. The Canadian field-naturalist. Natural history. 428 The Canadian Field-Naturalist Vol. 109 1991-2 - T 10 (• T ^ 1 ''4 10 J 1 1 1—" H 1993-4 \2 2 !-f-> J- \2 2 4 ,• t" MAMJJASONDJ F -1 1 1 1 \ 1—•—•—f—1 1 r MAMJ J ASONDJ F 3 - 8- 1992-3 7- 6- 4 3 5 - 4 - 3- 2 - 2 1 3 2 2 1 - 0 - \ l/ 1 V 1—1— M A M J J S O N D J. Figure 3. Mean (± 1 ) numbers of active nests of feral Rock Doves at the study colony, 1991-1994. Sample size given for each month is the number of days on which a nest census was conducted. dates [using an incubation period of days (Johnston 1992) and a fledgin
. The Canadian field-naturalist. Natural history. 428 The Canadian Field-Naturalist Vol. 109 1991-2 - T 10 (• T ^ 1 ''4 10 J 1 1 1—" H 1993-4 \2 2 !-f-> J- \2 2 4 ,• t" MAMJJASONDJ F -1 1 1 1 \ 1—•—•—f—1 1 r MAMJ J ASONDJ F 3 - 8- 1992-3 7- 6- 4 3 5 - 4 - 3- 2 - 2 1 3 2 2 1 - 0 - \ l/ 1 V 1—1— M A M J J S O N D J. Figure 3. Mean (± 1 ) numbers of active nests of feral Rock Doves at the study colony, 1991-1994. Sample size given for each month is the number of days on which a nest census was conducted. dates [using an incubation period of days (Johnston 1992) and a fledging period of 35-37 days (Cramp 1985)]. An active nest was scored as suc- cessful once it contained at least one chick thought to be capable of flight. Fewer censuses were made during the summer months once the low number of occupied nests became apparent. Additional notes were kept of any human disturbance, supplementary feeding of feral Rock Doves in the immediate vicinity, or of poten- tial egg predators. The majority of birds in this colony were of the grey ("wild-type") morph, and because none of these birds was banded or marked in any way we were unable to investigate move- ments of individuals or turnover rates of adults at specific sites. The area beneath each occupied nest was searched regularly for eggshells. Eggshells were rinsed in tap water to remove any lipid and albumen and stored at room temperature for 1-2 months. Six measurements of shell thickness were made for each of the failed, unhatched eggshells by sampling small (approximately 4mm x 6mm) pieces of shell with membranes attached from the equator region. Hatched eggshells were distinguished from unhatched ones by the separation of membranes and shell, which occurs during the hatching process. Statistical methods follow those of Sokal and Rohlf (1981). The term significant is used in its sta- tistical sense only, significance being accepted at the P = level. For the purpo
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