Nest initiation and flooding in response to season and semi-lunar spring tides in a ground-nesting shorebird

Table 2 Temporal variation in nest initiation

		Response - # of initiated nests	Gaussian			Poisson
Model	Effect type	Effect	Estimate	95% CI		Estimate	95% CI
Complex	Fixed	Intercept	0.943	0.64	1.247	−0.302	−0.591	−0.02
		Spring tide cycle number	−0.195	−0.325	−0.065	−0.236	−0.375	−0.105
		Cos (Day of spring tide cycle)	0.105	0.002	0.208	0.096	−0.016	0.202
		Sin (Day of spring tide cycle)	0.043	−0.09	0.174	0.038	−0.103	0.176
		Cos × Spring tide cycle number	−0.06	−0.163	0.041	−0.048	−0.168	0.069
		Sin × Spring tide cycle number	0.016	−0.122	0.147	0.019	−0.127	0.168
	Random (variance)	First or second half : Spring tide cycle : Year (intercept)	9%			29%
	Random (variance)	Spring tide cycle : Year (intercept)	7%			19%
		Year (intercept)	13%			40%
		Residual – Gaussian/Observation (intercept) - Poisson	71%			12%
Simple	Fixed	Intercept	1.349	0.954	1.747	0.205	−0.193	0.575
		Spring tide cycle number	−0.11	−0.188	−0.034	− 0.138	−0.216	−0.059
		Cos (Day of spring tide cycle)	0.104	0.001	0.211	0.033	−0.114	0.171
		Sin (Day of spring tide cycle)	0.04	−0.098	0.17	0.108	0.002	0.214
	Random (variance)	First or second half : Spring tide cycle: Year (intercept)	9%			30%
	Random (variance)	Spring tide cycle: Year (intercept)	7%			19%
		Year (intercept)	13%			40%
		Residual – Gaussian/Observation (intercept) - Poisson	72%			12%

The posterior estimates (medians) of the effect sizes with the 95% CIs derived from a posterior distribution of 5000 simulated values generated by the ‘sim’ function in R. Variance components were estimated by the ‘lmer’ function in R. To account for non-independence of data points ‘Year’, ‘Spring tide cycle number’ within year and indication whether the nest was initiated in the ‘First or Second half’ of the spring tide cycle were fitted as random intercepts. Overdispersion was modelled by adding ‘Observation’ level as random intercept. ‘Spring tide cycle number’ is standardized within the year, so that the first spring tide cycle in the given year corresponds to the cycle when the first nest was initiated. ‘Day of spring tide cycle’ was transformed to radians (2 * number of days after the last spring tide * π/length of the given spring tide cycle [~ 14.75]) and fitted as sine and cosine of radians

ISSN: 1742-9994