Visual observation to identify sexes in subspecies of adult Black Skimmers (Rynchops niger)

Vieira, B. P., Furness, R. W. and Nager, R. G. (2018) Visual observation to identify sexes in subspecies of adult Black Skimmers (Rynchops niger). Waterbirds, 41(2), pp. 166-170. (doi: 10.1675/063.041.0207)

Abstract

Identifying sexes in birds from visual observations could be a useful and inexpensive method. While sexual dichromatism and ornaments are readily used by observers, sexual size dimorphism can also be used to identify sexes in some bird species. This study assessed the applicability of visual observation of size differences to identify sexes in adult Black Skimmers (Rynchops niger). Black Skimmers do not have sexual dichromatism; however, Black Skimmer males are skeletally larger (6.7–31.7% depending on trait) and 33.3–37.5% heavier than females. The study focused on two subspecies: Amazonian (R. n. cinerascens) and South American (R. n. intercedens) Black Skimmers. Sex identified by visually observing size differences was consistent with the sex identified at specimen preparation from examining gonads (RGLMM = 0.996 ± 0.004). The identification of sexes from photographs using visual observation of size had a very high within- (RGLMM = 0.995 ± 0.001) and between- (RGLMM = 0.984 ± 0.002) observer repeatability. Non-invasive methods for identifying sex by visual observation may allow enhanced use of data from photographic datasets, citizen science projects, and surveys using direct observation or images.

• Item Type: Articles
• Additional Information: This work was supported by the Brazilian Agency CAPES (BEX 11868-3/9).
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Furness, Professor Robert and Nager, Dr Ruedi
• Authors: Vieira, B. P., Furness, R. W., and Nager, R. G.
• College/School: College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
• Journal Name: Waterbirds
• Publisher: Waterbird Society
• ISSN: 1524-4695
• ISSN (Online): 1938-5390
• Copyright Holders: Copyright © 2018 Waterbird Society
• First Published: First published in Waterbirds 41(2): 166-170
• Publisher Policy: Reproduced with the permission of the Editor