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eBio
The Effects of Rainfall on Foliage and Ground Arthropod Availability for Kirtland’s Warblers and Other Gleaning Insectivores in the Late Dry Season in The Bahamas
Joseph M. Wunderle Jr.1,*, Patricia K. Lebow2, David N. Ewert3, Jennifer D. White1, and Dave Currie1
1International Institute of Tropical Forestry, USDA Forest Service, Sabana Field Research Station, PO Box 1377, Luquillo, PR 00773, USA. 2Forest Products Lab., USDA Forest Service, Madison, WI 53726, USA. 3American Bird Conservancy, 2310 Science Parkway, Okemos, MI 48864, USA. *Corresponding author.
Caribbean Naturalist, No. 93 (2023)
Abstract
Effects of dry-season rains in the tropics may vary among arthropod taxa with potential consequences for arthropod consumers. To study rainfall effects on availability of different arthropod prey for Setophaga kirtlandii (Kirtland’s Warbler) and other surface-gleaning avian insectivores, we sampled late dry-season (March–April) arthropods over 9 years in an early succession dry forest on Eleuthera, The Bahamas. We sampled arthropods on foliage (with branch clips) and on the ground surface (with 5-min scans) to document variation in biomass and occurrence with prior rainfall for different taxa. We ran mixture models separately for foliage and ground samples with biomass or occurrence of a specified arthropod group as the response variable. Models included the covariates: sample site, year, days after 1 March, and prior cumulative rain amount or number of days with rain in periods of different lengths. Results showed that total biomass of foliage arthropods (predominantly spiders) did not vary with rainfall measures (quantities or prior periods), whereas arthropod occurrence in foliage samples decreased with increases in various rainfall measures reflecting negative response of foliage spiders to rainfall. By contrast, both total biomass and occurence of ground-surface arthropods (predominantly ants and flies) increased in ground samples with rainfall measures, reflecting positive ant biomass responses and positive fly occurrences with rainfall. As the late dry season progressed with days after 1 March, foliage arthropod biomass and occurrence increased with increases in rainfall measures, due to increases in foliage ant biomass and spider occurrences. By contrast, ground arthropod biomass varied little with days after 1 March, but occurrences in ground samples decreased with days after 1 March in models with cumulative rainfall in long-duration periods and with number of rain days in the prior 30 days. Arthropod taxa differed in availability in the late dry season depending on rainfall measure and duration of the prior period with little congruence in rainfall responses between foliage and ground arthropods. These diverse arthropod responses to rainfall are expected to change with increased frequency of heavy downpours and droughts associated with global climate change, resulting in unknown consequences for the Kirtland’s Warbler and other gleaning insectivores.
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