The great blue heron (Ardea herodias) is one of America’s largest and most recognizable birds. They can be found patiently stalking their prey near shallow water environments pretty much all over the United States. One fascinating side of their biology is their lifespan and the factors that affect their longevity.
Great Blue Herons have been known to live as long as 24.5 years, but the average is far less. In fact, about 70 percent of great blue herons will perish within their first year after hatching. If they can make it to adulthood, they are likely to live about 5 years on average.
There are many factors that affect how long an individual is likely to survive. This article delves into this subject and discusses the life (and death) of one of America’s most impressive waterbirds.
Although great blue herons are capable of living long lives, their average lifespan is around 5 years
Birds are not the easiest animals to study when it comes to longevity. They are usually highly mobile, show little variation between other members of their species, and change little in appearance once they have their adult plumage.
Researchers typically band juveniles and then rely on recovering these bands from deceased birds to determine their age at death. In this way, scientists have determined that the maximum age of great blue herons is over two decades, although the vast majority of birds do not survive to adulthood. A study in Canada found the average age of breeding adults to be about five and a half years.
The oldest wild great blue heron was 24.5 years old. Very few of these large shorebirds will get anywhere near that age, however. Mortality is very high, particularly within the first two years of their life.
A study done on Great Blue Herons between 1916 and 1958 showed that 71% of the sample (349 birds) died within their first year after hatching. These results are very similar to a 1972 study that found a mortality rate of 69% in the first year. They also compare very closely to the findings of a similar study done on another large species, the gray heron.
The studies found that mortality rates decreased dramatically if the birds survived their first few years. In fact, the estimated life expectancy of birds that survived their second year was a further three years or so. Since great blue herons reach sexual maturity at an age of 22 months, it is fair to say that the average individual that reaches maturity has a total life expectancy of about five years.
A great blue heron near Hauser Lake, Idaho
Generally speaking, captive birds are far easier to study. If you think about it, most birds in captivity receive good health care, regular meals, shelter from extreme weather conditions, and a large degree of protection from predators.
Unfortunately, great blue herons generally don’t adjust well to life in captivity because they are easily stressed and difficult to feed. Nevertheless, one Californian zoo claims to have kept a non-releasable captive specimen for no less than 18 years.
Early 20th-century banding studies found that about 24% of recorded mortalities were from gunshots. While this certainly still happens, one can only hope the modern picture has changed! Sadly, many waterbirds like great blue herons also die after becoming entangled in fishing lines, nets, and other trash.
Read on to learn more about the various causes of great blue heron mortality.
Great blue herons can be host to a number of different parasites including Giardia, flatworms, and nematodes that can affect their health. They can also be susceptible to viruses like avian poxvirus.
Industrial chemicals and heavy metals like mercury have been responsible for mortality and reduced breeding success. Improved environmental regulation has apparently reduced the threat in many areas but it remains a concern.
Great Blue Heron eating a fish on the beach
A variety of predators feed on great blue heron eggs, chicks, and even adults. Predators include birds of prey, carnivorous mammals, and even large reptiles. Predators are likely to be responsible for the deaths of many great blue herons that are injured, exhausted, or in distress.
There are several records of great blue herons biting off a little more than they can chew! These hungry (and unfortunate) birds have died after attempting to swallow large fish including pacific lampreys and carp. They can also choke on other large prey items like frogs and snakes.
Severe storms and hurricanes can certainly be responsible for high mortality rates. In northern areas, unusually cold conditions can also result in water bodies freezing over which can make many of their usual prey items impossible to catch.
Great blue herons breed in the spring. The male collects most of the nesting material but it is the female who builds the nest. Construction can take many days, and the same nest can be used year after year, growing in size each time it is used.
Great blue herons lay two to six eggs and these are incubated for about a month. The chicks are helpless at first and spend up to 81 days as nestlings. The young birds reach sexual maturity and begin nesting for the first time at about 22 months old.
Blue Heron chick in the nest
Great blue heron eggs and chicks may be eaten by a diverse array of predators including ravens, crows, and golden and bald eagles. In fact, bald eagles have even been known to prey on adult great blue herons. Recorded mammalian predators include bears and raccoons.
In the south, American alligators and introduced Burmese pythons are also a threat, although the tables can be turned and herons are known to feed on hatchling alligators.
The oldest recorded great blue heron was 24.5 years old when it was found in Texas. It is probably reasonable to expect that older birds do, or have existed, however.
Great Blue Heron flying above the water
Healthy great blue herons can probably survive for several days without a meal.
The exact length of time would definitely depend on various factors like the individual's health, body fat levels, and environmental conditions like temperature. No clear data is available, and we can only hope no one plans on conducting such a study!
Great blue herons are hardy birds, but they are also able to survive winter by migrating south to warmer areas. Not all great blue heron populations are migratory, however. These birds are able to remain year-round in areas with water bodies that do not freeze over.
Populations on the Pacific Northwest coast do not migrate at all, but most of the birds that spend summers in the far north will begin a southward migration in the fall months of September and October. Many of these birds will spend the winter in much warmer regions like the Caribbean and Central America.
Close up of a great blue heron with a recently caught fish
Great blue herons are a widespread and common species. They are ranked as ‘Least Concern’ by the International Union for Conservation of Nature (IUCN). Their populations appear to be fairly stable, with some increases in the United States and decreases in Canada.
Fortunately, these magnificent birds do enjoy protection under the Migratory Bird Treaty Act. This means it is illegal to kill or harm great blue herons in any way in the United States.
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