Raw data used for analysis of parental care from video footage of breeding Cape Rockjumpers (Chaetops frenatus), from the Western Cape of South Africa

Demonstrated negative effects of increased temperatures on avian
reproductive success suggest a mechanism by which climate change may
impact species persistence. High temperatures can result in reduced
parental care and reduced nestling condition in passerines with dependent
young, resulting in lowered fledging success and population recruitment.
We examined provisioning rate and nestling condition in a South African
mountain endemic, the Cape Rockjumper Chaetops frenatus, whose population
declines correlate with warming habitat. Our aim was to determine whether
Rockjumper reproductive success could be affected by high air
temperatures. We set up video cameras on nests at three nestling age
classes (≤ 7 days old; 8–12 days old; ≥ 13 days old) for 8 hours on 37
separate days. We successfully collected full-day footage on 25 of the 37
days (4 days with predation, 8 with equipment failure). Nestlings were
weighed at the beginning and end of each film day, barring the 4 days with
mid-day predation (N = 65 nestling measures from 33 of the 37 days).
Average mass gain across all nestlings per nest was positively correlated
with provisioning rate (0.78 g provisions-1 hr-1, CI: 0.26 – 1.30), and
provisioning rate decreased at increasing temperatures (-0.08 provisions
hr-1 °C-1, CI: -0.15 – -0.01). Daily change in mass of individual
nestlings was negatively correlated with air temperatures above a
significant temperature threshold (22.4 °C; -0.30 g °C-1, CI: -0.40 –
-0.19).  This suggests nestling energy requirements were not
being met on higher temperature days –– perhaps because nestling energy
and water demands for thermoregulation are elevated and provisioning rate
is not correspondingly maintained or increased. These results suggest that
higher temperatures negatively affect nestling mass gain. While in our
study this did not directly affect fledging rates, it may affect
post-fledging survival.