ARTICLES ON HAWAIIAN AND PACIFIC BIRDS, BIRDWATCHING AND WILDLIFE

Three Tundra Swans (Cygnus columbianus) on Maui in October 2003 with brief notes on measurements


Three juvenile Tundra Swans were found in a sugar mill settling pond near Kahului Airport, Maui on October 28th 2003. It was decided by airport staff and local Government agencies that they posed a danger of colliding with aircraft and staff supposedly tried hazing and capturing the birds. One individual was captured and the other two were killed by Wildlife Services (USDA, APHIS). The captured bird was taken to Kawainui Marsh, O'ahu and released on 7th November 2003, but was not seen subsequently. One of the Maui Swan carcasses was sent to the Bishop Museum on O'ahu and examined by Peter Pyle where he confirmed the species identification. The bird was in full juvenile plumage, not yet starting to moult, and possibly a female since measurements were on the low side.

Tundra Swan is a very rare vagrant to the Hawaiian Islands, with just one previous record. Two races occur of the species, the North American sub-species "Whistling Swan"(columbianus) and the Eurasian/Siberian sub-species "Bewick's Swan" (bewickii) which winters in Europe and eastern Asia. Only the American race columbianus has been confirmed as having occurred in Hawai'i, however the measurements of the Maui carcass may indicate that it is of the form bewickii. The American race has also been recorded as a rare vagrant to Europe. In 2003 the Taxonomic Sub-committee (TSC) of the British Ornithologists' Union Records Committee (BOURC) suggested that Whistling Swan C. c. columbianus and Bewick's Swan Cygnus c. bewickii continue to be treated as conspecific (Ibis 146: 153-156).

Hawaiian Islands Tundra Swan records:

19?? - One of the North American form columbianus was present on Midway.

2003 - Three juveniles of as yet undetermined race were found in a sugar mill settling pond near Kahului Airport, Maui on October 28th. One individual was captured and the other two were killed by Wildlife Services (USDA, APHIS). The captured bird was taken to Kawainui Marsh, O'ahu and released on 7th November, but was not seen subsequently.


Peter Pyle who took the measurements of the Maui Swan carcass had recently been summarizing measurements from the literature for all waterbird species and below are the summaries for Trumpeter and Tundra swans for comparisons. All measurements fit Tundra Swan and all measurements are far too small for Trumpeter Swan. The tail measurement is too small for the North American subspecies columbianus (Whistling Swan) but Peter cautions that this might have resulted from measurement technique or an error on his part. If it is a Whistling Swan the other measurements indicate that it was likely a female. However, all measurements (including tail) fit the Eurasian subspecies bewickii (Bewick's Swan) as well. If it turns out to be a male (by gonads) Peter states he would lean towards it being a Bewick's Swan based on measurements alone. Peter says that otherwise, he was unable to make a subspecific determination based on physical features and it may be difficult with juveniles.


Table 1. The standard measurements of the 2003 Maui specimen.

Exposed culmen from tip of down feathers

Exposed culmen from tip of contour feathers

Wing chord

Flattened wing length

Tail

Tarsus

Maximum tarsus

             

86 mm

89 mm (this should be used for comparison)

490

519 mm

135 mm

104 mm

116


Table 2. Measurements (mm) in North American swans to assist in identification, ageing, and sexing. Values were derived from 95% confidence intervals as based (for wing, exposed culmen, and tarsus) approximately on the indicated sample sizes; sample sizes for tail length and bill depth were often smaller but included at least 10 of each sex (table provided by Peter Pyle).

Taxon/Sex

 

n

Wing Chord AHY/ASY(HY/SY)1

Tail Length

Exposed Culmen2

Bill Depth3

Tarsus

               

Tundra Swan

             
C.c. bewickii              
Female  

100

468-544 (444-521)

126-160

78-101

33.8-42.8

86-113

Male  

100

489-561 (469-538)

132-166

82-105

36.0-45.1

90-117

               
C.c. columbianus              
Female  

100

483-556 (467-539)

149-183

87-116

39.6-49.6

96-119

Male  

100

511-574 (493-556)

155-190

92-120

41.9-51.7

101-124

               

Trumpeter Swan

             
Female  

30

559-649 (534-623)

164-221

96-123

40.7-50.2

106-133

Male  

30

599-690 (574-663)

176-234

102-129

44.8-53.4

112-138

               
1 Wing chord differs substantially by age; other measurments less age-specific and given values refer to all age groups (except see 2).
2. Exposed culmen values are from ASY/ATYs only. HY/SYs and SY/TYs have smaller and more variable values due to variably receding distal extensions of downy forehead feathering, rather than bill size.
3. Bill depth measured at the distal end of knob (adult Mute Swans) or forehead feathering of adults, not including downy extension of Juvs.


Three juvenile Tundra Swans by settling pond near Kahalui Airport, Maui, October 2003.

The second record for the Hawaiian Archipelago.

Photograph © USDA/APHIS

Juvenile Tundra Swan in captivity, Maui, October 2003. Two other juveniles were slaughtered by USDA/APHIS. This juvenile was captured and released on O'ahu.

Photograph © USDA/APHIS

Thanks to Peter Pyle for providing details of the measurements of the Maui bird, as well as details of measurements of other individuals. Thanks also to those who have contributed to the debate on the identification and details of the occurrence of the Maui birds, which include Peter Donaldson, Lance Tanino, Doug Pratt, Fern Duvall, Eric VanderWerf, Jaan Lepson and members of the Hawaii Birding Chatlist Group.



References

COLLAR, N.J., M.J. CROSBY and A.J. STATTERSFIELD. 1994. Birds to Watch 2. The World list of Threatened Birds. Birdlife International. Cambridge , U.K.

DELACOUR, J. 1954. The Waterfowl of the World. London.

DEL HOYO, J.; ELLIOTT, A.; and SARGATAL, J. 1992 - 2002. The Handbook of the Birds of the World, Volumes 1. Ostrich to Ducks. Lynx Edicions, Barcelona.

GODFREY, W.E. 1986. The birds of Canada. Revised edition. National Museums of Canada. Ottawa.

JOHNSGARD, P.A. 1981. Waterfowl of North America. Indiana University Press. Bloomington.

MADGE, S. and BURNS, H. 1988. Wildfowl. London.

OGILVIE, M. and YOUNG, S. 1998. Wildfowl of the World. New Holland, London, UK.

PATTEN, M.A. and HEINDEL, M.T. 1994. Identifying Trumpeter and Tundra Swans in the Field. Birding.

PRATT, H.D. , BRUNER, P.L. and BERRETT, D.G. et al. 1987. A Fieldguide to the Birds of Hawai'i and the Tropical Pacific. Princeton.

PYLE, R. L. 1992. Checklist of the Birds of Hawaii - 1992. The 'Elepaio 52: 53-62.

SCOTT, P. 1972. The swans. Michael Joseph. London, U.K.

WILMORE, S.B. 1974. Swans of the world. David and Charles. Newton Abbot, U.K.

Christian Melgar, West Sussex, UK. 2003.

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