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Biology Program

Environment A-Z


Wildlife on Bridges - Questions & Answers


WSDOT’s bridges are home to many species of wildlife

Pigeon Guillemot on bridge pier.
Pigeon Guillemots on a bridge pier.
Bridge structures, sign bridges and highway light poles provide nesting areas for many species of wildlife, including a number of protected birds. Most of these species are protected by state or federal laws, which can make it challenging for the Washington State Department of Transportation (WSDOT) to carry out needed maintenance and construction activities on and around these structures.


 What species are most commonly found on bridges?

WSDOT biologists have identified 29 different species that use our bridges for part of the year. Some of the species most commonly found on WSDOT bridges include:

  • Bats
  • Cormorants – Brandt’s, double-crested, pelagic
  • Gull – western, glaucous-winged
  • Osprey
  • Barn owls
  • Peregrine falcons
  • Pigeon guillemots
  • Rock doves 
  • Swallows – barn, cliff, violet green

 How are bridges important as bird habitat?

Some species just use the bridges for roosting or perching, others use them for nesting.

Peregrine falcons, which use bridges for nesting, roosting and foraging, were recovered from the brink of extinction in part through the establishment of populations in urban areas.

Other species like the barn owls are suffering from a shortage of natural nest sites and are finding our bridges suitable as nesting areas. Still others, like the pelagic cormorant, have begun nesting on WSDOT bridges, as biologists believe, in order to keep their young safe from bald eagles, which are predators in the cormorant's natural nesting colony sites. One of the state's bridges is supporting the largest pelagic cormorant colony in the state.



 What activities does WSDOT conduct on bridges?

WSDOT uses a special
WSDOT uses a special "under bridge inspection" truck to conduct routine bridge inspections.
Most activities on WSDOT bridges are done to inspect, maintain and preserve the useful life of the structure, such as:

  • Routine bridge inspections – both above and below the driving surface
  • Washing and cleaning, including sand-blasting
  • Painting steel components
  • Repairing deck, structure, expansion joints, mechanical elements
  • Replacing navigational lights



 How does WSDOT avoid impacting birds nesting on bridges?

WSDOT installs bird netting on bridges
WSDOT installs bird netting on bridges in advance of projects that would otherwise disturb birds during nesting periods.
There are a number of ways WSDOT can perform its work and avoid impacting nesting birds. In some cases, we may take preventative measures to keep birds from building nests on bridges when we have planned work on the bridge that coincides with the nesting season. Other methods include:

  • Scheduling work outside of nesting season. Nesting periods for protected birds vary from species to species, starting as early as February for the peregrine falcon to ending as late as mid-October for pelagic cormorants. If work cannot be scheduled outside of the general nesting period for that species, we try to determine the schedule for that pair of birds, and schedule our work outside of the incubation and fledgling period.

  • We may conduct our work away from nests that contain eggs or young. For instance, we may work on top of the bridge, well away from birds nesting underneath the bridge.

  • Providing alternative nest sites by relocating the nest prior to nesting season.

  • Preventing the birds from building nests by hanging bird netting or placing blocks in areas where they would build their nests.



 What happens when our efforts to discourage birds from nesting fail?

WSDOT crews remove osprey nest
Crews carefully remove an osprey nest from a bridge in southwest Washington. It will be relocated nearby.
WSDOT makes every effort to take nesting birds into consideration when scheduling construction and maintenance work.

In a few instances, when our preventive measures failed to discourage birds from nesting, and the project schedule did not allow avoidance of the nesting season, WSDOT has obtained permits from the US Fish and Wildlife Service and Washington Fish and Wildlife Department to remove the eggs or young and have them reared and released by a licensed rehabilitation facility.



Contact:  Marion Carey, Fish and Wildlife program manager, WSDOT Environmental Services, 360-705-7404,