A study of bird deterrent systems performed for the General Services Administration (GSA) by Cooper-Lechy, Architects in 1980 found that neither audio repulsion (distress calls), "scare" systems (plastic owls, rubber snakes), nor poisoning ("baiting") have long term effects on pigeons and starlings in an urban environment. The study also found that tactile systems (sticky gel, porcupine wire, electrified shock) are harmful to masonry as well as ineffective. Numerous other studies confirm these conclusions.

Recent advances in plastic netting and wire anti-roosting systems offer a potentially nondestructive solution for eliminating a variety of nesting and roosting habitats at historic buildings. Anti-roosting wire systems, also known as "pin and wire" and "trip wire", consist of a series of parallel wires of differing height, supported by narrow pins and held under tension by small springs to prevent pigeons from gaining a foothold on ledges. Plastic netting, initially developed for agricultural use, provides a vertical or horizontal barrier to areas where birds seek shelter and build nests. There are many types of netting and a variety of attachment methods. Only a few of these are acceptable for use on historic buildings.

Proposals for installing bird deterrent systems on GSA buildings will be reviewed on a case by case basis by the Regional Historic Preservation Officer (RHPO), in consultation with the State Historic Preservation Officer and Advisory Council on Historic Preservation, as required by Section 106 of the National Historic Preservation Act.

Guidelines for designing and specifying birdproofing systems follow:

Clean First: Clean oil from surfaces prior to installing bird deterrent systems. This removes the corrosive droppings from building materials and permits monitoring the effectiveness of the system. Pigeon droppings are also a health hazard: specify removal using the attached guideline specifications distributed by the Regional Entomologist, Dr. Albert Greene (202) 708-6948.

If possible, coordinate birdproofing with contracts for general exterior cleaning: install systems immediately after cleaning is completed, or in sections as cleaning progresses.

Acceptable cleaning materials are water, dilute detergents specifically formulated for the type of masonry on which they are being used, and poultices specifically formulated for the masonry on which they are being used. All cleaning solutions other than water must be reviewed in writing by the RHPO.

Removing existing systems: Dismantle existing, unapproved deterrent systems before installing new deterrent systems. Use this rule of thumb for dismantling electrified shock systems: if bolt supports can by extracted without damaging masonry, remove bolts and patch holes with mortar matching stone. Otherwise, snap off exposed portion of bolt by striking quickly with a mallet, parallel to edge of architectural element, to avoid breaking stone. Fill void around bolt with sealant. Consult RHPO concerning removal of porcupine wire adhesive or staining caused by sticky repellent.

Anti-Roosting Wire: Use .015 inch diameter clear steel or annealed steel wire. On masonry, support wire with pins driven into mortar joints. On metal (flashed surfaces), mount pins in clear lexan affixed to metal surface with clear silicone sealant. Paint pins to match masonry.

Wire spacing and heights are species-specific. The installer must have an in-depth knowledge of bird behavior and make a site visit to assess the nature of the building's bird problem prior to installation.

Plastic Netting: Use UV resistant, woven, knotted netting only; do not use molded plastic netting. Specify 1/2 to 3/4 inch knot spacing: larger spaces allow sparrow entry. Support netting by pins driven into mortar joints. Tension net with peripheral cabling.

In netting large expanses, use multi-strand polyethylene or polypropylene netting tensioned by springs or turnbuckles. Turnbuckles, where they can be installed inconspicuously, are preferred because they permit adjusting the tension after installation. For small areas, PVC coated monofilament (single strand) netting is acceptable.

For installations close to grade (i.e. within public view) specify netting colored to match adjacent masonry (gray, beige, or dark brown). Well-tensioned black netting is acceptable for upper stories and shadowed areas above the first floor.

Conceal netting edges by conforming to architectural borders (e.g. along curve of arch, from stringcourse to stringcourse, between column capital's necking and abacus. Do not create new lines on the facade. Specify monolithic netting across open expanses to avoid fusible scams. Seamed netting will be permitted only where seams can be aligned with linear architectural elements.

Anchors: Supporting anchors must be smaller in diameter than the masonry joints. Do not penetrate masonry units. Anchors must be removable. Straight-sided pins and screw eyes are acceptable; piton (expanding) anchors are not. Prior to installation, paint pins to match masonry.

Sample installation: Required for each type of system, material, and installation specified. Consult with the RHPO prior to authorizing or approving contractor's samples.

Bidder competency criteria: For netting: "Submit close-up photographs descriptions, and references demonstrating four projects successfully completed within the past five years which are comparable in scale and complexity to work specified in this contract. Deterrence system and nature of installation must be comparable to this project's installation. Photographs must be illustrative.

"For anti-roosting wire: Repeat above, substituting: "Submit ... two projects completed within the past five years".

Guarantee requirement: Minimum five-year guarantee on materials and effectiveness of installation.

Adverse effects: At location where the system will have an adverse physical or visual effect on the building, water washing is the only acceptable solution.

For additional information about bird deterrent systems, call Ms. Caroline Alderson, Assistant Regional Historic Preservation Officer, at 708-6164.

1. All contractor personnel must wear a National Institute for Occupational Safety and Health (NIOSH) approve full face respirator with a high efficiency particulate air (HEPA) filter for screening particles of 0.3 micron size. Dust and particle masks are not appropriate.
2. Respirators must be used in accordance with OSHA regulation, 29 CFR 1910.134 and GSA policy, PBS P 5900.2C, Chapter 3, section 8. This includes fit testing of respirators, maintenance, training, and storage requirements.
3. All contractor personnel must wear protective coveralls, gloves, boots, and hats.
4. Prior to removal, all excrement must be saturated with water under low pressure to prevent debris form becoming airborne.
5. Never use metal scrapers or wire brushes on stone, decorative metal, or other ornamental materials. On historic structures, only nonmetallic tools (such as plastic spatulas and brushes with natural fiber or nylon bristles) must be used to remove the excrement.
6. Removed excrement must be collected in plastic bags, sealed, and disposed of by the contractor at a sanitary landfill.
7. All work must be performed from the outside of the building. Building occupants and the general public must be kept clear of the work site during all operations. It is the contractor's responsibility to provide all barricades, signage, etc. necessary for public protection.