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.

Keywords: climate; environmental cues; long-term study; phenology; reproductive performance.

Figure 1.

Variation in mean monthly snow depth (a,b), and mean monthly average daily temperatures (°C) (c,d), at two elevational sites at Sagehen Experimental Forest, CA, USA.

Figure 2.

Mean average, minimum and maximum daily temperatures (°C) in (a) April and (b) May at two elevational sites at Sagehen Experimental Forest, CA, USA from 2013 to 2022.

Figure 3.

Variation in breeding parameters across years for mountain chickadees at low and high elevations at Sagehen Experimental Forest, CA, USA: (a) first egg date; (b) clutch size; (c) brood size; (d) mean nestling mass; (e) coefficient of within-nest variation in nestling mass (CV). The mean values are shown as large black dots, the raw data are shown as small black dots and the distributions of the raw values are shown in purple for low elevation and orange for high elevation.

Figure 4.

Climatic predictors of variation in breeding parameters at low elevation. Relationships between: (a) maximum daily temperatures (°C) in autumn and first egg date; (b) snow water equivalent (mm) in autumn and brood size; (c) minimum daily temperatures in December (°C) and log-transformed coefficient of within-nest variation in nestling mass (CV); and (d) mean soil moisture measured at 5 cm depth (%) from late September to late October and log-transformed CV. Raw data are displayed as purple points, means are displayed as black points and model fit line with 95% confidence intervals are included.

Figure 5.

Climate predictors of variation in breeding parameters at high elevation. Relationships between: (a) snow depth from early February to mid-May and first egg date; (b) precipitation accumulation (mm) in March and first egg date; (c) average daily temperatures (°C) from late March to late May and clutch size; (d) minimum daily temperatures (°C) from late October to mid-November and clutch size; (e) average daily temperatures (°C) from late March to late April and brood size; (f) minimum daily temperatures (°C) from late March to late April and brood size; and (g) maximum daily temperatures (°C) from late March to late April and brood size. Raw data are displayed as orange points, means are displayed as black points and model fit lines with 95% confidence intervals are included.