Adjustments to the timing of reproduction in response to snow cover and
spring temperature varied by species (Fig. 2; Table 3). The four species
arrived at the Colville River Delta earlier with advancing snow melt
(Fig. 2a), but this relationship was only significant for semipalmated
sandpipers (0.55 days earlier arrival for each day of advancing
snowmelt; Table 3). Earlier snowmelt resulted in a reduced pre-lay
period for brant (Fig. 2c; Table 3) and earlier nest initiation for all
four species (Fig. 2e), although the magnitude of the effect varied
among species and was greatest in brant and snow geese (Table 3). For
assessments of reproductive investment, earlier snowmelt resulted in
larger clutches for brant and snow geese (Fig. 3a; Table 3) and
increased nesting efforts by semipalmated sandpipers (Fig. 3c; Table 3).
In general, the effect of spring temperatures on reproductive phenology
and investment were less pronounced than snow cover. Warmer spring
temperatures resulted in earlier nest initiation for brant and snow
geese (Fig. 2f; Table 3), and larger clutch sizes for brant (Fig. 3b;
Table 3) and increased nesting efforts for semipalmated sandpipers (Fig.
3d; Table 3). Spring temperature did not influence any of the
reproductive metrics for longspurs (Fig. 2 and 3, Table 3).
TABLE 3 Response of black brant (BLBR), lesser snow geese
(LSGO), semipalmated sandpipers (SESA), and Lapland longspurs (LALO) to
snow cover (a; date of 50% snow cover each year) and temperature (b;
accumulated thaw-degree days from 1 January–10 June each year),
2011–2018, Colville River, Alaska. Values represent statistically
significant slope parameters (±95% confidence intervals) from linear
least-squares regression models with date of site arrival, duration of
pre-lay period, date of nest initiation, clutch size, and number of
nests as response variables. There was no support for species-specific
differences in site arrival or pre-lay duration as a function of
temperature, but all other assessments had at least one significant
species-specific response. Significance levels represented by *
(P ≤ 0.05), ** (P ≤ 0.01), and *** (P ≤ 0.001);
n.s. indicates P > 0.05