Orange-Tufted Sunbirds Do Not Feed Nectar to Their Chicks

Abstract

In most bird species, parents eat the same types of food that they deliver to their nestlings (Ydenberg 1994). Many frugivorous and granivorous species supplement chick diets with arthropod prey that contains essential nutrients such as proteins (Gill 1990), but parents may also eat this food themselves. Several studies have shown that single-prey-loading parents selectively transport large prey to their nestlings and eat smaller prey themselves (Carlson 1985, Krebs and Avery 1985, Sonerud 1989). This may lead to different ranges of prey types being consumed by parents and chicks, but rarely does it lead to exclusive food types for parents versus chicks. Adult Orange-tufted Sunbirds (Nectarinia osea; body mass 6 to 7 g) feed on flower nectar and arthropods, but all observed cases of parental provisioning appear to involve only arthropod prey (Markman et al. 1995, 1996). Therefore, we hypothesized that adult Orange-tufted Sunbirds would feed on flower nectar but would not feed it to their chicks. If so, this would provide us with an experimental tool to manipulate parental self feeding independent of chick feeding and enable us to address questions pertaining to the evolution of parental-care strategies (e.g. Kacelnik and Cuthill 1990, Martins and Wright 1993, Ydenberg 1994). We tested our hypothesis using free-living sunbirds at Sede Boqer in the Negev Desert, Israel, by placing artificial nectar sources in the territories of breeding pairs and using a food dye marker to see whether the young received this nectar from their parents. Methods and results.-In the first experiment, we addressed the question of whether parent sunbirds feed sugar solution to their chicks. We used feeders filled with a 0.25-mol sucrose solution colored red with 0.004 g of food coloring (Maimon Spicesf') per g of water. In a pilot study, we found this to be the highest dye concentration that the parent birds would accept and drink in the same quantities as a clear sugar solution. In order to encourage unbiased use, feeders were covered with brown paper bags, a red artificial flower was stuck in the feeder opening, and a perch was provided in front of each feeder. Each feeder was suspended from a tree 5 m from the nest to enable an observer to watch the nest and the feeder simulta-