Egg volume can be accurately and efficiently estimated from linear dimensions for Arctic-breeding shorebirds

Avian egg size reflects an important component of a female’s energy investment in reproduction, yet equations for estimating egg volume from easily measured linear dimensions have not been well developed and assessed for many shorebird species. We derived species-specific egg volume coefficients (Kv) for use in Hoyt’s (1979) volume estimation equation V = Kv * LB2 by measuring length (L), breadth (B), and volume (V) of eggs belonging to a suite of arctic-breeding shorebirds near Barrow, Alaska. The overall mean Kv for the five species studied was 0.471, with species-specific values ranging from 0.468 to 0.474. Kv values did not differ significantly among species and were similar to the few published values for other Scolopacidae, suggesting that a Kv of 0.471 may be generally applicable to this family. We also estimated egg volumes (V) from empirically derived species-specific regression equations in the form of V = a * LB2 + c. Volume estimates made with the species-specific Kv, the mean Scolopacidae Kv, and species-specific regression equations were accurate and precise, with absolute error equivalent to only 0.9–1.4% of mean egg volume within each species. These estimation techniques offer a substantial improvement for estimating volume over Hoyt’s (1979) general avian Kv of 0.51 (which had error equivalent to 7.7–9.0% of egg volume). We summarize Kv values for shorebirds from the literature and recommend these indirect approaches, which rely on simple measures of egg length and breadth put into derived equations, for estimating egg volume in shorebirds. This recommendation is particularly applicable in field investigations where direct measures of egg volume are difficult to conduct.