Individual study: Effect of the provision of nest boxes on clutch size and incubation by mandarin duck Aix galericulata breeding near Guildford, Surrey, England
Davies A.K. & Baggott G.K. (1989) Clutch size and nesting sites of the mandarin duck Aix galericulata. Bird Study, 36, 32-36
In Britain, the mandarin duck Aix galericulata (an introduced species from eastern Asia) breeds mainly in natural tree cavities, but they may also use nest boxes. This study compared the clutch sizes of mandarins nesting in tree cavities and nest boxes at a site near Guildford (51º14'N, 0º35'W), Surrey, southern England, between 1972 and 1985.
Natural nest sites were located during 1972-1985 by searches of potentially suitable (i.e. more than 50 cm deep) tree cavities. From 1978, up to 11 wooden nest boxes were also erected on trees overhanging the 0.5 km of stream running through the study area. Boxes were initially erected at a height of 4-8 m, but this was gradually reduced to 1.5 m or less during the study. The floors of boxes were covered with fresh wood shavings in March of each year.
Nests were visited at weekly (or more frequent) intervals between mid-March and early July to monitor the size and incubation of clutches.
Between three and nine natural nest sites were occupied by mandarin each year during 1980-1985, i.e. on average 63% (range: 33-100%) of apparently suitable sites were used each year. Nest boxes were first used in 1980, when one of the six boxes available was occupied. Between five and 10 boxes were then used each year during 1981-1985, or on average 75% (range: 56-100%) of those provided. In total, 42 clutches were laid in nest boxes during 1980-1985.
In nest boxes (12 of 42) and natural sites (7 of 24 clutches during 1972-1985), 29% of clutches laid were not subsequently incubated. During 1980-1985, when both types of nest site were used, incubated clutches in nest boxes (median: 15.0 eggs; n = 28) were significantly smaller than those in natural cavities (median: 22.3; n = 7). However, as there was no significant change in the size of incubated clutches in natural sites (the median of which had been 16.0 before 1980) following the provision of nest boxes, overall, the total number of eggs incubated each year increased substantially.
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