Behavioural responses of non-breeding waterbirds to marine traffic in the near-shore environment

Figures & data

Figure 1. Routes on which recording of behavioural responses to the passing ferry was carried out. Route A: Houton – Lyness – Flotta; Route B: Kirkwall – Shapinsay; Route C: Tingwall – Rousay – Wyre – Egilsay.

Figure 2. Summary of all responses by birds to a passing ferry. Number of records for each species is shown in parenthesis on the x-axis. Species are ordered from left to right in order of proportion of flocks responding.

Table 1. Summary of species-specific response models. The ‘All responses’ models used flight, swim and dive responses in the response variable, while the ‘flight response’ modes only included flight responses. ‘Scapa Flow’ is the effect of data gathered in Scapa Flow compared to the reference level, North Orkney (see Figure 1). For Slavonian Grebe and Black-throated Diver all records were in Scapa Flow so there is no covariate shown. No Black-throated Diver flights were recorded so no flight model is shown. Statistically significant (P < 0.05) results are shown in bold. For the ordered categorical variables (sea state and distance band) the linear effect is shown, and quadratic effects are only shown where P < 0.05.

		All responses models				Flight responses models
Species	Covariate	Effect size	Std. error	z value	P value	Effect size	Std. error	z value	P value
Common Eider	Intercept	−1.42	0.14	−10.32	< 0.01	−2.91	0.21	−14.03	< 0.01
	Distance band (l)	−3.06	0.19	−16.01	< 0.01	−1.96	0.28	−7.04	< 0.01
	Sea state (l)	−0.13	0.37	−0.35	0.73	1.27	0.55	2.30	0.02
	Flock size (ln)	0.35	0.06	5.59	< 0.01	0.25	0.08	2.98	< 0.01
	Scapa Flow	0.40	0.13	3.11	< 0.01	0.36	0.17	2.06	0.04
	Time of year	0.09	0.06	1.45	0.15	0.21	0.10	2.16	0.03
Long-tailed Duck	Intercept	−0.28	0.16	−1.72	0.09	−1.33	0.17	−7.67	< 0.01
	Distance band (l)	−2.62	0.22	−12.11	< 0.01	−2.30	0.22	−10.51	< 0.01
	Distance band (q)	0.41	0.19	2.19	0.03	0.13	0.19	0.68	0.50
	Sea state (l)	−0.24	0.19	−1.29	0.20	−0.01	0.10	−0.09	0.93
	Flock size (ln)	−0.08	0.09	−0.89	0.37	0.74	0.20	3.68	< 0.01
	Scapa Flow	0.37	0.20	1.87	0.06	0.09	0.09	0.98	0.33
	Time of year	0.18	0.09	1.95	0.05	−1.33	0.17	−7.67	< 0.01
Red-breasted Merganser	Intercept	0.09	0.40	0.21	0.83	−0.42	0.41	−1.02	0.31
	Distance band (l)	−1.46	0.47	−3.11	< 0.01	−1.16	0.46	−2.52	0.01
	Sea state (l)	−0.46	0.40	−1.13	0.26	0.09	0.44	0.21	0.83
	Flock size (ln)	−0.04	0.19	−0.21	0.84	−0.42	0.22	−1.88	0.06
	Scapa Flow	0.01	0.46	0.02	0.99	−0.51	0.49	−1.04	0.30
	Time of year	−0.35	0.19	−1.83	0.07	−0.26	0.20	−1.29	0.20
Red-throated Diver	Intercept	0.06	0.54	0.11	0.91	−1.12	0.63	−1.77	0.08
	Distance band (l)	−0.07	0.55	−0.14	0.89	−0.06	0.54	−0.11	0.91
	Sea state (l)	−1.42	0.87	−1.64	0.10	−0.81	0.93	−0.87	0.38
	Flock size (ln)	−0.26	0.29	−0.90	0.37	0.26	0.68	0.38	0.71
	Scapa Flow	0.95	0.85	1.12	0.26	−0.44	0.36	−1.25	0.21
	Time of year	0.57	0.38	1.49	0.14	0.87	0.91	0.95	0.34
Black-throated Diver	Intercept	−4.47	2.90	−1.54	0.12	–	–	–	–
	Distance band (l)	1.48	1.77	0.84	0.40	–	–	–	–
	Sea state (l)	−5.14	3.41	−1.51	0.13	–	–	–	–
	Flock size (ln)	1.61	1.24	1.30	0.19	–	–	–	–
	Time of year	6.26	4.70	1.33	0.18	–	–	–	–
Great Northern Diver	Intercept	0.76	0.31	2.48	0.01	−1.77	0.44	−4.00	< 0.01
	Distance band (l)	−2.63	0.26	−10.27	< 0.01	−1.24	0.84	−1.48	0.14
	Distance band (q)	−0.17	0.23	−0.74	0.46	−1.74	0.74	−2.36	0.02
	Sea state (l)	−0.30	0.22	−1.34	0.18	0.86	0.57	1.51	0.13
	Flock size (ln)	0.18	0.12	1.59	0.11	−0.06	0.40	−0.16	0.87
	Scapa Flow	−0.84	0.33	−2.52	0.01	−3.30	0.74	−4.45	< 0.01
	Time of year	0.04	0.13	0.34	0.73	−0.60	0.41	−1.46	0.14
European Shag	Intercept	−1.13	0.14	−8.07	< 0.01	−2.01	0.18	−11.01	< 0.01
	Distance band (l)	−2.31	0.22	−10.70	< 0.01	−1.53	0.25	−6.01	< 0.01
	Sea state (l)	1.56	0.39	3.99	< 0.01	2.13	0.53	4.04	< 0.01
	Flock size (ln)	0.12	0.07	1.63	0.10	0.07	0.08	0.81	0.42
	Scapa Flow	0.05	0.17	0.27	0.79	−0.37	0.20	−1.83	0.07
	Time of year	−0.26	0.08	−3.30	< 0.01	−0.14	0.10	−1.48	0.14
Slavonian Grebe	Intercept	0.14	0.74	0.19	0.85	−0.33	0.49	−0.67	0.50
	Distance band (l)	−1.92	1.10	−1.75	0.08	−1.06	0.72	−1.48	0.14
	Sea state (l)	0.78	1.21	0.65	0.52	1.11	0.83	1.34	0.18
	Flock size (ln)	0.95	0.66	1.44	0.15	0.29	0.50	0.59	0.55
	Time of year	−0.31	0.75	−0.41	0.68	−1.63	0.89	−1.84	0.07
Black Guillemot	Intercept	−2.06	0.15	−13.33	< 0.01	−3.41	0.32	−10.77	< 0.01
	Distance band (l)	−1.80	0.22	−8.14	< 0.01	−1.75	0.50	−3.53	< 0.01
	Distance band (q)	0.59	0.21	2.85	< 0.01	0.11	0.43	0.27	0.79
	Sea state (l)	0.41	0.27	1.52	0.13	1.34	0.68	1.97	0.05
	Flock size (ln)	−0.14	0.07	−2.06	0.04	−0.16	0.13	−1.30	0.19
	Scapa Flow	0.20	0.13	1.50	0.13	−0.15	0.20	−0.76	0.45
	Time of year	−0.38	0.07	−5.64	< 0.01	−0.04	0.12	−0.33	0.74

Figure 3. Predicted likelihoods of a) any response (flush, swim or dive) and b) flight responses to the passing vessel for each species at the four distance bands (with 95% confidence intervals) from the species-specific GLMs. Other covariates are held at mean values. There were no flight responses recorded for Black-throated Diver so no flight responses plot is shown for this species.

Table 2. Summary of the combined mixed effects models for all responses and flight responses. For the ordered categorical variables ‘distance band’ and ‘sea state’, only the linear and quadratic terms are shown. The fixed effects are the same as for the species-specific models (Table 1). The variance explained by the random effects ‘species’, ‘week’ and ‘trip’ (nested in ‘week’) and Marginal and Conditional R² of each model are also shown. Statistically significant (P < 0.05) results are shown in bold.

All responses model					Flight responses model
Fixed effects
Term	Effect size	Standard error	z value	P value	Effect size	Standard error	z value	P value
Intercept	0.93	0.65	1.45	0.15	−2.17	0.64	−3.41	< 0.01
Distance band (linear)	−2.63	0.09	−29.25	< 0.01	−1.78	0.12	−15.35	< 0.01
Distance band (quadratic)	0.18	0.07	2.42	0.02	0.07	0.10	0.67	0.50
Sea state (linear)	0.33	0.32	1.04	0.30	1.38	0.38	3.62	< 0.01
Sea state (quadratic)	−0.47	0.28	−1.69	0.09	−0.50	0.35	−1.45	0.15
Time of year	−0.011	0.005	−2.37	0.02	−0.00	0.00	−0.06	0.95
Scapa Flow	0.06	0.14	0.46	0.65	0.09	0.13	0.65	0.51
Flock size	0.20	0.04	4.58	< 0.01	0.10	0.05	1.91	0.06
Random effects
Term	N	Variance	Std.Dev		N	Variance	Std.Dev
Trip:Week	116	0.20	0.44		116	0.17	0.42
Week	11	0.14	0.37		11	0.02	0.13
Species	9	1.60	1.26		9	2.18	1.48
Marginal R^2/Conditional R^2	0.253/0.529				0.150/0.505

Figure 4. Predicted likelihood of flocks flushing at different sea states with covariates held at mean values from the species-specific GLMs. Some sea state categories were combined where sample sizes were small.

Figure 5. Likelihood of responses predicted from the combined GLMM models for each species, with the ‘any responses’ model predictions on the x-axis and the ‘flight responses’ model predictions on the y-axis. Predicted likelihoods are transformed into binary space where ‘1’ is certain to respond and ‘0’ certain not to respond. All other covariates are at mean values. E = Common Eider, LN = Long-tailed Duck, RM = Red-breasted Merganser, BV = Black-throated Diver, ND = Great Northern Diver, RH = Red-throated Diver, SA = European Shag, SZ = Slavonian Grebe, TY = Black Guillemot.