Table 3 Results from models (after backward selection) investigating how life history traits and body mass varied across the three study sites.

Response variable
Explanatory variable	Estimate	Std. Error	z value	P value
(a) Lay date (poisson GLM)
Intercept	3.47	0.05	72.17	<0.001
(b) Clutch size (poisson GLM)
Intercept	2.59	0.18	14.17	<0.001
Lay date	−0.01	0.01	−2.33	0.020
(c) Hatch date (poisson GLM)
Intercept	3.70	0.08	44.43	<0.001
Lay date	0.01	<0.00	4.91	<0.001
(d) Hatching success (binomial GLM)
Intercept	1.25	0.85	1.47	0.141
Site	−0.55	0.23	−2.36	0.018
(e) Fledging success (binomial GLM)
Intercept	11.43	2.03	5.62	<0.001
Site	−5.95	1.02	−5.85	<0.001
(f) Number of fledglings (poisson GLM)
Intercept	2.68	0.15	17.99	<0.001
Site	−1.01	0.10	−10.14	<0.001
(g) Nestling body mass at day 13 (LMM)
Intercept	12.11	0.35	34.26	<0.001
Site	−0.91	0.20	−4.49	<0.001
(f) Adult body mass (LMM)
Intercept	11.27	0.48	23.22	<0.001

Lay date, clutch size, hatch date and number of fledglings were modelled with a Poisson error structure, hatching success (number of hatchlings over laid eggs) and fledging success (number of fledglings over number of hatchlings), were modelled with a binomial error structure, while adult and nestling body mass were modelled with a Gaussian error structure in LMMs with nestbox included as random factor. Site was included in all models as main fixed effect, whereas date of first egg of each nest was included as covariate to control for seasonal variation in reproductive timing and body mass (except for the model testing for variation in lay date across sites). For adult body mass, sex was also included as fixed factor. These were dropped if not significant via backward selection (only significant variables are shown).

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