See my MartinWatch data here
Colony summary by Cavity type for 2015, 2016, 2017, 2018, 2019, 2020
Pay attention to the % of hatchlings that fledge. This is a figure that seems to be pointing to the advantages of the ChirpyNest system.
MartinWatch DATA for 2020 Peaceful Valley Purple Martin Colony
Martinwatch data for 2020 Virginia Highlands Community College Colony
Martinwatch DATA for 2019 Peaceful valley Purple Martin Colony
Martinwatch data for 2019 Virginia Highlands Community College Colony
Nest Check data for 2018 Peaceful Valley Purple Martin Colony
Nest check data 2018 Virginia Highlands Community College colony
25 year martinwatch data summary for my Peaceful Valley Purple Martin colony.