Fit is fat: winter body mass of Atlantic Puffins Fratercula arctica

Figures & data

Figure 1. Ringing locations of 106 Atlantic puffins recovered around the Faroe Islands between October and March, as reported by December 2017. Totals for the Isle of May (38) and Røst (17) include a few birds ringed at nearby colonies. Names of study sites are indicated in bold.

Figure 2. Linear regressions (± 95% confidence intervals) of body mass as a function of wing length for adult Puffins killed in the Faroes (large white circles) in winter (October–March) and for chick-rearing adults at the colonies of Isle of May (southeast Scotland; black dots) and Røst (northern Norway; grey dots). Symbols indicate individual birds. For clarity, wing lengths of birds in the colonies are plotted 0.25 mm below (Isle of May) or above (Røst) the true values.

Table 1. Descriptive statistics of body mass and wing length for adult Puffins killed in Faroese waters in eight winters (October–March 1981–2018) and for chick-rearing adults at the colonies of Isle of May (Southeast Scotland) in 21 summers (1973–2017) and Røst (North Norway) in 34 summers (1980–2017). The sexed individuals are included in the ‘all’ categories.

Season	Locality	Wing length (mm)				Body mass (g)
		Mean	se	Range	n	Mean	se	Range	n
Winter	Faroes, all	167.9	0.54	153–180	133	540.3	8.74	390–730	54
	Faroes, males	169.2	0.92	162–178	31	545.4	14.37	390–730	28
	Faroes, females	165.2	1.31	153–176	31	532.3	9.74	438–636	22
Chick-rearing	Isle of May, all	161.1	0.12	144–176	1455	379.3	0.77	302–483	1463
	Isle of May, males	163.0	0.42	152–172	96	404.1	2.47	340–471	93
	Isle of May females	163.1	0.43	152–170	85	367.9	2.47	311–444	86
Chick-rearing	Røst, all	171.8	0.09	158–184	1950	450.0	0.69	340–585	2381
	Røst, males	172.6	0.31	164–184	157	463.0	1.93	385–555	180
	Røst, females	170.7	0.28	158–179	166	429.1	2.02	348–517	190

Table 2. Univariate GLM tests of differences in body mass between adult Puffins killed in Faroese waters in winter (October–March) and chick-rearing adults at the colonies of Isle of May (southeast Scotland) and Røst (northern Norway), respectively, when controlling for differences in body size by entering wing length as a covariate.

Parameter	All sites			Faroes vs. Isle of May			Faroes vs. Røst			Isle of May vs. Røst
	Fdf,3429	df	P	Fdf,1491	df	P	Fdf,1982	df	P	Fdf,3384	df	P
Intercept	14.09	1	< 0.001	25.92	1	< 0.001	0.317	1	0.573	17.33	1	< 0.001
Year	40.37	1	< 0.001	57.76	1	< 0.001	0.488	1	0.485	39.77	1	< 0.001
Wing	177.6	1	< 0.001	77.96	1	< 0.001	94.25	1	< 0.001	888.0	1	< 0.001
Site	11.12	2	< 0.001	0.704	1	0.402	0.138	1	0.711	22.97	1	< 0.001
Wing*Site	16.07	2	< 0.001	3.33	1	0.068	0.070	1	0.791	32.32	1	< 0.001
Full model	1184.2	6	< 0.001	491.1	4	< 0.001	222.0	4	< 0.001	1650.6	4	< 0.001

Table 3. Estimated differences in mean body mass between adult Puffins killed in Faroese waters in winter (October–March) and chick-rearing adults of the same size (as indicated by wing length) at the colonies of Isle of May (southeast Scotland) and Røst (northern Norway), respectively. The results are based on the estimated marginal means from the corresponding pairwise GLM analyses reported in Table 2.

Samples compared	Wing length for comparison (mm)	Summer mass (g)		Winter mass (g)		Summer to winter difference [%]
		Mean	se	Mean	se
Faroes vs. Isle of May	161.4	380.0	0.712	497.7	7.11	+ 117.7 g [31.0%]
Faroes vs. Røst	171.7	451.2	0.688	545.0	4.96	+ 93.8 g [20.8%]

Table 4. Body mass (g) and wing length (mm) of three Atlantic puffins that were weighed as adults both at the colony in the chick period and when killed in Faroese waters in winter (October–March).

Colony	Bird ring ID	Summer data		Winter data			Summer to winter difference [%]
		Date	Mass	Date	Wing	Mass
Røst	NOO MA10529	26.6.1983	505	10.12.1990	171	560	+ 55 g [10.9%]
Runde	NOS 5174113	11.7.2007	480	18.11.2008	173	636	+ 156 g [32.5%]
Isle of May	BTO EY52113	17.7.2013	409	26.10.2017	165	520	+ 111 g [27.1%]