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Bird Conservation in the Hudson River Valley

Hudson Valley Habitat Management Decision Tree (for managing bird habitats): Managing Habitat for Shrub Birds

Field Sparrow © J. Nadler

Background
Shrub habitats are often overlooked when it comes to habitat management and their value underestimated. Old-field and shrub habitats are relatively short-lived, persisting approximately 20 to 25 years, and therefore require periodic management to maintain. Of the 40 bird species associated with shrub habitats in eastern North America, 22 are undergoing significant population declines, and ten of these species are considered at-risk in the Hudson River Valley.

Habitat Description
Different shrub birds are associated with different successional stages of shrub habitat ranging from predominately low herbs and grasses to young forest. In general, shrub habitats have woody plants typically less than ten feet tall with scattered open patches of grasses and forbs. Shrub communities can be dense and impenetrable with numerous woody stems and young trees or can consist of a mosaic of low woody cover interspersed in herbaceous cover. Shrub habitats are common in late stages of old fields, on sandy soils in coastal areas, ridge tops that contain a heavy component of scrub oak, and power line rights-of-way. For most birds, the dominant plant species are less important than the physical structure and hydrologic conditions. The desirable physical components include varying mixes of bare ground, herbaceous cover, woody vegetation of varying heights, and canopy contributing saplings.

Management Recommendations
If you haven’t already, please visit our decision rule tree to determine if managing for shrubs is the best option for your property.

• Maintain adequate patch size
  Shrub habitats between 5-25 acres will provide habitat to a number of the at-risk species; in general, larger is better. However, smaller, isolated patches less than 5 acres can also provide habitat to some of the at-risk species.
• Control woody vegetation
  The mechanism and frequency of management you employ will depend on the current structure and species make up of the area you are interested in managing; tree species require more management compared to shrubs. On average, shrub habitats need to be managed every 5-10 years, sometimes less frequently.
  
  If you have:
  1. Existing shrub habitat without trees (i.e., areas with shrubs interspersed with openings of grasses and forbs), management may be required only every 2-4 years (sometimes less frequently) to prevent the openings from reverting to forest. Management options for maintaining these areas include mechanical mowing, selective removal of trees if they appear, prescribed burning, or grazing.
  2. Existing shrub habitat with trees, trees should be removed by stumping and mowing every one to three years, perhaps coupled with an herbicide application to control trees that may attempt to resprout. The remaining area should be managed as noted above in #1.
  3. An area dominated by trees, shrub habitat can be created by clear cutting and then managing the area every one to three years to remove regenerating late-successional, or shade-tolerant, trees while maintaining the shrub structure. These areas will initially require aggressive management using land clearing equipment such as a hydroaxe, Brown Brontosaurus, tree shear, or hand removal with chainsaws in smaller patches to remove larger unwanted trees, followed by less frequent action (e.g., every three to five years) to maintain the habitat. Once the shrub habitat is established, it can be maintained as noted above in #1.
• Time your management activities so it doesn’t harm birds
  Mowing should not be done during the nesting season (April 15 to August 15) and can take place without serious impacts to wildlife during late fall and winter. However, if trying to control invading tree species, mowing should take place as soon after August 1 as possible, because mowing during the growing season helps to minimize resprouting.
• Control Invasives
  Invasive plants should be removed because many are aggressive and will displace desirable native species if not controlled. For example, autumn olive and multiflora rose can become well established and dominant in two to three years. Mowing and herbicide application are the common management techniques for invasives.

Helpful Resources

Peterjohn, B. June 2006. Conceptual Ecological Model for Management of Breeding Shrubland Birds in the Mid- Atlantic Region. Technical Report NPS/NER/NRR--2006/043. National Park Service. Philadelphia, PA.

Oehler, J. D., D. F. Covell, S. Capel, and B. Long, eds. 2006. Managing grasslands, shrublands, and young forest habitats for wildlife: a guide for the Northeast. New Hampshire Fish and Game Department.

Smith, E. T. 2007. Scrub-shrub Birds. Fish and Wildlife Habitat Management Leaflet Number 42. Natural Resources Conservation Service, Wildlife Habitat Council, Silver Spring, MD.