Dwergeieren bij Bonte Vliegenvanger Ficedula hypoleuca

Bijlsma R.G. 2013. Incidence of runt eggs in Pied Flycatcher Ficedula hypoleuca. Drentse Vogels 27: . During a study in the northern Netherlands in 2077-2013, a total of 5839 eggs of Pied Flycatchers were measured, of which 16 were defined as runt eggs (i.e. eggs that were 75% or less in volume than the average egg), i.e. 0.27%. Of 16 runt eggs, only four hatched (invariably the largest of the runts, Table 1), the remaining failed to hatch (or were depredated before hatching could have occurred). Runt eggs were found in six different nests, two of which involved complete clutches (5 and 6 eggs) of the same female (individually identified by ring number; male presumably different in second year, based on plumage characteristics), two runts were found in a C/6 (both hatched), one runt was found in a C/6 (depredated) and in a C/7 (hatched), and one very small runt was found in a clutch not yet completed (and depredated; this egg measured 10.0x8.3 mm (0.351 cm, compared to average volume of 5823 eggs of 1.627 ). Hatching still seemed possible for eggs only 69% of the volume of the average egg in the local population; when smaller, hatching is unlikely. Mean egg volume showed small variations between years (Table 2), with a hint of increase when May temperatures were high (Fig. 1), but overall variation was large (range for 5823 eggs, excluding runts, was 1.239-2.082 cm).