Incubation behaviour in a double-nesting alpine bird Alectoris graeca saxatilis: Similar nest attendance by males and females

In birds with double-nesting and uniparental incubation, such as the rock
partridge (Alectoris graeca saxatilis), the male incubates one clutch,
while the female incubates the other. A previous study found no
significant difference in hatching and predation rates on Alpine rock
partridge nests incubated by each sex. We therefore hypothesized that the
incubation rhythms of both sexes would be similar. To test this, we
monitored the incubation patterns of 40 nests incubated by females and 41
nests incubated by males in the French Alps between 2011 and 2020.
Temperature loggers were installed within and outside the nests to record
internal and ambient temperatures at 3-minute intervals. Incubation recess
timing and duration were inferred from the analysis of temperature curves.
We employed statistical modelling to assess the effects of the incubating
bird’s sex, minimum ambient temperature, incubation day, clutch size and
recess rank on various incubation parameters. The timing, total duration,
and number of recesses, as well as nest temperature, were found to be
similar between the sexes. On average, birds took 2.5 recesses per day,
with each recess lasting approximately 75 minutes. Overall nest attendance
was ≃ 88%. Recesses occurred throughout the day, with a peak after sunrise
and a second, less pronounced peak before sunset. Nocturnal recesses were
rare and resulted from disturbances to the incubating bird. Modelling
results indicated only slight differences in the mean recess duration
between the sexes throughout the incubation period. Further analysis
showed that both sexes adjusted their incubation rhythms in a similar
manner in response to the progress of incubation and to daily minimum
temperatures. Cold temperatures may compel parents to spend more time
foraging to meet their energy needs. Rock partridges exhibited lower nest
attendance compared to grouse species inhabiting cold environments, likely
due to their relatively lower body reserves.