Table 5.

Only invertebrate‐fed common bulbuls Pycnonotus barbatus decrease in body mass with increased immune function. Relationship between body mass and variation in PC1 (decreasing haptoglobin concentration and increasing haemolysis titre), PC2 (increasing ovotransferrin concentration and haemagglutination titre) and PC3 (increasing nitric oxide concentration) in common bulbuls fed on fruits or invertebrates. Each individual was sampled before diet treatment and then subsequently, fortnightly over a 24‐week period. Week was included to account for temporal variation in environmental factors. Individual identity and diet switching history were included as random effects to control for individual variability and treatment switch effects respectively

Factor	PC1			PC2		PC3
	Haptoglobin and haemolysis			Ovotransferrin and haemagglutination		Nitric oxide
	df	Chisq	p	Chisq	p	Chisq	p
Samplinga	1	10.57	<.01**	7.62	<.01**	8.99	<.01**
Captureb	1	8.56	.01**	5.41	.02*	6.13	.01*
Sex	1	26.74	<.01***	25.29	<.01***	24.88	<.01***
Immune function	1	7.68	<.01**	0.51	.47	0.04	.84
Diet	1	20.03	<.01***	12.84	<.01***	12.95	<.01***
Week (0–24)	11	292.92	<.01***	323.57	<.01***	315.06	<.01***
Immune function*Diet	1	5.56	.02*	7.04	<.01**	0.38	.54

^aSampling—time lag between capture and sampling.

^bCapture—time lag between the first capture of each day and the sampling of each bird.

Statistically significant effects are highlighted bold.

*p < .05, **p < .01, ***p < .001.