Fertile period and clutch size in the Emu (Dromaius novaehollandiae)

Abstract

We tested whether female Emus lay fertilised eggs for a prolonged period, defined as the 'fertile period', following artificial insemination (AI) and natural mating (NM), and if so, whether the duration for which fertilised eggs are laid corresponds with the length of the period over which a clutch is laid. To determine the clutch duration, we studied the egg-laying pattern of AI females by recording oviposition and estimating oviposition interval. To determine the fertile period in NM females, we removed their male partners for 15 days and placed them in adjacent pens. The NM females laid fertilised eggs for a median duration of 11 days (range 7-14) after removal of males. For the fertile period after AI, the experiment was replicated 3 times. The mean fertile period of AI females was 16.2 ± 1.3 days, but maximum fertility was guaranteed for only 9 days. The AI females laid 6.7 ± 1.6 eggs per clutch and the oviposition interval within the clutch was 3.0 ± 0.1 days. The fertile period, estimated from the clutch size and egg interval, was 20.1 days. In conclusion, female Emus lay fertilised eggs for a prolonged time following an insemination, but their fertile period appears to be shorter than the period over which the clutch is laid.