Function of the uropygial gland in eiders (Somateria mollissima)

Anders Pape Møller,Karsten Laursen

doi:10.1186/s40657-019-0163-8

Abstract

BackgroundThe uropygial gland is an exocrine gland located above the tail of birds that produces a diverse range of biochemicals. It has been hypothesized to be involved in chemical protection, water-proofing and maintenance of plumage brightness. Although these not necessarily mutually exclusive functions have received some empirical support, there has been little empirical research on the function of water-proofing.MethodsHere we analyzed data for 229 individual eiders (Somateria mollissima) collected by Danish hunters during 2016‒2018.ResultsThe Eider is a sea-duck that spends almost its entire life in sea water emphasizing water-proofing of the plumage. The size of the uropygial gland increased with body mass in males, but not in females, and it increased with age. The size of the uropygial gland decreased during winter. Eiders with small uropygial glands grew their feathers at a fast rate. Eiders with large wing areas had large uropygial glands.ConclusionsThese findings are consistent with large uropygial glands playing a role in water-proofing during molt and foraging, but also that uropygial glands may play a role in chemical defense.

Highlights

The uropygial gland is an exocrine gland located above the tail of birds that produces a diverse range of biochemicals
The function of the secretions by the uropygial gland has been hypothesized to vary from anti-microbial substances, waterproofing, drag reduction, and excretion of pollutants to intraspecific and interspecific communication
The mass of the uropygial gland increased with body mass in males, but not in females in which uropygial mass was basically constant across the range of body masses [sex: χ2 = 89.87, df = 1, p < 0.0001, estimate (SE) = 0.612 (0.06); body mass; χ2 = 6.67, df = 1, p = 0.01, estimate (SE) = 0.91 (0.35); sex × body mass: χ2 = 12.75, df = 1, p = 0.0004, estimate (SE) = 1.27 (0.35)]

Summary

Introduction

The uropygial gland is an exocrine gland located above the tail of birds that produces a diverse range of biochemicals. The function of the secretions by the uropygial gland has been hypothesized to vary from anti-microbial substances, waterproofing, drag reduction, and excretion of pollutants to intraspecific and interspecific communication (review in Elder 1954; Jacob and Ziswiler 1982; Salibián and Montalti 2009; Moreno-Rueda 2017). There is Another reason for the lack of consistency in research findings is the absence of studies investigating the fitness consequences of production of different amounts of secretions (Elder 1954; Salibián and Montalti 2009; Giraudeau et al 2010a; Møller et al 2010). Møller unpublished data on 2065 adult Barn Swallows Hirundo rustica)

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