Improving our understanding of birds' diets is vital to avian conservation efforts. Once we know what makes certain arthropod groups more desirable to birds, we will be better prepared to manage landscapes to facilitate bird conservation by encouraging the inclusion of the host plants those arthropods need for their survival and reproduction. A citizen science project was launched to solicit contributions of photos of North American birds eating arthropod prey. Additionally, over three breeding seasons, cameras were stationed at Eastern Bluebird nest boxes in Delaware to record photos of the bluebirds bringing food to their nestlings. The birds’ prey was identified from the photographs and quantified to assess which groups are the most important in the birds’ diet. Prey choice tests were then conducted to assess bluebirds’ insect prey preferences. 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. 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.
Results/Conclusions
Approximately four thousand photos of bird-arthropod interactions, representing about 250 North American bird species, were contributed by citizen scientists and the arthropod prey were identified to lowest taxonomic level. These identifications indicate that caterpillars (Lepidoptera) are the most important food group for North American breeding birds. Thirty-eight Eastern Bluebird broods were monitored from hatching until fledging; identification of insect prey from photos taken at the nests indicate that most common prey groups include caterpillars, spiders (Araneae), and orthopterans. Prey choice tests demonstrated that caterpillars (cabbage loopers, waxworms) are preferred over mealworms (Coleoptera) and crickets (Orthoptera). Carotenoid analyses revealed that caterpillars and sawfly larvae (Symphyta) have substantially higher levels of carotenoids than other examined arthropod groups (Diptera, Orthoptera, Hemiptera, Araneae, Coleoptera, Opiliones, Dermaptera, and Apocrita). Birds' preferences for certain arthropod groups could be influenced by carotenoid content.