. The Canadian field-naturalist. 278 The Canadian Field-Naturalist Vol. 93 Table 3âMean ±sd (N) weights and measurements of Black Tern eggs Egg Egg 2 Egg 3 All eggs Weight (g) Length (mm) Width (mm) Shape index^ ± (8) ± (19) ± (19) ± (15) ± (6) ± (13) ± (13) ± (12) ± (6) ± (20) ± (20) ± (18) ± (20) ± (91) ± (91) ± (74) '100 X width/length (Colhns and LeCroy 1972). (Table 3), although third eggs were longer and narro
. The Canadian field-naturalist. 278 The Canadian Field-Naturalist Vol. 93 Table 3âMean ±sd (N) weights and measurements of Black Tern eggs Egg Egg 2 Egg 3 All eggs Weight (g) Length (mm) Width (mm) Shape index^ ± (8) ± (19) ± (19) ± (15) ± (6) ± (13) ± (13) ± (12) ± (6) ± (20) ± (20) ± (18) ± (20) ± (91) ± (91) ± (74) '100 X width/length (Colhns and LeCroy 1972). (Table 3), although third eggs were longer and narrower and had a lower shape index (Collins and LeCroy 1972). There was a tendency for the first egg to be smallest and the second to be largest (Table 4). In contrast, the smallest egg for Common Terns {Sterna hirundo) is usually the third one. As in Black Terns, the third egg is usually the most narrow (Gemperle and Preston 1955; Gochfeld 1977). Fresh egg weight of Black Terns was of adult body weight, a slightly lower percentage than shown by the larger Common and Roseate Terns {S. dougallii) (Collins and LeCroy 1972). Weights of three freshly hatched chicks averaged g, and subsequent growth is detailed in Figures 1-3. The average weight for day 0 (day of hatch) chicks in Figure 1 includes birds which may have been hatched as much as 10-20 h before being weighed. Weight gain in the chicks shows a pattern very similar to that of other temperate-nesting species. The growth curves of terns can best be fitted to logistic equations, and growth constants calculated for various species are compared in Table 6. Although Black Terns appear to grow more rapidly than the other terns, they Table 4âPercentage of Black Tern nests in which given eggs in the laying sequence were largest, of middle size, or smallest in the clutch. N = 10 clutches. Volume calculated as per Shott and Preston (1975) Egg I Egg 2 Egg 3 Largest in clutch Medium sized Sma
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