Seasonal changes in water and fat content and fatty acid composition of the catkin buds of Alaska willow (Salix alaxensis).

Catkin buds of Salix alaxensis from interior Alaska were analyzed for water and lipid content and fatty acid composition throughout the year. Water content was significantly correlated with environmental temperature, but lipid content was not. Linoleic acid (18:2) and arachidic acid (20:0) were predominant in the lipids of whole catkins.Of the 27 different fatty acids found in all weekly samples, 11 showed pronounced seasonal variation, most of which occurred during catkin development and flowering in spring. During winter, only the amount of linoleic acid in the catkins was significantly negatively correlated with change in ambient temperature.Histological and chemical analyses of the catkin florets and catkin scales revealed that 99% of the linoleic acid was located in the florets primarily in the form of triglycerides while 94% of the arachidic acid was located in the catkin scale primarily as wax esters. While the linoleic acid in the triglycerides of the meristematic florets probably provides an energy source for the developing catkins, the large amounts of arachidic acid located in the catkin scales probably serves to prevent dessication of the catkins during the long, cold and dry arctic winters.

The annual lipid cycle and feeding behavior of Alaskan redpolls.

Total lipids were extracted from 161 redpolls (Acanthis spp.) collected each month of the year from October 1962 to September 1963, in interior Alaska. A lipid index (Weight of ether extract x100/live body weight) was calculated for each sample. Lipids were also extracted from sections of pectoral muscle, livers and hearts representing each month.Body weight and lipid index were significantly positively correlated being highest in January and lowest in September. Total lipid content was significantly inversely correlated with air temperature; the high autumn and spring pre-migratory lipid peaks of migratory species were only weakly expressed in the redpolls. Liver lipid showed a significant annual variation being highest in December and lowest in August, while lipid from heart and pectoral muscle did not vary seasonally.Five birds were held in captivity during spring and summer at a constant temperature of 22°C. Food consumption was 5.1 g/day or 22.4 kcal. The caloric value of the most extensively utilized natural food, birch seed (Betula papyrifera), was determined (5.4-5.5 kcal/g dry wt). When esophageal diverticulae are full (2.0 g wet wt) of birch seeds, the resulting energy yield may sustain an individual for only a fraction of a 24 h winter day in contrast to other arctic herbivores (e.g. ptarmigan, Lagopus sp.) in which a full crop may suffice for the full 24 h period.

Latitudinal and population specific differences in timing of daily and seasonal functions in redpolls (Acanthis flammea).

1. The daily (circadian) rhythm of activity and rest of common redpolls (Acanthis f. flammea L.) from 65°N lat. was measured for about one year in individuals outdoors at two latitudes (48° and 65°N). During winter at both latitudes, activity-time (α) of common redpolls approximated the duration of daylight (including civil twilights); onset of activity, however, occurred at lower light intensities than end of activity. During mid-summer, a rest-time (p) of ca. 5 h was maintained at both latitudes. During the times of spring and fall migration (extending into summer or winter, respectively), common redpolls showed nightly unrest or shifted their onset of daily activity into the pre-dawn hours. 2. Redpolls of two subspecies (A. f. flammea and A. f. cabaret Müller) resident at different latitudes (ca. 65° and 49°N) were maintained and measured under the same light conditions at 48°N lat. The two populations showed significant differences in their responses to the same annual changes in day length which included: (i) differences in the timing of the circadian activity rhythm with respect to the daily solar cycle; (ii) differences in the amount and range of seasonal changes in nightly unrest; (iii) differences in the mean level and range of seasonal changes of body weight; and (iv) differences in the timing of postnuptial molt. 3. In all experimental groups of redpolls, the highest "precision" (i.e. lowest mean day-to-day variation) in onset and end of activity was observed when both phases occurred during the twilights. The different effects of annually changing light conditions on onset and end of activity with respect to solar time indicated that timing of these two phases of the activity rhythm is independently controlled. It is further indicated that an annually changing sensitivity to light controls the termination of activity in common redpolls, although ambient temperature can modify this response. 4. Besides the direct influence of latitude on timing and the amount of changes of various circadian and annual functions throughout the year, the important role of long-term (genetic?) adaptation to the light and temperature conditions prevailing in the respective habitats of redpoll populations is emphasized by the results of this study.