Birds hitting your windows during fall migration: what works on a GTA house

Birds hitting your windows is at its most noticeable in the GTA between late August and early November, when migrants are moving along the Lake Ontario shoreline. The fix that works on a house is finding the one or two panes that reflect trees or sky, treating the outside of that glass so a bird reads it as solid, and changing what sits near it. This guide covers what the City of Toronto, FLAP Canada and the Canadian Wildlife Health Cooperative actually recommend, and what to do when a bird has already hit.

Why do birds hit house windows in the autumn?

Birds hit glass because they see a flight path in it: either a reflection of open sky or vegetation, or a clear view through the glass to plants or sky on the other side. The Canadian Wildlife Health Cooperative (CWHC) describes collisions this way, and adds that nocturnal migrants often fly into windows following a light source.

Autumn adds volume. The City of Toronto puts fall migration from mid-August to the beginning of November, and describes the Toronto area, on the Lake Ontario shoreline where two major flyways converge, as an important rest stop through which millions of birds travel. Most of them migrate at night. Oakville, Burlington and Mississauga sit on the same shoreline, although the dates above are Toronto's own.

Houses matter more than towers here. The estimate most Canadian sources use, from Machtans and colleagues (2013), is about 25 million birds a year killed by window collisions in Canada, and FLAP Canada states that 90% of these collisions are thought to happen at single-family homes.

Which windows on a house are the ones birds hit?

The windows that get hit are usually the ones that look like open space from outside. Toronto's Best Practices for Bird-Friendly Glass identifies the patterns, and they translate directly to a house:

• Glass that reflects trees and shrubs. Toronto's guide states that glass reflecting shrubs and trees causes more collisions than glass reflecting pavement or grass. A picture window facing a hedge or a treed backyard fits this description.
• See-through conditions. Glass corners, glass railings, and windows on opposite walls of a room let a bird see sky or greenery straight through the house. A sunroom or a living room with windows front and back does this.
• Large single panes. The same guide notes that picture windows on private homes have increased collisions, and contrasts them with older windows divided into small panes and often fitted with exterior insect screens.
• Windows near a feeder or bath. Toronto cites feeder studies showing collisions become fatal when birds fly toward glass from more than a few feet away.
• Windows lit at night. A lit room, or an exterior floodlight shining across glass, draws night migrants toward the house.

To find yours, walk the outside of the house on a bright morning and look at each pane from roughly where a bird would approach: the garden, the hedge line, the feeder. The panes that show a clean reflection of trees or sky, or that you can see straight through, are the ones to treat first. FLAP recommends exactly this order: assess, then treat the priority windows first rather than every pane in the house.

What actually stops birds hitting a window?

What works is a pattern across the whole outside surface of the glass, dense enough that a bird does not try to fly through the gaps. A single sticker does not work. FLAP Canada, CWHC and Toronto's guide agree on the principle and differ slightly on the numbers, so the table puts them side by side.

For a house, the 5 x 5 cm figure is the one to work to: it is the strictest of the three and the only one stated as protecting birds of every size, including hummingbirds and kinglets. Every source puts the markers on the outside of the glass, because a pattern on the inside is hidden behind the very reflection that causes the problem.

The options, from cheapest to most permanent

1. Soap or tempera paint patterns. CWHC and FLAP both list them. FLAP notes a soap or highlighter pattern may need repeating after every rainfall, which makes it a stopgap for the rest of migration rather than a fix.
2. Strips of tape or dot decals applied to the outside at the spacing above. FLAP lists products sold for this purpose, such as Feather Friendly tape.
3. Cords hung in front of the window (the Acopian BirdSaver design). FLAP's DIY guide mounts 1/8-inch paracord from a length of aluminium J channel on the outer frame, spaced 4 inches apart or closer. FLAP priced a standard patio door at about $28 in materials.
4. Exterior screens, shutters or netting. CWHC lists them as physical barriers; FLAP adds that shutter slats left open must still meet the spacing.
5. Patterned or bird-safe glass when a window is being replaced anyway. FLAP lists fritted, printed and bird-screen products worth asking about when a window is due for replacement.

The two applied options need a clean, dry pane to stick. Read the package for the product's minimum application temperature before you plan the job for a cold October morning, and treat an upper-floor window from a stable ladder or not at all; the ladder rules are in exterior window cleaning on a two-storey house.

What does not work

• One or two hawk or falcon silhouettes. Toronto's guide states that bird-of-prey silhouettes have been tested and found largely ineffective. FLAP explains why: birds are not frightened by the shape, and they fly around it into the untreated glass beside it.
• Anything on the inside of the glass. Toronto no longer accepts interior screens as a strategy, because of their variable distance from the glass and the lack of evidence that they work.
• Tinted glass. Toronto's guide says there is no evidence that tinted glass reduces collisions.

The screen and cleaning trade-off in autumn

Two pieces of standard autumn window advice pull against bird safety, and it is better to know that before you do them. FLAP's homeowner page advises leaving exterior screens where they are, because a screen mutes the reflection in the glass behind it. It also states that collisions increase when windows are sparkly clean, because even a little dust reduces reflection.

Neither means leaving the house dirty or the screens on all winter. Our guide to taking window screens off before winter explains why the screens come out and what that inspection catches. The practical order for a house with a problem window is:

1. 1Identify the one or two windows that get hitLook for the pane that reflects trees or sky, or that you can see straight through. Everything else can be cleaned and have its screen removed on the usual schedule.
2. 2Leave that window's screen in until migration ends, or mark the glassToronto puts the end of fall migration at the beginning of November. If you would rather take the screen out, apply tape or decals to the outside of that pane at 5 x 5 cm spacing before you do.
3. 3Clean first, mark secondAdhesive markers go on clean, dry glass, so the exterior clean comes before the tape. Once they are on, the pane can be cleaned around them and stays safe however clear it is.
4. 4Tell whoever cleans the windows which panes carry markersTape and dots on the outside surface need to be worked around rather than scraped off.

Feeders, houseplants and lights

Feeders and baths should be either very close to the glass or well away from it. BirdSafe advises less than half a metre, so a bird leaving the feeder cannot build enough speed to be hurt if it hits. CWHC gives a wider rule: within 1 metre, or beyond 10 metres, where birds can recognise the window as a reflection. Anywhere in between is the zone to avoid.

• Move houseplants away from windows; a plant seen through the glass is a target. FLAP also suggests drawing blinds during the day with the slats turned open.
• Turn off exterior floodlights at night during migration and draw shades on lit rooms. Toronto recommends outdoor lighting directed downward, with minimal spill beyond the area that needs light.
• Keep tall shrubs from being the main thing a large pane reflects, if you are planting this autumn anyway.

What to do when a bird has hit your window

Keep cats and people away, and get advice from an authorized wildlife rehabilitator before doing more. Ontario's guidance is that only wildlife custodians may provide temporary care to injured wildlife, that you should not approach or try to capture a wild animal without first talking to one, and that you may hold a sick or injured wild animal for up to 24 hours only while transferring it to a custodian or a veterinarian. The province lists custodians on its Find a wildlife rehabilitator page.

If you are told to contain the bird, or it is in immediate danger, the City of Toronto and CWHC describe the same method:

1. Place the bird in a cardboard box or an unwaxed paper bag, with tissue inside to give it a perch, and close it.
2. Put it somewhere dark and quiet, away from people and pets.
3. Do not give it food or water, and handle it no more than necessary.
4. Wear gloves. Ontario notes wild animals can carry diseases such as avian influenza, and advises washing your hands with soap and warm water afterwards.
5. Follow the custodian's instructions on whether and when to release it. CWHC's fact sheet says a bird with visible injuries such as bleeding, a drooping wing or a beak injury should go to a rehabilitator as quickly as possible.

A dead bird can be reported to the Canadian Wildlife Health Cooperative, which Ontario asks the public to use for sick or dead wildlife (1-866-673-4781). FLAP also runs a community mapper for collision reports.

When this is a job to do yourself

Almost all of it is. Finding the problem pane, moving a feeder, switching off a floodlight and taping a ground-floor window are an afternoon's work with no special tools. The parts worth handing over are the upper-floor panes you cannot reach safely from a ladder, and the general exterior clean that should come before any adhesive goes on. If you book that clean before the end of migration, mention which windows you plan to mark so they can be done first. When the markers are on, the timing of the rest is covered in the last exterior window clean of the year.