Nutrient Utilization of Winter Retained and Spring Ripened Fruit by Cedar Waxwings (Bombycilla cedrorum)

Abstract

Frugivores that winter-over in temperate climates must use strategies that exploit any remaining fruit sources in order to obtain nutrients until spring fruit develops. This study compares nutrients available in persistent, winter retained fruits to nutrients available in late spring ripened fruits and utilization of those fruits by cedar waxwings (Bombycilla cedrorum). Uneaten fruit samples from Washington hawthorn (Crataegus phaeropyrum), crabapple (Malus sp.), serviceberry (Amelanchier canadensis), and Japanese scholar tree (Sophora japonica) sources along with corresponding resultant fecal waste samples were analyzed for dry mass content of Na+, K+, Mg2+, Ca2+ and N. Waxwing intakes of each nutrient were also compared with known requirements for growing eastern bluebirds. Findings suggest that waxwings are in positive balance for K+, Mg2+, and Ca2+ for the tested winter and spring fruits and that three of the four tested fruits may be adequate in maintaining a nitrogen budget. Winter retained hawthorn fruit may not be an adequate source of Na+. All other nutrients tested in both winter retained fruit diets showed positive balance for wild waxwings. Nutrient levels in over-wintered hawthorn fruit were found to change over time to provide a more optimal nutrient source. Some tested nutrient levels consumed by waxwings fell below levels required by growing bluebirds.