Does flooding influence the types and proportions of prey delivered to nestling Mississippi Kites?

Mississippi Kites (Ictinia mississippiensis) nesting in the Mississippi Alluvial Valley, USA, have consistently exhibited poor reproductive success, reduced average clutch sizes, and evidence of food stress during brood-rearing, raising concerns about population viability. Unlike populations elsewhere, kites nesting in the bottomland forests of this region face dynamic, anthropogenically altered hydrologic conditions that may be affecting the availability of important prey. Therefore, we quantified nestling diets and examined factors thought to be directly influencing the types and proportions of prey delivered to kite nestlings. Specifically, we sought to identify variables affecting the delivery of annual cicadas, the dominant prey item fed to kite chicks in numerous systems, as cicada emergence from subterranean burrows is known to be delayed by flooding. Using time-lapse video, we documented nestling diets and evaluated predictors of diet variability in east-central Arkansas, USA. We found that the delivery of cicadas increased with day of year, and was greatest during the driest of 4 study years. In contrast, the delivery of dragonflies, the numerically dominant prey item, declined with day of year, but increased with water level, and was lowest during the driest year. Although water level was not a strong predictor of the delivery of cicadas, interannual variation in the pattern of cicada deliveries suggests that flooding reduced the availability of this prey item to kites. Also, despite diverse nestling diets, the provisioning of dragonflies and a variety of other arthropods suggests that kites responded functionally to an absence of cicadas. The temporal patterns in prey deliveries that we detected imply that kite nestling diets in bottomland forests of the Mississippi Alluvial Valley may be influenced by water-level impacts on arthropod phenology and abundance.