Ecological survey reveals substantial population growth alongside colony fragmentation in great blue herons, suggesting behavioral adaptation to bald eagle recovery.
Key Points
To assess the population status, breeding distribution, and colony size dynamics of great blue herons relative to historic benchmarks.
Surveyed great blue heron colonies across the tidal reach of the Chesapeake Bay in 2013.
Compared colony abundance, breeding pair estimates, and nesting habitats with benchmark surveys from 1975–1976, 1985, 1993, and 2003.
Heron breeding colonies grew from 37 (3,680 pairs) in 1975–1976 to 423 (15,094 pairs) in 2013, with doubling times of 10.8 years for colonies and 18.8 years for pairs.
Colony size decreased across the multi-decade period (β = −0.032 ± 0.004, P < 0.001) at an annual rate of −3.2%, with colonies holding >100 pairs falling from 34% in 1985 to <4% in 2013.
Large colony abandonment and fragmentation coincided with bald eagle recovery, leaving 60% of colonies representing <0.1% of the regional population.