The growth and development of W hooper Swan cygnets Cygnus Cygnus

J Bowler
The growth and d evelopm en t o f ten captive W h ooper Swan cygnets hatched at the Wildfowl & Wetlands Trust Centre at L la n e lli on 10-13 M ay 1990, were docum ented fo r the first 23 weeks o f life. Weekly recording o f biom etrics, together with a ph otogra ph ic record, revealed: rapid growth with the first con tou r feathers appearing at 4.3 weeks and a 30-fold increase in w eight re la tiv e to ha tch in g w eight within n in e weeks. F ledging o ccu rred at arou n d 11.4 weeks, when
more » ... e birds had ach ieved 79% o f m ean adult mass; and the tarsus reached 99.8% o f its m ean adult length by 18 weeks. M ales were always h e a v ie r and usually la rger on average than females o f the same age. Data obtained were com pared with oth er published studies. D e v e lo p m e n t was m o re ra p id than that f o r w ild W h o o p e r cygnets in Ice la n d indicating that captive rearing conditions were overcom in g the presum ed detrim ental effect o f shortened day length, with low er latitude, upon tim e available fo r feeding. T h e W h o o p e r Swan Cygnus Cygnus breeds m ainly in the taiga and scrub zo n e of N orthern Eurasia b etw een latitudes 45° and 70°N in a range stretch ing from Ice­ land in the w est to the Pacific coast o f the USSR in the east, and m igrates south each autumn to w in ter at lo w er latitudes (O g ilv ie 1972). T h e tim e available fo r nest­ ing and the rearing o f juveniles b e fo re the fam ilies d epart on autumn m igration is short and consequently, in com m on with oth er northern swans, cygnets exhibit sub­ stantial w eight gains and steep grow th curves com p ared w ith oth er sp ecies (K ear 1972). T h e effect of latitude upon grow th rates has been dem onstrated in the closely related T ru m peter Swan Cygnus buccina­ tor, cygnets o f w hich achieved first flight at 17.1 weeks on Jackson Lake, W yom in g at 44°N (Sim on 1952) but reached the same stage after on ly 12 weeks at Kenai, Alaska at 60°N (T r o y e r in prep .). This v ie w was also shared by Owen & Black (1990) w h o noted that the T ru m peter Swans in Alaska fledged in a sh orter p eriod than the sim i­ larly sized M ute Swans Cygnus o lo r in Eng­ land, w hich th ey attributed both to differ­ ences in the quality and availability of food in the tw o regions and to the breed in g lati­ tude. G rowth rates of cap tive swans have been rep o rted to be slow er than th ose in the wild, for exam ple B ew ick's Swans Cygnus columbianus bew ickii took m ore than tw ice as lon g to fledge at Slim bridge (5 2 °N) than in the A rctic tundra at 70°N (K ear 1972). Such differences have been attributed p artly to d ietary factors but m ore im por­ tantly to the effect of sh orten ed daylength at lo w er latitudes reducing tim e available for feeding. T h e B ew ick's Swan cygnets bred in cap tivity w ere reared b y th eir par­ ents, h ow ever, and the effect o f hand-rear­ ing cygnets on a high-protein diet in con ­ fined and rela tively disturbance-free pens was unclear. T h e aim of the study was to docum ent the d evelop m en t and grow th of hand-reared W h oo p er Swan cygnets, first to p ro v id e a com parison w ith available published data con cernin g swan grow th rates and seco n d ly to p ro v id e a scale of d evelop m en t fo r classifying cygnets of unknown history on the b reed in g grounds.