Daily survival rate.
All years. The first round of model building included temporal
variables with nests from all years (2016, 2018, 2019, 2021; NOCC=63;
Table 2). Daily survival probability for Swainson’s thrush across the
four-year sampling period was 23%. We did not find support that
elevation affected daily survival probability (b =0.0005, 95% CI
[-0.0008, 0.0019], 90% CI [0.0017, -0.0005]). The model with
the most support suggested that nests have a higher probability of
failing as the season progresses (Table 2; b =-0.02, 95% CI
[-0.05, 0.0092]). When we examined linear time within 90%
confidence intervals, the model suggests some support (b =-0.02,
90% CI [-0.003, -0.051]). We examined all models using AIC and
found two models that were within 2 ΔAICc values of one another and
demonstrated the strongest support above the null model, which were the
quadratic time trend and linear time trend (Table 3). Finally, we ran an
interaction effect between time and elevation (b = -0.00004, 95%
CI [-0.0001, 0.00006]) but this model did not perform well and was
removed from our model comparison output.
2019 and 2021. In the second stage of our analysis, we built
models for nests from 2019 and 2021 (Table 2) and included temperature
and precipitation covariates, as well as effects with initiation date
against daily survival rate. There was no evidence that nest survival
was affected by either initiation date (b = -0.007, 95% CI
[-0.047, 0.032]) or elevation (b = 0.0003, 95% CI [-0.0009,
0.0016]). Nest survival was negatively related to linear time
(b =-0.03, 90% CI [-0.002, -0.057]), indicating some support
that nest survival declined over the 2019 and 2021 nesting season.
We ran an interaction effect between elevation and several other
meaningful parameters, including initiation date (b = -0.00003,
95% CI [-0.0001, 0.00008]), linear time (b = -0.00003, 95%
CI [-0.0003, 0.00006]) and nest age (b = 0.00004, 95% CI
[-0.00008, 0.00016]) but we did not find support for these
relationships. We also included an interaction between linear time and
year (Table 1, model 15) because precipitation varied markedly among
years (Fig. 1A&B), and we were interested in evaluating year for other
interannual variation, but this relationship did not demonstrate an
effect (Table 2; b = -0.002, 95% CI [-0.07, 0.06]).
Environmental covariates (2019 and 2021 only). Our models did not
show support that average daily temperature (b = -0.02, 95% CI
[-0.15, 0.11]), minimum daily temperature (b = -0.02, 95% CI
[-0.13, 0.08]) or daily temperature range (b =0.06, 95% CI
[-0.04, 0.16]) affected daily nest survival in Swainson’s thrush
(Table 2). We found strong support that an interaction between elevation
and minimum daily temperature effected daily survival rate (b =
-0.007, 95% CI [-0.001, -0.0002]). We also found strong support for
an interaction between elevation and average daily temperature
(b = -0.0006, 95% CI [-0.001, -0.000009]). Because our other
temperature variable (i.e., daily temperature range) demonstrated
collinearity with elevation, we did not test interaction effects of
these relationships.
We examined “light” and “heavy” rain events and found support that
light rain (i.e., 0-6.9mm) negatively affected the daily survival rate
of Swainson’s thrush nests (b = -1.39, 95% CI [-2.72,
-0.05]) but we did not find an effect of “heavy” rain events
(>7mm; b = 3.51, 95% CI [-144.70, 151.73])
(Table 2). We further investigated our rain metrics by quantifying rain
intensity as millimeters per hour and found a strong negative
relationship on daily survival rate (b =-0.09, 95% CI [-0.18,
-0.01]; Figure 3). We did not find an effect of cumulative daily
precipitation on daily nest survival probability (b = 0.01, 95%
CI [-0.09, 0.11]). We did not find any support for an interaction
effect between rain intensity and cumulative daily precipitation
(b = 0.004, 95% CI [-0.02, 0.03]), rain intensity and nest
age (b = 0.003, 95% CI [-0.007, 0.015]), and elevation and
rain intensity (b = -0.00005, 95% CI [-0.0007, 0.0006]).
In the final stage of our analysis for nests from 2019 and 2021, we
compared models of interest using AIC. This revealed two competing
models against DSR, the most parsimonious model to be the interaction
between elevation and minimum daily temperature against daily survival
rate (Table 3). We found some support for the second most competitive
model, suggesting that as rain intensity increases, the daily survival
rate of Swainson’s thrush decreases (Δ AICc <4; Table
3), though it should be noted that this model was within 2Δ AICc values of the null model.