Een dwerglegsel bij de Torenvalk Falco tinnunculus

In 2006 we encountered a clutch of the Eurasian Kestrel Falco tinnunculus containing 5 very small eggs (Table 1 & Photo 1) in a nestbox in the Lauwersmeer area, a nature reserve located in the northern Netherlands. All eggs were smaller than 40% of the average egg size of the Kestrel as reported in the literature, and 50% smaller than the smallest egg ever reported (Table 1). All eggs were typical Kestrel eggs except for size (Photo 1). None of the eggs contained egg yolk, but all eggs held some blood or embryonic tissue residue, the amount of which varied from a tiny speck to the size of a drop (Photo 2). Without this residue, egg formation would probably not have occurred. Runt eggs are not commonly found (overview in Table 2). In raptors few runt eggs have been recorded, for example in the Goshawk Accipiter gentilis 0.3% of 1011 eggs. Reports of runt clutches are very scarce. To our knowledge this is the first report of a runt clutch in a raptor species.