ALBERT

Description: Once thought to be extinct, the Tasman Booby Sula tasmani has recently been re-classified as a subspecies of the Masked Booby S. dactylatra on the basis of genetic data. This re-classification raises the issue of whether this novel clade has a distinct morphology. Morphological differences in size, as well as coloration of integuments, bill and iris have been found in other subspecies of the Masked Booby but have not yet been reported for live Kermadec Islands breeding individuals. Museum specimens from this breeding location have been separated from other Pacific breeding subspecies by their longer wings. We sampled a total of 21 individuals from North Meyer Islet, Kermadec Group, New Zealand, and applied molecular sexing to obtain sex-specific morphometric measurements. We matched dimorphism in vocalization with genetic sexing results and photographic documentation of human-assessed bill, foot and eye coloration. While culmen measurements were consistent with reports from museum specimens, wing chords from living specimens of Tasman Masked Boobies were 3% and 4% larger in males and females, respectively. Females had larger culmens and wings than males, consistent with the low extent of sexual dimorphism reported from museum skins. Adult Tasman Masked Boobies had yellow to buff-yellow feet, while fledglings, as in most sulids, had grey to greyish-yellow feet. Our findings confirm the distinctively long wing and particular iris coloration previously reported for the taxon and provide the first description of integument coloration of live specimens. This study highlights the importance of including in situ assessment in taxon descriptions.

Description: Data on the extent to which the sexes may differ in their phenotypes are critical for a full understanding of the biology and management of any species. We previously quantified behavioral differences and vocal similarities between genetically-sexed Australasian Gannets (Morus serrator). Here, we quantify size monomorphism and plumage dichromatism in this socially monogamous, colonial seabird. In comparison with other sulids, the Australasian Gannet is characterized by low sexual dimorphism indices in various size metrics, and most physical dimensions are statistically similar between adult female and male gannets. In contrast, we found indications of sexually dichromatic plumage traits in the melanin-based, rusty head plumage and in the black-and-white tail feathers. To our knowledge, these findings constitute the first evidence of melanin-generated sexual plumage dichromatism in a size monomorphic seabird species. Using opsin-sequencing, we also confirm that the Australasian Gannet is a visually violet-sensitive species, for which the detection of both gross differences in feather reflectance, and long-wavelength based plumage dichromatism, should be perceptually feasible. However, because of the extensive overlap between females and males in the size and chromatic traits detected here, and in the behavioral and vocal displays reported in previous studies, we advocate for the use of genetic techniques for sex identification in this gannet species.