Measurements of the 23 June 2021 Wedge-tailed Shearwater in Bishan

Pelagic birds are rather scarce in Singapore, so news of the grounded Shearwater found at Bishan-Ang Mo Kio Park on 23 June must have caught everybody by surprise. The bird was originally found by a passer-by below a HDB block in the area and then transported to the park. It was later spotted by William Khaw, who alerted the birdwatching community and ACRES. Many others contacted ACRES as well but despite being rescued, the bird did not survive. I was fortunate enough to take a look at the bird’s carcass with my colleagues and managed to get some measurements that are reproduced below. While photographs of the bird are aplenty online, I hope that these numbers will help serve as primary documentation for future birders as well as help those still wavering on the identification.

FeatureMeasurements of the Bishan bird (mm)Measurements (mm) of Wedge-tailed Shearwaters (WT) and Short-tailed Shearwaters (ST)
Tail119.0WT: 123-138
ST: 78-85
(Pettit et al., 1984; Longmore, 1985; Wells, 1999).
Bill depth at base11.3 –
Bill depth at nare (tip of the nostril)10.2 –
Minimum bill depth7.4 –
Bill to skull46.5 –
Bill to feathers39.0WT: 38.47±1.89
ST: 31.82±1.37
(Bull et al., 2005)
Head plus bill81.8 –
Wing279.0WT: 292.99±9.99
ST: 267.11±13.06
(Bull et al., 2005)
Tarsus47.3 –
Mid-toe (including claw)58.5 –
Mid-toe (without claw)50.7 –

The Wedge-tailed Shearwater Ardenna pacifica can be distinguished from the more locally expected (though still rare) Short-tailed Shearwater A. tenuirostris from a number of features. These include the bill shape (comparatively long bill to head ratio) and the tail extension (long in Wedge-tailed Shearwater, shorter in Short-tailed Shearwater). For those who are less familiar, comparison of the measurements against other sources unequivocally confirm the identification as a Wedge-tailed Shearwater; the similar looking Short-tailed Shearwater measures much smaller.

Of the three species of Shearwaters that have been recorded regionally so far, the Short-tailed Shearwater is the most expected around the nation. Although a rare bird locally, it has been reported semi-regularly in recent years along the Singapore Straits during pelagic trips (https://ebird.org/species/shtshe). Instead, there is only one record of the Wedge-tailed Shearwater so far, yet another grounded bird that was photographed at Woodlands on 22 June 1998 (Wang & Hails, 2007). Coincidentally just 1 day apart, although 23 years ago! The third species, Streaked Shearwater Calonectris leucomelas is expected, though no verifiable records are present as of yet.

If you find any wild animal that needs help, please contact ACRES at 97837782 and/or the NParks hotline at 18004761600.

Acknowledgements

Massive thanks to the staffs at ACRES, especially Kalai and Ava, who helped keep and pass the carcass to the NUS Avian Evolution Lab, to all who assisted in the rescue process, and to William Khaw for sharing the sighting with the community. I would also like to express my gratitude to Art Toh, Dillen Ng, Martin Kennewell, Movin Nyanasengeran and Tan Hui Zhen for the help in preparing this short piece.

Literature cited

Bull, L. S., Bell, B. D., & Pledger, S. (2005). Patterns of size variation in the shearwater genus Puffinus. Marine Ornithology, 33, 27-39. Link: http://www.marineornithology.org/PDF/33_1/33_1_27-39.pdf

Longmore, N. W. (1985). Two new records of the short-tailed shearwater from north Queensland. Sunbird: The Journal of the Queensland Ornithological Society, 15(4), 84. Link: https://birdsqueensland.org.au/sunbird_issues/Sunbird_Vol15_No4.pdf

Pettit, T. N., Byrd, G. V., Whittow, G. C., & Seki, M. P. (1984). Growth of the Wedge-tailed Shearwater in the Hawaiian Islands. The Auk, 101(1), 103-109. Link: https://sora.unm.edu/sites/default/files/journals/auk/v101n01/p0103-p0109.pdf

Wang, L. K., & Hails, C. J. (2007). An annotated checklist of the birds of Singapore. Raffles Bulletin of Zoology, 15, 1-179. Link: https://lkcnhm.nus.edu.sg/wp-content/uploads/sites/10/app/uploads/2017/04/s15rbz001-179.pdf

Wells, D. R. (1999). The birds of the Thai-Malay peninsula (Vol. 1). London: Academic Press.

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