LARGE Bird Roosts:

• Odor, noise, filth
• Droppings deface equipment
• Damage to trees
• Health concerns - Histoplasmosis: The soil in older roosts may harbor fungal spores of this human respiratory disease. Exposure is most likely when dry roost substrate is disturbed.

Prevention and Control:

Vegetation management:

*Street trees: When roosts occur in landscape trees near homes or along streets, thinning side branches from the trees used by birds will usually disperse them. This method was developed from blackbird roost studies in Texas and appears to be an effective approach. Consultation with a professional arborist will help maintain the trees' aesthetic qualities.

*Woodlot or grove of trees: Thin out about one-third of the trees. Generally, such roosts occur in dense, overcrowded stands of young trees; thinning improves tree growth and makes the site unsuitable for roosting. Such thinning successfully dispersed roosts from research woodlots in Ohio and Kentucky, and from at least two problem roost situations in Nebraska. In dense cedar thickets, bulldozing strips through the roost to remove one-third of the habitat has also been successful in dispersing birds. Soil disturbance with heavy equipment, however, may be hazardous if soils harbor fungal spores of histoplasmosis.

*Tree Selection: If planting trees in an area with a history of bird roost problems, avoid trees that have a more closed or dense canopy. For example, fall blackbird/starling roosts appear more likely to occur in trees such as maples, Bradford pear in protected spots, and, to a lesser extent, pin oak. Roosting flocks generally choose dense trees that offer ample perch sites for the large flock and protection from adverse weather. Another point to consider in a landscape plan is that a mix of tree types is less likely to be suitable as a roost site, compared to use of a single species grouping.

*Begin early before birds form a strong attachment to the site. 

*Be persistent until the problem is solved. 

*Dispersing a roost by frightening will likely require 3 or more consecutive evenings to be successful. 

*Frightening devices include recorded distress or alarm calls, gas-operated exploders, battery- operated alarms, pyrotechnics (shellcrackers, bird bombs-contact a professional pest control operator and city ordinances for regulations/permits/restrictions), lights (for roosting sites at night), bright objects, and various other stimuli. Spraying birds with water from a hose or from sprinklers mounted in the roost trees has helped in some situations. Beating on tin sheets or barrels with clubs also scares birds. 

*A combination of several scare techniques used together works better than a single technique used alone. Vary the location, intensity, and types of scare devices to increase their effectiveness.

*Prior to dispersal efforts, consider alerting public officials and neighbors as appropriate about the possible disturbance and about the purpose of the dispersal. Consider also where dispersing birds might go. 

AMERICAN CROW Dispersal:

A tape recorded crow call successfully dispersed crows from individual urban roosts in a recent California study. Crows took flight, circled overhead giving assembly and scolding calls. Crows from nearby roosts flew in and joined. At the end, all crows flew away and left the roosts empty. Study details: The tape was played ~30 seconds on and ~30 seconds off for 4 to 5 times within a 5 minute period. Test 1: 4 roosts; tape played for 3 consecutive nights; roost observed for next 5 nights. Test 2: 1 roost; tape played for 3 nights plus as needed (3 additional nights) to prevent crow return; roost observed for 31 days. Test 3: all roosts in town (20 roosts); tape played for 5 days; roosts observed for 5 more days. Commercially available tape used: "Death Cry of a Crow" (Johnny Stewart, Box 7594, Waco, TX 76710; 817-772-3261). This is the "squalling call" and is also available as "distress call" from Cornell Lab of Ornithology, Library of Natural Sounds, 159 Sapsucker Woods Rd., Ithaca, NY 14850; 607-254-2406). Before such dispersal is attempted, consider where roosting crows might go. updated June 5, 2002

For further information:

Gorenzel, W. P., and T. P. Salmon. 1993. Tape-recorded calls disperse American Crows from urban roosts. Wildl. Soc. Bull. 21:334-338.

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