Effects of food-deprivation on migratory restlessness and diurnal activity in the garden warbler Sylvia borin

Abstract

The present study describes the effects of food-deprivation on migratory restlessness and diurnal activity in the garden warbler, a long-distance migrating passerine. Fourteen first-year birds were held from August through March in individual registration cages and exposed to daylength changes experienced by birds that winter at the equator. With the beginning of the fall migratory season the birds increased their body weights due to fat deposition and showed nocturnal migratory restlessness characteristic for this species. After the birds had deposited more than about 4 g of fat they were food-deprived until their body mass had declined to a value about 1 g above fat free mass. Subsequently they were re-fed. This procedure was repeated through fall and winter, beyond the termination of spontaneous fall migratory restlessness. - Food deprivation consistently caused an increase in duration and intensity of nocturnal activity. After the end of spontaneous migratory restlessness and before the onset of winter molt it led to a reinduction of nocturnal activity. When nocturnal activity increased, the duration of diurnal activity decreased, whereas its intensity increased. With regard to the performance of free-living migrants these results suggest (1) that nocturnal migratory activity is enhanced in birds travelling across areas with unprofitable resting places; (2) that nocturnal migratory activity may be reactivated in birds that have settled for the winter in an area with deteriorating food supply; and (3) that the pattern of diurnal activity may change conspicuously when nocturnal migratory activity is enhanced or resumed.

How far do birds fly during one migratory flight stage?

“…This is supported by capture-recapture data from stopover sites where it was shown that individuals that lost fuel stores departed earlier than individuals that accumulated fuel at medium rates (Schaub et al 2008). In accordance with this, Gwinner et al (1988) showed that migratory restlessness increased when Garden Warblers experienced food deprivation and decreased when given unlimited access to food. Some of the observed shorter movements in this study might be explained by such behaviour.…”

Cryptochrome expression in the eye of migratory birds depends on their migratory status

“…This is a robust and reliable protocol (Biebach, 1985;Gwinner et al, 1985;Gwinner et al, 1988;Fusani and Gwinner, 2004) that provides an alternative and complementary approach to the study of migratory restlessness behaviour in orientation cages such as Emlen funnels (Emlen and Emlen, 1966;Mouritsen et al, 2004). Zugunruhe has been recognized as a strong proxy for migratory status for more than 200 years [Naumann, 1795-1817, cited in Berthold (Berthold, 1988)], and our recent studies in garden warblers have shown that Zugunruhe is an excellent indicator of the actual migratory disposition in Sylvia (Goymann et al, 2010).…”

Allocation of endogenous and dietary protein in the reconstitution of the gastrointestinal tract in migratory blackcaps at stopover sites

“…The blackcaps (N5 males and 14 females) were held in individual cages in an outdoor aviary for approximately 1week. They were provided with a mixture (by mass) of 25% commercial dry insect-based food (Fettmischung fein Aleckwa, Tiernahrung, Altrip, Germany), 30% minced hard-boiled eggs, 21% curd, 15% bread crumbs, 6% ground egg shells, 3% minced beef heart and 0.53% vitamins (Vitakalk and moult vitamins, Södra Vallgrund, Finland) (Gwinner et al, 1988), supplemented with 20-50 mealworms per day per bird. Thereafter, the birds were transferred to a temperature-controlled room kept at 35±0.2°C during the day and 15±0.2°C at night, with constant vapor density, and a light regime following the natural photoperiod (~15h:9h light:dark).…”