Dump Nesting and Its Effect on Production in Wood Ducks

Clutch size and nesting sites of the Mandarin DuckAix galericulata

“…In the present study, eggs in nests of this type constituted about one quarter of all those laid over the period of study, and were not associated with any particular type of site. The median clutch size was larger than the maximum number quoted for Aix sponsa, 10 and the maximum recorded for a single site was 34. Semel & Sherman also found for Aix sponsa a substantial proportion (43%) of nests with eggs abandoned before incubation, but it is not clear whether these eggs shared the same characteristics as eggs from the 'drop nests' of Morse & Wight, or the same features as clutches of unincubated Mandarin Duck eggs.…”

“…Similarly, in Aix sponsa additional nestboxes produced an increase in the numbers of eggs laid within a defined area. 10 In our study area there was little change in the total number of eggs incubated in natural sites by Mandarin Ducks; on average 25.4 eggs/year before 1980, the year in which the first nests in boxes were recorded, and 25.8 egg/year after 1980. In contrast, the average yearly number of eggs incubated in both types of nest site increased almost 4-fold after 1980 to 96.8 eggs/year.…”

“…For some populations of Aix sponsa 'dump nesting', and therefore the size of clutches, was not related to the availability of nest sites. 10 However, in other studies of Aix sponsa a scarcity of nest sites in a rapidly expanding population sometimes resulted in 'dump nestin g'. 12,13 Nests of the Mandarin Duck in tree cavities also contained large clutches, and the introduction of nest boxes to the study area did not significantly alter the clutch size in natural sites.…”

Egg-laying, incubation and intraspecific nest parasitism by the Mandarin DuckAix galericulata

“…25' 6 '°C lawson, Hartmann & Fredrickson 2 found 37% of eggs of the Carolina Wood Duck were laid parasiticially; for the Mandarin Duck approximately a quarter of all eggs were additional eggs laid on days of multiple laying. The proportion of non-term eggs reported for the Carolina Wood Duck was 22% 2 and 13% 5 . This compares with 11% of eggs laid after the onset of incubation by the Mandarin Duck, and confirms the conclusion of Davies & Baggott l that eggs laid parasitically by the Mandarin Duck are mostly added to a clutch prior to the start of incubation.…”

“…Parasitized clutches were identified according to the following features: (a) more than 1 egg laid in the nest on any day; (b) non-term eggs in the clutch; (c) large clutch size. Criteria (a) and (b) involve fewer assumptions than (c); indeed Morse & Wight 5 have shown that using only these two criteria, as well as a break in lay of 3 days or more, some nests with as few as 6 eggs were indeed parasitized. For the Mandarin Duck 56% of clutches visited daily would be classified as parasitized by criterion (a) alone.…”