in 1987, with more than 20,000 now resident in the UK. They are not migratory here, and few if any of those which depart northern Europe each year spend the winter in the UK.
Unfortunately, while the ban on lead shot was humane and essential, the fact that the Mute Swan has no natural predators, and can breed for five or six years on average with up to eight young each time, means there is a resulting conundrum, even allowing for 50 per cent mortality among cygnets in the first three months.
The issue is this – if a species is protected and numbers increase with no equivalent boost to possible nesting sites, is the protection anything more than a poorly-thought-out half-measure? Not that increasing the number of potential breeding areas arbitrarily was ever a practicable proposition. Mute Swans are highly territorial and do not nest colonially except at the Swannery at Abbotsbury in Dorset. Their territories can extend for 3km and any intruders are likely to be given a dusty response. The inevitable outcome of this is that non-breeding herds at such locations as Windsor and Reading have grown significantly in size and are unlikely to reduce.
Aggression – perhaps fierce protection would be a better description – is greatest during the five weeks while the pen (female) is on the nest or after the cygnets have hatched.
Travelling on the pen’s back in the first couple of weeks is common, especially if there are pike on the premises or the watercourse is flowing faster than expected because of rain. Some birds even occupy two sites, one for breeding safely and another for bringing up the youngsters – the cob (male) pictured above leading cygnets across an arable field was one of a double act which nested on a pond then walked 100 metres to get to a river, where the feeding was better.
There is only one colour variation with Mute Swans, the so-called Polish Swan, sometimes falsely given the scientific name Cygnus immutabilis as though it were a different species. As a result of a sex-linked recessive inheritance, the down of Polish cygnets is white rather than grey, and the legs of young and adults are paler than usual. Polish Swans are rare in Britain, slightly commoner in the Netherlands and most numerous in eastern Europe, where the tally can be as high as 20 per cent in places, However, the description Polish has no special justification.
Images © Jeremy Early. All rights reserved.