Table 2.

A tracked sample of northern gannets and indices to measure how well the sample each year represents the 50 % home range (HRA) and the 95 % core foraging area (CFA) of the entire population (~10,000 birds)

Year		Number of birds	Number of trips recorded per bird	CFA a	HRA a	CFA b	HRA b	CFA Km2	HRA Km2	Prop. of total CFA sampled	Prop. of total HRA sampled	No. of individuals needed to represent 95 % of CFA	No. of individuals needed to represent 95 % of HRA	P	NAO June
2011	Sample	17	2.2	6987	21,871	35.7	14.4	2254	11,823	0.32	0.54	633	267	na	−1.15
	Population	10,000						6962	21,840
2013	Sample	15	4.8	6175	30,010	14.8	8.5	3103	19,126	0.50	0.63	274	160	0.51	0.59
	Population	10,000						6166	29,989
2014	Sample	13	6.4	5455	25,647	11.7	8.2	2874	15,683	0.53	0.61	217	155	0.61	−0.58
	Population	10,000						5449	25,627
2015	Sample	15	6.4	7026	34,830	10.2	6.9	4287	24,296	0.61	0.70	191	130	0.48	0.17
	Population	10,000						7019	34,803

a is the asymptote value (i.e. the predicted size of the CFA/HRA for the entire population), b is the value of x (i.e. the number of individuals) at which half of the maximum response is attained and both are derived from the Michaelis–Menton equation. P is reproductive success, and the NAO index for June each year is also shown