Phenological Mismatch in Breeding Cerulean Warbler (Setophaga cerulea) and Prey Variability Among Tree Species in Male Territories

Brittany K. Nahorney¹ and Kamal Islam^1,*

¹Department of Biology, Ball State University, Muncie, IN 47306. *Corresponding author.

Northeastern Naturalist, Volume 32, Issue 4 (2025): 542–561

First published early online: 27 December 2025

Abstract
Arrival of avian species to breeding grounds is often synchronized with peak food availability, particularly caterpillars, which are essential to many passerine nestlings. As climate change advances breeding ground daily mean temperatures and initiates earlier spring caterpillar hatching, long-distance migrants may be at risk of missing peaks in caterpillar abundance if they are unable to adjust the timing of reproduction. It is unknown whether timing of the nestling stage coincides with peak larval Lepidoptera abundance in Setophaga cerulea (Cerulean Warbler), a declining insectivorous, Neotropical–Nearctic migrant. The objectives of this study were to determine if peak nestling resource demand of Cerulean Warblers is synchronized with caterpillar abundance and identify differences in caterpillar frass fall among tree species in south-central Indiana. Mean hatch dates and greatest nestling resource demand occurred after peak caterpillar abundance, and timing of nest stages and greatest food availability occurred earlier in 2023 compared to 2022. Carya ovata (Shagbark Hickory) dropped significantly greater frass fall than other tree species, and mean frass fall differed between years for most tree species. Spring temperatures are expected to continue occurring earlier, and these results illustrate the importance of monitoring possible mismatches between breeding dates of long-distance migrants and peak periods of Lepidoptera larvae to determine if asynchrony may affect nestling growth and fledging success. Additionally, knowledge of tree species in Cerulean Warbler territories that support greater numbers of caterpillars may be used to manage breeding habitat for tree species, such as Shagbark Hickory, that have an abundance of larval Lepidoptera.

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