Spatial variation in avian bill size is associated with humidity in summer among Australian passerines

Table 2 Factors affecting bill surface area of 36 species of passerine from the Meliphagoidea

	Wald statistic	Df	p-value	parameter	SE
(Intercept)	2354.543	1	<0.001	5.768	0.559
Wing Length	656.986	1	<0.001	0.01145	0.00056
SeasonCapture.autumn	49.425	3	<0.001	0	NA
.winter				−0.00958	0.00543
.summer				0.03092	0.00758
.spring				0.01419	0.00543
Sex.female	59.914	1	<0.001	0	NA
.male				0.02894	0.00423
YearCapture	10.097	1	0.001	−0.00089	0.00027
Humidity	66.511	1	<0.001	0.01802	0.00765
Tmax	0.514	1	0.473	0.00386	0.00743
Rain	0.668	1	0.414	−0.00058	0.00042
Humidity²	0.435	1	0.510	0.00048	0.0002
Tmax²	0.414	1	0.520	0.00012	0.00014
Rain²	0.239	1	0.625	6.28E-07	5.41E-07
*Humidity Tmax**	4.284	1	0.038	−0.00085	0.00027
Humidity*Rain	0.491	1	0.483	−0.00004	0.00002
*Tmax Rain**	5.250	1	0.022	0.00004	0.00002
Variance of random effects	Component	SE
Region	0.000502	0.000158
YearCapture	0.000163	0.0000821
Species	0.1485	0.0360
Residual	0.008474	0.000230

Results are from a full mixed model of bill size (log-transformed) with fixed effects of body size (wing length), season of capture, sex and all weather variables and their interactions and quadratic terms, and random effects of species, IBRA region, year and residual effect (see Model 1 in Methods). The table shows Wald statistics, df, p-values, parameter estimates and standard errors (SE). Tmax is the mean maximum summer temperature; humidity is mean summer water vapour pressure (hPa), and rainfall is mean summer rainfall, all averaged for the preceding 5 summers prior to capture; summer is defined as the months December to February. Parameter estimates for Season of Capture are relative to autumn, and for Sex are for males relative to females. Log-likelihood of model = 5102.48. N = 2864 individuals, across 41 years, 36 species and 77 IBRA regions. Significant weather terms (p < 0.05) are shown in bold

ISSN: 2053-7565