Least Bittern

(Ixobrychus exilis)

Status: Threatened (ESA 2008 & SARA 2003)

Table of Contents:

Species Identification
Diet
Habitat and Range
Biology and Behaviour
Similar Species
Threats/Reasons for Being Endangered
Conservation and Recovery Strategies
How You Can Help

Species Identification:

This tiny heron keeps well-hidden amongst cattails and bushes. At about 30 cm tall, they are the smallest heron in the western hemisphere. The Least Bittern is light brown along their sides with a white throat and belly, and darker feathers on their back. They have a large, long yellow bill and yellow legs. The male’s head and back are much darker than the female and juvenile, and they are more frequently heard than seen. Their common call is a gentle, “coo, coo, coo,” and when alarmed they give a rapid, “rik-rik-rik-rik”.

Diet:

The Least Bittern primarily eats small fish by stabbing them with their long bill. They also eat leeches, small mammals, frogs, crayfish, small snakes, and large insects. They will often build platforms in shallow water to hunt off of. They hunt by standing patiently by the water, and may even hang off vegetation to reach down into the water, or quietly stalk their prey.

Map taken from Cornell Lab: https://www.allaboutbirds.org/guide/Least_Bittern/maps-range

Habitat and Range:

The Least Bittern’s breeding range extends across southeastern Canada and most of the eastern United States. They are found in southern parts of Manitoba, Ontario, Quebec, New Brunswick and a bit of Nova Scotia. Ontario has the highest concentration of Canadian breeding population, especially in southern Ontario. Populations in Ontario are concentrated in the southern half of The Land Between, and at the southwestern tip of the province near Lake St. Clair. Population trends and range boundaries are hard to confirm because the species is so secretive and difficult to survey.

Least Bitterns overwinter along the Gulf Coast in Texas, Florida, and in Baja California, and into the coastal lowlands of Mexico and Central America. Separate populations of Least Bittern are year-round residents within coastal pockets of South America. It is often difficult to distinguish between overwintering and year-round residents in the Central American range.

They breed in freshwater wetlands with lots of emergent vegetation, which are most commonly found in large cattail-dominated marshes with shallow water and patches of open water (known as a “hemi-marsh”). They use vegetation for building nest platforms, hunting platforms, and as a protection against predators. Marshes greater than 5 hectares are more likely to be used by Least Bitterns, especially those within a broader landscape mosaic of wetlands. Water also needs to be clear enough so they can see their prey.

Biology and Behaviour:

Adults arrive back to their nesting sites starting in late April. Male displaying behaviour takes place for about six weeks starting early May. This is the best time to hear their calls and to detect them using call playbacks. Amongst dense vegetation, the male will build a nest platform by piling dry plant stalks onto bent marsh vegetation. 4-5 eggs are laid on average and incubated for up to 20 days. After about a month of being fed by their parents, the young transition into hunting for themselves, and then disperse in late summer. The fall migration starts in late August to late September.

Adults are preyed on by snapping turtles and raptors. The young are also vulnerable to snakes, raccoons, minks, corvids, and other herons. The Least Bittern has low tolerance to habitat changes, making them susceptible to illness and diseases. They also have low tolerance for fluctuating water levels.

Similar Species:

American Bittern is similar to the Least Bittern, but they are larger and less colourful
The Black-crowned Night-heron and the Yellow-crowned Night-heron juveniles differ from the Least Bittern since they have dark brown underparts

Threats/ Reasons for being at Risk:

1. Habitat loss and degradation in breeding grounds: This is the main threat to Least Bittern populations. Historically, wetlands in Ontario and Quebec were drained, dammed, and channelized for agriculture and settlements. Today, watersheds in the Great Lakes region are still being altered for urban expansion, agricultural development, and cottage development. These changes contribute to sedimentation, eutrophication, and water level fluctuations in the wetlands that Least Bitterns rely on.

2. Toxins and disease: Wetlands tend to accumulate toxins that runoff from the surrounding landscape- especially agriculture. Biotoxins accumulate in predators, and wildlife like herons are particularly vulnerable to bioaccumulation since they are higher up in the food chain. DDE and dieldrin have been found in herons in Ontario and are linked to eggshell thinning. High levels of mercury and PCBs have also been found in the Great Lakes region.

3. Invasive species: Invasive species like Purple Loosestrife, Reed Canary Grass, and Phragmites are outcompeting native cattails and altering wetland vegetation. These species will create monocultures of plant matter that wildlife cannot use as a food or nesting source, making once natural wetlands no longer habitable.

5. Collisions and recreational activities: While this has been more readily reported in southern areas of their range, accidental collisions remain a likely threat in Ontario. This includes collisions with cars, boats and generator towers. Recreational boating may also disturb herons during nesting season.

Conservation and recovery strategies:

The Provincial and Federal recovery strategies have so far focused on filling in information gaps on the Least Bittern through monitoring and research projects. Survey protocols have been established for their breeding season. So far 54 critical habitat sites have been identified in Ontario, but more habitat analysis needs to happen. In Ontario, Species at Risk at the Threatened level have all habitats automatically protected.

How can you help?

Control invasive species on your property, and volunteer to help pull invasive species in your community- especially Phragmites.
Adhere to speed restrictions when boating, and be cautious when traveling near wetlands.
Ensure your municipality follows existing legislation like the Wetland Protection Act and the Endangered Species Act.
Help wetlands on your property by leaving wide riparian buffers, orienting lights away from water, and keeping pets away from wetlands.
Support local farms that follow sustainable practices and limit the use of pesticides.
Join local conservation organizations and birding groups, and report any sightings of rare species like the Least Bittern to the Natural Heritage Information Centre and to applications like eBird or iNaturalist.

Additional Resources:

Cornell Lab of Ornithology page
Georgian Bay Biosphere reserve page
COSEWIC 2009 Assessment and Status Report

Sources:

COSEWIC. 2009. COSEWIC assessment and update status report on the Least Bittern Ixobrychus exilisin Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 36 pp. (www.sararegistry.gc.ca/status/status_e.cfm).

Ontario Ministry of Natural Resources and Forestry. 2016. Recovery Strategy for theLeast Bittern (Ixobrychus exilis) in Ontario. Ontario Recovery Strategy Series. Prepared by the Ontario Ministry of Natural Resources and Forestry, Peterborough, Ontario. v + 5 pp. + Appendix.