The breeding behaviour of crimson rosellas
(Platycercus elegans) in Canberra, Australia, was
studied between 1993 and 1996. Female rosellas initiated breeding in late
September or early October, laying a mean of 5.3 ± 0.1 (s.e.) eggs at
1–4-day intervals. Of all eggs laid, 50% fledged successfully.
Rosellas had the highest breeding success in the wettest year (1995), when
they bred earlier, laid larger clutches and fledged more young. Unexpectedly,
breeding success was not lowest in the driest year (1994), although fewer
birds attempted breeding and hatching success was low. In this study, poor
environmental conditions for breeding were counterbalanced by decreased levels
of conspecific interference through egg destruction. Overall, 55.8% of
all clutches initiated were destroyed during laying, and more than half of
this was attributed to rosellas. The reasons for egg destruction by rosellas
were not clear. Boxes where clutches were destroyed were not quickly
reoccupied and egg destruction was not highest when competition for nesting
hollows was most intense. Clutch size and egg-laying intervals decreased over
the breeding season, but the length of incubation did not. Large clutches did
not produce more fledglings, because more eggs failed to hatch, especially
early in the season. Eggs in a clutch hatched over a period of 0.5–7
days. Total hatching asynchrony increased over the breeding season and was not
strongly correlated with clutch or brood size. This suggests that female
rosellas initiated incubation at different times during laying. Clutches with
longer hatching intervals took longer to incubate. If females in poor
condition are inefficient incubators, female condition may affect the degree
of hatching asynchrony.
Physical characteristics and reproductive performance in Aedes (Diptera: Culicidae)