Table 2.

A mixed effects model (REML) showing the relationship between provisioning rate and brood size, partner-provisioning rate, playback of begging calls and parental sex. (Nest identity was included as a random factor. The change in AIC values was calculated by fitting models using maximum likelihood. Change in AIC values for the minimal model represent AIC value of model without the term; a greater negative value therefore indicates a better contribution to model fit. Change in AIC values for the full model shows the change in AIC value with the term added, so a greater negative value indicates a negative impact on model fit. All continuous variables were standardized as described in the text. All two-way interactions were investigated; all significant interactions are reported as well as non-significant interactions of interest. p values are given for continuous variables, although in all cases an AIC value of more than 2 is accepted as significant. For factor ‘year’ results are given in contrast to those for 1999, and for ‘sex’, results are given for males in contrast to females. (N=45 individuals at 45 nests, with one, two or three treatments at each nest. There was significant repeatability of provisioning rate within nests (ΔAIC=−22.23, p<0.001).).)

	β	lower confidence limit	upper confidence limit	change in AIC	p
minimal model
intercept	0.29
brood size	0.42	0.23	0.57	−13.85	<0.001
partner prov. rate×year	−0.50	−0.79	−0.25	−6.60	significant
	−0.01	−0.34	0.27
playback	0.12	0.04	0.19	−2.90	0.001
sex	−0.39	−0.67	−0.13	−2.43	0.004
partner prov. rate	0.55	0.32	0.85	0.02−14	<0.001
year	−0.07	−0.41	0.29	2.56	n.s.
	−0.12	−0.50	0.27
terms dropped from model
hatch date	−0.07	−0.42	0.21	1.40	0.68
sex (male)×brood size	−0.07	−0.30	0.14	−1.37	0.52
partner prov. rate×brood size	−0.04	−0.18	0.10	−1.50	0.60
brood size×playback	−0.04	−0.13	0.05	−1.10	0.39
sex (male)×playback	−0.05	−0.20	0.09	−1.19	0.47
partner prov. rate×playback	0.01	−0.07	0.08	−1.51	0.94
sex (male)×partner prov. rate	−0.09	−0.42	0.22	−0.79	0.60