Plants and Animals
Ixobrychus exilis Least bittern
Key Characteristics
Least bitterns are a small secretive marsh bird averaging 11 - 14 inches (28-36cm) in length with a wingspan of 16 - 18 inches (41-46cm). The crown, back, and tail are a vivid greenish black, while the neck, sides, and underparts are streaked with brown and white. Diagnostic characters include chestnut wings with contrasting pale patches and white lines bordering the shoulders. Because of the secretive nature and dense cover used by Least bitterns they are often easier to identify by their low dove-like call. Males give a fast series of 3- 5 "coo" notes, not unlike the Black-billed cuckoo (Coccyzus erythropthalmus). Females have been reported to respond with ticking calls, and the species will utter various cackles and "tut-tut-tut" calls when agitated or alarmed.
Status and Rank
US Status: No Status/Not Listed
State Status: T - Threatened (legally protected)
Global Rank: G4 - Apparently secure
State Rank: S3 - Vulnerable
Occurrences
| County | Number of Occurrences | Year Last Observed |
|---|---|---|
| Arenac | 2 | 2019 |
| Bay | 2 | 2007 |
| Benzie | 1 | 2005 |
| Berrien | 1 | 2014 |
| Cass | 1 | 2009 |
| Chippewa | 3 | 2018 |
| Crawford | 1 | 2024 |
| Delta | 1 | 2022 |
| Grand Traverse | 1 | 2005 |
| Hillsdale | 1 | 2010 |
| Houghton | 1 | 2015 |
| Huron | 1 | 2007 |
| Jackson | 3 | 1995 |
| Manistee | 1 | 2005 |
| Mason | 1 | 2005 |
| Monroe | 2 | 2019 |
| Muskegon | 2 | 2019 |
| Oceana | 1 | 2022 |
| Roscommon | 2 | 1999 |
| Schoolcraft | 1 | 1975 |
| St. Clair | 1 | 2017 |
| Tuscola | 1 | 2007 |
| Washtenaw | 2 | 2006 |
| Wayne | 2 | 2007 |
Information is summarized from MNFI's database of rare species and community occurrences. Data may not reflect true distribution since much of the state has not been thoroughly surveyed.
Habitat
Nests are shallow cups woven of dead cattails, bulrushes, or occasionally twigs and may have nearby vegetation bent overhead giving it the appearance of a handbasket. Nests are placed in tall, dense stands of emergent vegetation over water 4-30 inches deep (10 - 75 cm) and are typically only a few meters from a nearby opening.
Natural Community Types
For each species, lists of natural communities were derived from review of the nearly 6,500 element occurrences in the MNFI database, in addition to herbarium label data for some taxa. In most cases, at least one specimen record exists for each listed natural community. For certain taxa, especially poorly collected or extirpated species of prairie and savanna habitats, natural community lists were derived from inferences from collection sites and habitat preferences in immediately adjacent states (particularly Indiana and Illinois). Natural communities are not listed for those species documented only from altered or ruderal habitats in Michigan, especially for taxa that occur in a variety of habitats outside of the state.
Natural communities are not listed in order of frequency of occurrence, but are rather derived from the full set of natural communities, organized by Ecological Group. In many cases, the general habitat descriptions should provide greater clarity and direction to the surveyor. In future versions of the Rare Species Explorer, we hope to incorporate natural community fidelity ranks for each taxon.
Management Recommendations
The protection, management, and improvement of large shallow wetlands with robust growth of emergent vegetation is perhaps the most urgent conservation need of this species. Several authors have indicated that marshes with a 50:50 ratio of open water to emergent vegetation, often termed hemi-marshes, attract the highest densities and diversities of wetland birds. Managing wetlands for the hemi-marsh stage would improve conditions for Least bittern and other wetland birds. Wetlands should also be protected from chemical contamination, siltation, eutrophication, and other forms of pollution. Best management practices, such as filter strips, no-till farming, and conservation tillage, are valuable tools in protecting wetlands from pollution. Initiatives that encourage wetland restoration and protection on private and public lands have been effective at conserving habitat for this and other wetland-dependent birds. Federal programs funded by the Farm Bill, such as the Wetlands Reserve Program and Conservation Reserve Program, and the North American Wetlands Conservation Act are good examples of efforts that have had positive benefits for an array of wetland species. Changes in water quality could adversely affect the Least Bittern's prey base and increase the potential impacts from a nematode parasite (Eustrongilides spp.), which can devastate wading bird populations.
Active Period
Migration from third week of April to second week of May
Migration from first week of September to fourth week of October
Nesting from second week of May to first week of August
Survey Methods
Surveys are most successful when conducted during the early breeding season prior to incubation. As with many secretive marsh bird species, broadcasting conspecific calls can increase the effectiveness of surveys dramatically. Several surveys may be necessary to determine if Least bitterns are present because they do not call as frequently or as loudly as other birds. The breeding status, however, is best confirmed by searching emergent vegetation for nests and young between mid-June and late July. Least bitterns can be heard during the early morning and evening hours, however, responsiveness to call-response surveys may be higher in the morning and they are usually silent during midday and afternoon.
Broadcast conspecific call
Survey Period: From third week of May to fourth week of June
Time of Day: Morning (sunrise)
References
Survey References
- Bibby, C.J., N.D. Burgess, and D.A. Hill. 1992. Bird Census Techniques. Academic Press, New York.
Technical References
- Evers, D.C. 1994. Endangered and Threatened Wildlife of Michigan. The University of Michigan Press, Ann Arbor. 412pp.
- Monfils, M.J. 2003. Special Animal Abstract for Ixobrychus exilis (Least bittern). Michigan Natural Features Inventory, Lansing, MI. 6pp.