Great Blue Heron
| Scientific Name | Ardea herodias |
| Survival Strategy | Short-distant / Medium-distant Migrant |
| Arrival in Upper Midwest | Late March to early April |
| Depart | Mid-September to late October |
| Destination | Southern United States, Central America, and Northern South America. |
| Conservation Dtatus | Least Concern |
Spring
Great blue herons return to their rookeries in late March to early April. They lay 2 to 4 eggs from late April to early May, with incubation lasting approximately 27 days.
Summer
In July, most Parents brood their hatchlings which last about three to four weeks, and young birds take their first flight around seven to eight weeks, typically in mid-August.
Fall
Migration begins in September through late October for northern populations of great blue herons, with some individuals waiting until well into November when ice makes finding food difficult. Herons from warmer regions are less likely to migrate.
Winter
Non-migrant herons with access to even the tiniest spot of open water will “ice fish” motionlessly, waiting for their next meal. Herons that migrated to warmer regions will have less difficulty feeding in their ice-free summer range.
Behavior
Fueling Migration
Observations by wildlife biologists suggest that Great blue herons add additional fat in the late summer to fuel their southward migration, which can cover more than 1000 miles. Researchers used a GPS transmitter to track a female great blue heron named Harper. She flew non-stop for more than 38 hours over the Atlantic from New Brunswick, Canada, to Nocatee, Florida.
Safety in Numbers
Great blue herons raise their young in treetop rookeries to avoid predation. A larger group of birds has more eyes watching for predators.
Physiology
Cold feet, Warm bird
Standing in cold water while patiently hunting for a meal would quickly chill a human, but this is no problem for a great blue heron. Like other birds, herons use countercurrent heat exchange to conserve heat they would otherwise lose through their bare legs. The veins and arteries in the bird’s featherless legs are close to each other. Before the warm arterial blood gets to the heron’s feet, the veins absorb much of the heat and return it to the body. This exchange of heat keeps a bird’s feet colder, often just above freezing. Birds have little muscle or nerve tissue in their exposed legs and feet, so there is no need to waste energy keeping them warm.
Cooling Down
To lose excess heat in the summer, herons use “gular flutter.” By rapidly flapping the gular skin in their throat (think pelican pouch), they create a radiator that transfers heat from their blood vessels to the outside air.
Diet
Great blue herons are carnivores that eat almost any animal found near the edge of rivers, lakes, or marshes that is small enough to swallow. Their diet is mainly fish and includes frogs, snakes, young birds, small mammals, crayfish, and dragonflies.
Lifespan and Mortality
The average lifespan of a great blue heron is 15 years, with some individuals reaching 30 or more years.
The first year of a great blue heron’s life is the toughest, with mortality estimated to be 69%. The likelihood of not surviving the second year drops to 36%. Mortality for adults three years or older is 22%.
Extreme cold
Herons of the upper Midwest that delay migration into mid-November risk periods of extreme cold, locking their food supply under a layer of ice. If snow cover prevents hunting small mammals, starvation is likely.
Predators
Bald Eagles are the dominant predator of great blue herons, and they prey on heron eggs, nestlings, juveniles, and adults. Other predators include raccoons, bears, turkey vultures, and red-tailed hawks.
Climate Vulnerability
The range of the great blue heron will likely remain stable in a warmer climate. Spring heatwaves may impact nesting success, and repeated wildfires may diminish habitat quality.
Never stop learning
First Nations: the Ojibwe word for heron is “zhashagi.”
Paleontology: fossil records of herons date back 38 to 60 million years.
References
| Naumann, R. 2011. “Ardea herodias” (On-line), Animal Diversity Web. Accessed November 08, 2021 at https://animaldiversity.org/accounts/Ardea_herodias/ |
| Vennesland, R. G. and R. W. Butler (2020). Great Blue Heron (Ardea herodias), version 1.0. In Birds of the World (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.grbher3.01 |
| How Climate Change Will Reshape the Range of the Great Blue Heron https://www.audubon.org/field-guide/bird/great-blue-heron |
| Great Blue Heron – Wisconsin Breeding Bird Atlas https://ebird.org/atlaswi/species/grbher3/US-WI |
| Great Blue Heron – Species Map – eBird https://ebird.org/map/grbher3 |
| Heron Observation Network of Maine https://www.facebook.com/maineheron |
| The Ojibwe People’s Dictionary: zhashagi (na) https://ojibwe.lib.umn.edu/main-entry/zhashagi-na |