Posted Date: March 22, 2017

Tags: Blog Post  

Himalayan blackberry management by manual control (i.e., cutting or digging) is best conducted when the plants begin to flower as at this stage, the reserve food supply in the roots has been nearly exhausted, and new seeds have not yet been produced. In a typical year, Himalayan blackberry flowers in late spring in the Fraser Valley. As this coincides with the breeding bird season, precautions should be taken to protect nests if large-scale manual control of Himalayan blackberry will be occurring.

The general nesting period for songbirds in this region is from late March – mid-August. By early April, 11-20% of bird species in our region begin nesting; by early May through mid-July, 61-100% of bird species in our region are nesting. Nesting tapers off after mid-July.⁽¹⁾

Bird species that may use Himalayan blackberry for nesting habitat:⁽²⁾

• American robin (nests April through August)
• Anna's hummingbird (nests March through June)
• Rufus hummingbird (nests mid-April through mid-July)
• Song sparrow (nests March through September)
• Spotted towhee (nests April through June)

Bird species that eat berries as a substantial component of their diet:

• American robin (year-round)
• Black-capped chickadee (in winter)
• Black-headed grosbeak (during migration)
• Cedar waxwing (year-round)
• House finch (year-round)
• Northern flicker (in winter)
• Purple finch (year-round)
• Ruby-crowned kinglet (year-round)
• Swainson's thrush (in fall & winter)
• Varied thrush (in fall & winter)
• Warbler species
• Western tanagers (in fall & winter)

Nest Survey Methods⁽³⁾

Prior to large-scale Himalayan blackberry clearing, look for nests or evidence of nesting (i.e., presence of birds in breeding habitat through observation of singing birds, alarm calls, distraction displays) in the area using non-intrusive search methods to prevent disturbance to migratory birds. The following methods can be used to detect nests:

1. Male birds sing to mark the boundaries of their territories. Watch individual males as they move from point to point and sing; these points will outline the approximate territory surrounding a nest site. Within this territory, look for a female calling to her mate.
2. Early in the breeding season nests may be easier to find as vegetation may not have fully thickened, and birds may be carrying nesting materials to the exact nest location.
3. During incubation, if you are near a nest site, birds may fly from the nest. Try to observe where the bird flushed from. Listen for the short call notes and distress cries that birds may give when you are near their nests. Some birds may swoop when you are extremely close to their nests. If distress cries continue for more than a few minutes without finding the nest, do not stay in the area.
4. After eggs hatch, watch for birds carrying food to nests and white fecal sacs away from nests. Be alert to alarm cries of adults and begging calls of young birds that will direct you to nest locations. Be extremely careful not to disturb nestlings that are fully feathered and very alert. They may easily be scared from the safety of their nest before they are ready.
5. Be careful not to disturb active nests.
6. Don't mark the nest location using flagging tape or other similar material as this increases the risk of nest predation. If necessary, flagging tape can be placed at the limits of the buffer zone.

Buffer Zones

When a nest is detected, it should be protected with a buffer zone where vegetation will remain in place until birds have fledged. The setback range for most songbirds and other small birds is 1-5m up to 10-50m or more.1 The recommended setback will depend on the circumstances.

Larger setbacks should be incorporated for activities which cause greater disturbance – such as machine-removal of vegetation, drilling, loud noise, vibration, or regular approach by humans or vehicles.

Birds will develop a tolerance to certain types of disturbance, particularly when they are nesting in developed areas that are subject to frequent minor disturbance (i.e., people and dogs walking by). Birds will also be more tolerant of disturbance when their nest is hidden or in forest/bush habitat (such as Himalayan blackberry). In these instances a buffer zone of a few meters will likely be sufficient to reduce the risk of disturbing a nesting bird.

Two measurements of disturbance distance can be used to determine setback distances⁽¹⁾:

• Alert distance – distance at which the bird adopts an alert posture or emits alarm calls
• Flush distance – distance at which a bird flies away, moves away from a threat, performs distraction displays, or actively defends the nest

The point at which birds exhibit either alert or flushing behaviour is a good indication of their threshold for disturbance, and should be used to determine an appropriate buffer zone or setback distance for Himalayan blackberry removal.

Replacement Species for Himalayan Blackberry

Restoration and replacement of Himalayan blackberry with native, fruit or berry-producing species is important so as to ensure that wildlife habitat is maintained, and to shade out Himalayan blackberry re-growth.

The following species are recommended as they will provide berries and fruits into the winter months for birds⁽²⁾:

• Snowberry
• Salmonberry
• Thimbleberry
• Pacific crabapple
• Black twinberry
• Red elderberry

Information gathered from:

1. Environment and Climate Change Canada, Reducing Risk to Migratory Birds web site: https://www.ec.gc.ca/paom-itmb/default.asp?lang=En&n=8D910CAC-1#_03_1
2. Astley, Caroline. 2012. How Does Himalayan Blackberry (Rubus armenicaus) Impact Breeding Bird Diversity? A Case Study Of The Lower Mainland Of British Columbia
3. Cornell Lab or Ornithology, Nest Watch web site http://nestwatch.org/learn/how-to-nestwatch/how-to-find-nests/