Complex relationships between climate and reproduction in a resident montane bird

Abstract

Animals use climate-related environmental cues to fine-tune breeding timing and investment to match peak food availability. In birds, spring temperature is a commonly documented cue used to initiate breeding, but with global climate change, organisms are experiencing both directional changes in ambient temperatures and extreme year-to-year precipitation fluctuations. Montane environments exhibit complex climate patterns where temperatures and precipitation change along elevational gradients, and where exacerbated annual variation in precipitation has resulted in extreme swings between heavy snow and drought. We used 10 years of data to investigate how annual variation in climatic conditions is associated with differences in breeding phenology and reproductive performance in resident mountain chickadees ( Poecile gambeli ) at two elevations in the northern Sierra Nevada mountains, USA. Variation in spring temperature was not associated with differences in breeding phenology across elevations in our system. Greater snow accumulation was associated with later breeding initiation at high, but not low, elevation. Brood size was reduced under drought, but only at low elevation. Our data suggest complex relationships between climate and avian reproduction and point to autumn climate as important for reproductive performance, likely via its effect on phenology and abundance of invertebrates.

Relative breeding timing and reproductive success of a resident montane bird species

“…Clutch size was recorded at the onset of incubation. Fledgling body mass and brood size were recorded on day 16 post-hatch (fledging time varies between day 20-24 post-hatch, but day 16 is early enough to prevent force-fledging when processing the young) when all nestlings were weighed to the nearest 0.1 g and banded with a unique numeric aluminium band issued by the United States Geological Survey Bird Banding Laboratory [45,46]. We check nest boxes after birds leave the nest to clean boxes for the next season and we do not typically observe any dead nestlings that were alive at day 16 but died before fledging, so we use the number of young at day 16 (brood size) as a measure of the number of successful fledglings.…”

“…High and low elevations were modelled separately as metrics of reproduction vary with elevation (e.g. high-elevation birds start breeding 2-3 weeks after low-elevation birds and generally have larger clutches and broods), and we expected divergent responses across elevations owing to differences in climate [45,46]. We modelled the effect of relative timing (three categories-early, peak and late) on clutch size, brood size, mean fledgling mass and within-nest CV in fledgling mass separately with linear mixed-effects models using the 'glmmTMB' package [54], including year as a random effect.…”

“…In montane systems, environmental conditions change rapidly along elevation gradients (e.g. [45]), presenting the opportunity to examine fitness consequences of reproductive timing of a single population under different levels of environmental harshness. We have studied mountain chickadee reproduction in nest boxes for 11 years (2013-2023) at two distinct elevational sites: 'low' (range: 1965−2070 m) and 'high' (range: 2380−2590 m) [45].…”

“…[45]), presenting the opportunity to examine fitness consequences of reproductive timing of a single population under different levels of environmental harshness. We have studied mountain chickadee reproduction in nest boxes for 11 years (2013-2023) at two distinct elevational sites: 'low' (range: 1965−2070 m) and 'high' (range: 2380−2590 m) [45]. These two elevational bands vary in climate, mostly driven by differences in overwinter snow accumulation (high elevation accumulates much more snow than low elevation, and snow at high elevation persists longer into the summer) [45].…”

“…We have studied mountain chickadee reproduction in nest boxes for 11 years (2013-2023) at two distinct elevational sites: 'low' (range: 1965−2070 m) and 'high' (range: 2380−2590 m) [45]. These two elevational bands vary in climate, mostly driven by differences in overwinter snow accumulation (high elevation accumulates much more snow than low elevation, and snow at high elevation persists longer into the summer) [45]. Our previous work showed that at high, but not low elevation, breeding timing was associated with spring snow accumulation (later breeding in years with more snowfall) while yearly variation in spring temperature was not associated with reproductive phenology at either elevation [45].…”