Examining breeding bird diets to improve avian conservation efforts
Date
2019
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Improving our understanding of birds' diets is vital to avian conservation efforts. Once we know which arthropod groups are most important to birds and why, we will be better prepared to manage landscapes to facilitate bird conservation by planting the host plants those arthropods need for their survival and reproduction. Four projects were conducted to investigate the arthropod composition of bird diets. Overthree breeding seasons, cameras were stationed at Eastern Bluebird (Sialia sialis) nest boxes in Delaware to record photographs of bluebirds bringing food to their nestlings. Thirty-eight bluebird broods were monitored from hatching until fledging; identification of over 7,000 arthropod prey from photos taken at the nests indicate that the most common prey taxa are Lepidoptera, Orthoptera, and Araneae. Prey choice tests using 24 bluebird pairs were then conducted to assess bluebirds’ insect prey preferences, indicating that waxworm caterpillars are preferred over mealworms, crickets, cabbage looper caterpillars, and stink bugs. Additionally, a community science project was launched to solicit contributions of photos of North American birds eating arthropod prey. Approximately 6,500 photos of bird-arthropod interactions, representing about 320 North American bird species, were contributed by community scientists and the arthropod prey were identified to lowest possible taxonomic level. Having determined which arthropod groups are the best-represented and most preferred in birds' diets, the next step was to identify what makes those groups important to birds. Levels of carotenoids (lutein, zeaxanthin, beta-cryptoxanthin, beta-carotene, and alpha-carotene) were quantified and compared across insect groups. Carotenoids play an important role in boosting the immune system, promoting healthy development, and in determining birds' plumage coloration, important in mate selection. Carotenoid analyses revealed that caterpillars (Lepidoptera) have higher levels of carotenoids than other examined invertebrate groups (Hemiptera, Coleoptera, Hymenoptera: Apocrita, and Araneae). Birds' preferences for certain arthropod groups could be influenced by carotenoid content. The results of this research suggest that managing landscapes in ways that promote theabundance of green, hairless caterpillars (e.g., Geometridae and Noctuidae) should improve resources required by breeding North American birds.