THE SIZE AND SHAPE OF EGGS FROM A WELSH POPULATION OF PIED FLYCATCHERS - TESTING HOYT USE OF EGG DIMENSIONS TO ASCERTAIN EGG VOLUME

A miniaturized version of the volumeter described by Szekely et al. (1 994) was used to measure the volume of several hundred eggs from Welsh populations of the Pied Flycatcher (Ficedula hypoleuca) and to compar e volumes so measured with those calculated from the eggs' dimensions using Hoyi's equation. As Szekely et al. (1994) discovered on a small sample of plover eggs, Hoyt's formula consistently overestimates egg v olume, in the case of Pied Flycatcher eggs by about 2%. The eggs of fl ycatchers that nest in central Wales are similar in size and shape to those reported for European and English populations of this species. E gg length (L), breadth (B), and volume (V) averaged 17.74 mm, 13.32 mm , and 1.58 cm(3), respectively. The egg's elongation or shape index (L /B) was most often between 1.30 and 1.35. Volume can be measured direc tly (and easily) using a volumeter, but it can also be estimated, if n ecessary, at least in so far as Welsh birds are concerned, from the di mensions of the egg using the formula V = 0.1178 + 0.4637LB(2) or from the egg's volume coefficient of 0.500, in which case V = 0.500LB(2).