Food intake, feeding rhythm, and body mass regulation in Svalbard rock ptarmigan

Abstract

Food intake (FI), feeding activity (FA), and body mass (BM) were recorded continuously throughout a 13-mo period in Svalbard rock ptarmigan kept under natural conditions of light and ambient temperature at Svalbard (79 degrees N). FI was persistently high from March until August, including the period when daylight is continuous, whereas it was low from November until January, when it is permanently dark. From August until November, BM doubled, while FI dropped to one-third. BM fell rapidly from mid-November until April despite a doubling of FI from February until March. From August until mid-November and from February until mid-April FA occurred mainly during the light period of the day. From late November until February and from mid-April until August intermittent FA occurred continuously. It is suggested that the seasonal changes in BM are not determined by FI alone but depend heavily on seasonal changes in locomotor activity as reflected in FA.

Adaptations to polar life in mammals and birds

“…However, during the continuous polar night, as well as during the continuous polar day, their feeding activity was intermittently continuous around the clock (Fig. 6) (Stokkan et al, 1986). In summer (the only time that was investigated), the activity pattern of the Adélie penguins in Antarctica has since been shown to be similar to that of the Svalbard ptarmigan (Wilson et al, 1989).…”

“…However, all the fat has disappeared by February, when daylight reappears on the islands (Mortensen et al, 1983). Moreover, these changes also happen when captive birds are fed ad libitum throughout the year (Stokkan et al, 1986). The fat reserves are therefore not, as previously thought, used to supplement the daily energy budget during winter, but are instead carefully kept in store for episodes of acute starvation during winter storms (Mortensen and Blix, 1985).…”

“…What about the animals that reside at high latitudes throughout the year? Stokkan and colleagues (Stokkan et al, 1986) studied the resident high Arctic rock ptarmigan at 79°N in Svalbard throughout the year. They found that, like other animals, this bird showed a diel feeding rhythm -feeding primarily in the morning and evening -when there was a difference between day and night during spring and autumn.…”

“…This is supported by experimental evidence that extension of the available subnivean space increases winter survival (Korslund and Steen, Note that the graph has been duplicated to facilitate identification of the feeding rhythms. Reprinted from Stokkan et al (1986).…”

The metabolic cost of incline locomotion in the Svalbard rock ptarmigan (Lagopus muta hyperborea): the effects of incline grade and seasonal fluctuations in body mass

“…In particular, the acquisition of fat reserves in winter means that these birds experience a seasonal doubling of M b , from approximately 500g between March and August to approximately 900g in mid-November. At this time, fat content comprises as much as 32% of M b (Grammeltvedt and Steen, 1978;Mortensen et al, 1983;Stokkan et al, 1986). It has previously been found that Svalbard ptarmigan have adaptations for locomotor efficiency in both summer (Nudds et al, 2011) and winter (Lees et al, 2010), and when young (Lees et al, 2012b); however, it is unknown how the cost of incline locomotion is affected by the dramatic seasonal changes in M b .…”