Tree Care and Maintenance

Seasonal Tree Care Tips: Winter 2022
Nesting Season

Birds nest in a wide variety of places including tree branches, cavities, logs and stumps, on the ground, under shrubs, in open gravel, along stream banks, in chimneys, on bridges, ledges and light poles, and under the eaves of your house. Activities that threaten nesting birds are not limited to tree removal and pruning; mowing your lawn, clearing invasive or native vegetation from the ground, grading and building, or applying herbicides are all potentially disruptive.

The Migratory Bird Treaty Act (MBTA) of 1918 provides protection to all native bird species, even native species that are non-migratory. There are over 200 native bird species in the Portland area, including common species like robins and song sparrows, and less common species like flycatchers and bushtits. This Federal law, administered by the United States Fish and Wildlife Service (USFWS), makes it illegal to hunt, pursue, wound, kill, possess, or transport any native bird, their eggs, feathers, or nests, either intentionally or accidentally, without a permit from USFWS.

Nests are only protected when they are active, meaning when they contain eggs or young. Once fledglings have left the nest, the nest is no longer protected by law. In general, nesting season in our region is divided into three timeframes:

  • August 1 – January 31 is the non-breeding season and the best time for site disturbing activities.
  • February 1 – April 14 is early nesting season, a time to be aware of potential impacts and survey areas for active nests before conducting potentially disruptive activities.
  • April 15 – July 31 is primary nesting season, a time to avoid disturbance if at all possible and survey sites for active nests when potentially disrupting activities are unavoidable.

The City of Lake Oswego does not have authority to administer or enforce the Federal MBTA, but we all have a responsibility to avoid active nests and delay potentially disturbing activities until birds have fledged. Most birds will leave the nest within about two weeks.

Visit these resources to learn more about the MBTA, what to do if you find a baby bird out of its nest, landscaping for native bird habitat, and more:

 Please check back for more seasonal tree care and maintenance advice!

Link to Tree Care and Maintenance Archives


Fall 2021: Healthy Trees are Defended Trees

Special Edition: After the Storm

Winter 2021: What is an Arborist?

Fall 2020: Soil Management  

Summer 2020: Retaining and Creating Snags for Wildlife

Spring 2020: Mulch: Numerous Benefits and Easy Application

Winter 2020: Tree Planting: To Stake or Not to Stake?

Fall 2019: Insects and Diseases

​Summer 2019: Drought Stress Revisited

Spring 2019: Trees and Construction

Winter 2019: Topped Tree

Fall 2018: Autumn Leaves

Summer 2018: Emerald Ash Borer

Spring 2018: Pruning Young Trees

Winter 2017: Tree Related Storm Damage

Fall 2017: New Tree Selection and Planting

Summer 2017: Trees and Turfgrasses

Spring 2017: English Ivy Removal

Winter 2017: Recognizing Tree Risk

Summer 2016: Drought Stress

Fall 2016: Preparing Trees for Winter


Additional Tree Care Resources:

National Arbor Day Foundation The Morton Arboretum
Oregon Department of Forestry Tree Care Info
ISA Find an Arborist Alliance for Community Trees
Oregon Department of Forestry  


Right Tree in the Right Place

Use this handy guide for assistance in choosing the right species of tree based on the constraints of a site, such as overhead wires, narrow plant strips, and proximity to structures.

"Right Tree Right Place" - helpful information such as "Use this guide for assistance in choosing the right species of tree based on the constraints of a site, such as overhead wires, narrow plant strips, and proximity to structures."

"Master Plant List" - a guide to the plants that are acceptable for mitigation requirements in Lake Oswego.