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Table 1 The results of linear mixed models analysing the effects of a set explanatory variables on body mass and tarsus length of 14-day-old offspring

From: The interactive effect of ambient temperature and brood size manipulation on nestling body mass in blue tits: an exploratory analysis of a long-term study

Model

Estimate (SE or CIs)

d.f

F

P

Offspring body mass (N = 2690)

    

Intercept

10.84 (0.06)

   

Treatment

0.25 (0.06)

1, 451.2

19.98

 < 0.001

Offspring sex

0.22 (0.03)

1, 2454.4

72.99

 < 0.001

Temperature

2.01 (0.70)

1, 109.6

1.04

0.31

Temperature2

− 2.01 (0.70)

1, 99.2

0.95

0.33

Hatching date

0.09 (0.04)

1, 31.6

4.64

0.039

Body mass on day 2

0.26 (0.02)

1, 2513.4

281.20

 < 0.001

Tarsus length

0.42 (0.02)

1, 2634.8

641.03

 < 0.001

Treatment × temperature

2.82 (0.83)

1, 369.0

11.72

 < 0.001

Treatment × temperature2

2.89 (0.82)

1, 363.9

12.38

 < 0.001

Female identity

0.31 (0.25, 0.36)

   

Foster female identity

0.51 (0.45, 0.57)

   

Year

0.11 (0.00, 0.20)

   

R2marginal/conditional

0.36/0.71

   

Offspring tarsus length (N = 2694)

    

Intercept

16.10 (0.07)

   

Treatment

0.09 (0.04)

1, 478.6

4.10

0.043

Offspring sex

0.41 (0.02)

1, 2400.0

519.16

 < 0.001

Temperature

0.86 (0.45)

1, 261.2

3.60

0.059

Temperature2

− 0.83 (0.46)

1, 219.3

3.30

0.071

Body mass on day 2

0.18 (0.01)

1, 2587.9

245.42

 < 0.001

Female identity

0.26 (0.22, 0.31)

   

Foster female identity

0.33 (0.28, 0.37)

   

Year

0.18 (0.09, 0.28)

   

R2marginal/conditional

0.17/0.61

   
  1. Full models (see Additional file 1: Table S2) included treatment (the level of this factor refers to enlarged nests) and offspring sex (the level of this factor refers to males) as categorical fixed factors, temperature and precipitation (both as linear and quadratic terms), hatching date, brood size, body mass on day 2 and tarsus length (only in body mass analysis) as covariates (all centred and standardised). Interactions between treatment and climatic variables were also tested. In all models, female identity, foster female identity and the year of study were random factors. Presented are reduced (final) models, with determined marginal and conditional R2, after the backward elimination of non-significant (if P > 0.1) interactions and covariates. Estimates of fixed and random factors are accompanied with SE and CIs, respectively. Significant terms (P < 0.05) are in bold