Pre-molting trips: Detrimental effect of GPS on body weight gain, returning date and blood isotopic values?

MORGENTHALER, ANNICK; BARRIONUEVO, MELINA; MILLONES, ANA; MARCHISIO, NAHUEL; FRERE, ESTEBAN

Conferencia; 11th International Penguin Conference; 2023

Biologgers are often used to study distribution of penguins at sea, but their effects on the studied birds are rarely evaluated. Many penguin species spend several weeks at sea foraging to gain weight before the molt; an energetically demanding process. Within the framework of a study on pre-molting trips of Rockhopper (Eudyptes chrysocome chrysocome) and Magellanic penguins (Spheniscus magellanicus) at Isla Pingüino, Argentina, we analyzed the effect of GPS on the weight gain, returning date and blood isotopic values, by comparing equipped with non-equipped (controls) marked birds. The weight gained by equipped Rockhoppers was 70% lower than that of controls (median gain: 7.9% vs 26.7%, N:16 and 17; p<0.001). Their trips were 52% longer and they returned 15 days later (median: 44 vs 29 days, N:13 and 10, p=0.005). The equipped Magellanics gained 29% less weight than controls  (median gain: 28.6% vs 40.5%, N:13 and 14; p=0.055)  and their median returning date was 18 days later (p=0.002). Within both species, the equipped and control birds had similar δ15N and δ13C values (p>0.1). Overall, we found possible adverse effects of GPS on returning dates in both species and on weight gain in Rockhoppers. This gain is of vital importance during pre-molting period since poor conditions can compromise the survival during the molt. Our results highlight the need to evaluate biologger effects when planning studies using GPS on penguins. Furthermore, our results also call into question the interpretation of published studies on penguins based on several weeks of duration GPS deployments.Ver libro de resúmenes adjunto p.157