MEININGER PL, SWELM ND VAN & SWENNEN C (1987) Biometrics, moult, and origin of Little Terns Sterna alhifrans in SW. Netherlands. LIMOSA 60 (2): 75-83.

Biometric and moult data of Little Terns Sterna alhifrans captured on the nest (n = 129) and after the breeding season (n = 92) in Sw. Netherlands in 1982 - 1986 are presented (tab. 1-4, fig. 1-3). The mean weight of adults on the nest (x = 55.7 g) was significantly higher (t = 3.13, P < O.O!) than that of adult non-breeders in mid July (x = 53.6 g). Between mid July and 10 September weights of adults and first year birds showed average daily increases of 0.08 and 0.18 g respectively (n.s., tab. 3). A positive correlation was found in adult breeding birds between weight and bill, wing and tarsus length (tab. 4). The three linear body measurements were positively correlated to each other (tab. 4). The Little Tern has a complicated primary moult pattern. In summer three generations of primaries are generally present. It was found to be difficult to distinguish between these various generations. The earliest indication of adults in primary moult was on 30 June, when two moulting breeding birds were captured on nests. Three out of ten adults captured on 17 July had not yet commenced primary moult. Out of 45 adults examined between 17 August and 10 September 42 were replacing primaries, their moult scores varied from 6 to 36 (fig. 1). The number of growing primaries decreased with increasing total primary moult score (fig. 2, 3). The remaining three birds were not actively replacing primaries (moult scores 25, 30 and 35) and had probably suspended their primary moult. The trapping of adults on the nest seemed to have little negative effect on breeding success, providing it is done with care. Of the 34 nests adults were trapped, 24 (71 %) were successful (hatched young), 3 (9%) were abandoned, and of 7 (20%) the outcome was unknown; compared to an undisturbed sample of 36 nests in the same colony in which the outcomes were 29 (81 %), 4 (11 %), and 3(8%), respectively. In the North Sea area, natal and breeding dispersal appear to be relatively large (fig. 4, app. I). Between mid August and 10 September the local breeding population of SW. Netherlands is augmented by migrants from Finland, the German- Danish Baltic area and the German-Danish Wadden Sea.

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