Behavioural thermoregulation in man-made habitats: surface choice and mortality risk in Red-necked Nightjars

Figures & data

Table 1. Seasonal variation in Red-necked Nightjars' occurrence on the road network crossing the study area (paved and gravel roads together), with number of road casualties at the regional scale (which represents the proportion of all casualties that occurred during each month) and mean daily air temperatures at the study site. Values are reported as means ± se.

Month	Road occurrence (birds/km)	Birds/km gravel roads	Birds/km paved roads	Road casualties (%)	Air temperature (°C)
April	0.28 ± 0.07	0.25 ± 0.10	0.35 ± 0.19	18.1 (n = 56)	17.6 ± 0.3
May	1.74 ± 0.17	1.63 ± 0.23	1.95 ± 0.49	28.5 (n = 88)	20.7 ± 0.4
June	2.03 ± 0.08	2.03 ± 0.14	2.06 ± 0.26	5.8 (n = 18)	23.7 ± 0.5
July	1.34 ± 0.18	1.37 ± 0.27	1.25 ± 0.53	7.8 (n = 24)	24.5 ± 0.3
August	2.17 ± 0.16	2.54 ± 0.22	1.64 ± 0.17	8.4 (n = 26)	25.7 ± 0.3
September	1.65 ± 0.19	1.58 ± 0.17	1.50 ± 0.24	19.1 (n = 59)	22.4 ± 0.2
October	0.39 ± 0.09	0.31 ± 0.09	0.54 ± 0.15	12.3 (n = 38)	19.1 ± 0.2

Table 2. Multiple regression model (GLM with normal distribution for errors and an identity link function) testing the effect of environmental cues on road surface use by Red-necked Nightjars. The ratio between birds/km on gravel and paved roads is included as the dependent variable. Significant values (P < 0.05) are highlighted in bold.

Variable	Estimate	se	d.f.	t	P
Air temperature (°C)	0.043	0.015	1,50	2.96	0.005
Rainfall (Y/N)	–0.307	0.175	1,50	–1.76	0.086
Relative humidity (%)	–0.007	0.005	1,50	–1.35	0.184
Moonlight (% visible disk)	–0.213	0.167	1,50	–1.28	0.209

Figure 1. Seasonal variation in road surface use by Red-necked Nightjars at the study site. Bars show the relative occurrence (with standard errors of the mean) of birds on gravel and paved roads. Values >1 and <1 indicate Nightjars concentrating on gravel and paved roads, respectively.

Figure 2. Effect of air temperature on surface use by Red-necked Nightjars at the study site. Shaded and open areas illustrate the use of paved and gravel roads, respectively.