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Large-scale supplemental feeding alters lay date and nest survival in Eastern Bluebirds but not in two species of chickadees

Cite this dataset

Bailey, Robyn L.; Bonter, David N. (2021). Large-scale supplemental feeding alters lay date and nest survival in Eastern Bluebirds but not in two species of chickadees [Dataset]. Dryad.


Wild bird feeding is a popular and growing activity, with approximately half of households participating in nations including the United States, Canada, the United Kingdom, New Zealand, and Australia. Supplemental feeding can increase survival and reproductive success of birds (which is often a goal of supplemental feeding efforts), but it raises concerns about phenological mismatch, reduced clutch size, or increased risk of nest predation. Our objectives were to test whether access to supplemental food during the breeding season was correlated with (1) advanced egg-laying phenology, (2) increased clutch size, or (3) improved nest survival of 3 cavity-nesting species (Carolina Chickadee, Poecile carolinensis; Black-capped Chickadee, P. atricapillus; and Eastern Bluebird, Sialia sialis) at a large spatial scale (United States and Canada; 22 degrees latitude difference and 55 degrees longitude difference). We examined data from 24,528 nest attempts submitted to NestWatch from 2014–2019. For Eastern Bluebirds, birds with access to supplemental insects initiated clutches 5.83 (± 0.89 SE) days earlier than birds without access to food subsidies, while predicted nest survival was 5% greater for birds with access to supplemental insects (probability of nest success = 0.79, 95% CI = 0.77–0.81) when compared to birds without (0.74, 95% CI = 0.72–0.75). Clutch size of Eastern Bluebirds did not differ between birds with and without access to supplemental insects. For chickadees, supplemental feeding (of seeds, suet, insects, or fruit) was not correlated with phenology, clutch size, or nest survival. Our results suggest that supplemental feeding of insects can be an effective tool for increasing nest survival in Eastern Bluebirds and potentially other food-limited insectivores. However, the efficacy of supplemental feeding for improving reproductive success varies across taxa. Our results can help elucidate how wild bird feeding contributes to global phenomena such as earlier nesting, nest survival, and population change.


Data were collected by NestWatch, a citizen science program operated by the Cornell Lab of Ornithology. Details at and in the Methods section of the manuscript. 

Usage notes

NestWatch data are completely free and open for use. Data summaries are available on the project website: Raw data (the entire NestWatch dataset) are freely available upon request. A complete data dictionary describing all data fields and values is available.