Table 1. Discrimination factors Δ δ¹³C and Δ δ¹⁵N between food and various tissues of four herbivorous Anatidae species.

Source	Tissue	Δ δ13C	t-test	Δ δ15N	t-test	nx, ny
Food to:	Plasma	0.3±0.52A,B	1.52	4.4±0.62A,B	4.69*	9, 9
	Blood cells	−0.5±0.62A,B	1.59	3.6±0.52A,B	0.71	9, 9
	Claw	0.4±0.58A,B	0.56	4.5±0.67A,B	1.09	9, 9
	Back feather	1.0±1.03A,B	2.91*	4.7±0.71A,B	1.06	9, 9
	Primary feather	0.9±0.73A,B	1.73	5.2±0.56A,B	1.87	9, 9
Dropping to:	Yolk	2.5±0.81D	-	2.8±2.73D	-	4
Yolk to:	Down feather	−1.1±0.44C,D	2.55*	1.9±0.51C,D	2.27*	9, 10
Albumen to:	Down feather	−0.9±0.61C,D	0.27	2.7±1.29C,D	1.17	9, 10

Source -tissue discrimination was measured experimentally in captive Bewick Swans Cygnus columbianus bewickii (A) and mallards Anas platyrhynchos (B); diet and egg tissue- feather discrimination was determined in free-living Barnacle Geese Branta leucopsis (C) and Pink-footed Geese Anser brachyrhynchos (D). Herein, droppings were used as proxies for ingested food. Between-species differences were examined with t-test,

*marks a difference at p-level<0.05, n^x gives sample size for the respective species. Individual species values are provided in Table S2.