The breeding ecology of the Iberian subspecies of the Eurasian
bullfinch, Pyrrhula pyrrhula iberiae, is addressed for the first time.
The studied population occupied a hedgerow habitat in northwestern
Spain. Individuals directly watched in the study area and
details of these sightings were recorded over a six-year period,
and a total of 56 nests were monitored. The earliest date of nest
building was within 11–30 April for all years. Fledglings were
recorded leaving the nest during all the ten-day periods from the
end of May to mid-August. Nest attendance, from the early building
stage to when nestlings were ready to leave the nest, lasted
approximately 36 days. The overall mean clutch size was 4.56
eggs. Clutch size decreased significantly at the end of the breeding
season. For all egg traits, the minimum values for standard deviation
were obtained in the intra-clutch analysis, and egg length was
more variable than width. Nesting success increased progressively
from April–May to June–July and August. The main proximate
cause of nest failure was egg desertion/predation, followed by
nest desertion during nest building and nestling desertion/predation.
Mammals were the main agents in nests where the probable
predator could be identified. Approximately half of the eggs
became fledglings leaving the nest, no significant seasonal differences
being observed for this parameter. In August, the ratio of
juveniles to adults was 2.5–4.1, juveniles representing approximately
70–80% of the individuals seen and identified that month.
The absence of significant interannual variation in important reproductive
parameters could have been due to lack of interannual
variation in the availability of food resources. Compared to other
subspecies, mean clutch size of Iberian bullfinches is the smallest
recorded in the western Palearctic, and they showed an earlier start
to the breeding season and shorter mean egg length than North
European and Russian populations.