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Species at Risk: The Least Bittern


The least bittern, listed as threatened under the federal Species at Risk Act, is North America’s smallest heron. It weighs about 80g and measures about 30cm – that’s roughly the size of an American Robin! These little birds breed in Manitoba, Ontario, Quebec, New Brunswick, and possibly Nova Scotia, from late April to early fall, and its range extends as far south as Argentina and Brazil.

Because this bird is very secretive in nature, it’s one of North America’s most poorly known species, and little is known about its migratory routes and winter habitats.

What we do know about least bitterns is that they’re very useful indicator species for the health of marshlands. As a habitat specialist, they prefer to nest in less accessible parts of marshes that contain dense, tall emerging plants like cattails, making them difficult to spot by the untrained eye. To catch their prey (such as small fish, tadpoles, insects), these small herons will sit on a platform constructed out of vegetation, and from their perch, they’ll visually identify prey in the clear shallow water before claiming it as a next meal.

The population of least bitterns in Canada is estimated at 3,000 individuals. Populations have declined by more than 30% in the last 10 years, primarily as a result of loss and degradation of high-quality marsh habitats. Although the rate of decline has since slowed, marshes constantly face the threat of being drained for the purposes of development or for conversion to agricultural uses. Least bitterns are also impacted by any reduction in water quality because they rely on clear waters to find food.

Degradation and loss of marshland habitats have other impacts on the least bittern as well. When marshes are turned into housing subdivisions or farmland, their habitat becomes fragmented, making it easier for predators like raccoons to access the deeper areas, which poses an additional threat to least bitterns. Additionally, because this species migrates at night, any roadways near marshes can be a threat because these birds are at a greater risk of colliding with vehicles, buildings, power lines, fences, and towers.

Careful monitoring of this species is difficult because so little is known about it. As a result of being listed under the Species at Risk Act, a Recovery Strategy was written for the least bittern in 2011. The strategy emphasizes habitat management and conservation measures, and includes requirements for surveying and monitoring the populations closely, along with other critical research. Without this strategy, and indeed without the federal Species at Risk Act, least bittern populations would continue to decline and even disappear, along with the high-quality marshland habitat that they rely on.

Want to help ensure that species like the least bittern continue to benefit from our federal Species at Risk Act? Send a letter now to let the minister know that a strong SARA is important to you!