A wild bird trapped in your chimney can be difficult to remove, but there is one simple method that can be used to remove the bird without harming it.
Measure the length and width of the chimney flue opening at rooftop level.
Transfer these measurements to the 1/4" X 2' X 2' cardboard sheet and draw a second line 1 inch inside the perimeter of the original lines.
Cut cardboard to the measurements of the inner line using craft/utility knife.
Drill four holes one inch inside of each corner of the cardboard rectangle.
Cut string into four equal lengths equal to the chimney height as measured from the ground to top of flue opening.
Thread one string through each of the four holes and tie knot to secure in place.
Holding two of the four strings lower cardboard sheet in a vertical position into and down the chimney flue until it hits the damper plate in the bottom of the chimney.
Shine flashlight down the chimney to observe the position of the bird and slowly lower the cardboard from a vertical to a horizontal position by relaxing the tension on the two strings used to lower the sheet into the chimney while holding onto all four strings. Once completely lowered, the cardboard sheet will being lying flat on the damper box.
Wait ten or more minutes to give the bird time to calm down, at which point it will settle onto the cardboard sheet.
Gently and very gradually apply equal tension to each of the four strings and begin slowly raising the cardboard sheet up from its resting position on the damper plate. The rate of lift should be no greater than one to two inches per minute.
Use a helper to shine flashlight down into the chimney to monitor the bird's position on the cardboard. Hold in place if the bird is agitated or fighting the rate of rise of the cardboard.
Continue to slowly raise the cardboard platform and the bird until they are within two to three feet of the chimney opening and then hold in place and continuing to hold all four strings evenly back away from the opening and allow the bird free flight. Should the bird not fly, raise the platform another foot until it does.
If the bird is injured and unable to fly it should be taken to the nearest wildlife veterinarian. Chimneys and flues have many different designs. This procedure works best when the flue pipe is of uniform size from the top of the chimney to the damper box. In chimneys in which the flue opens to a wider width just above the damper box, the cardboard platform will not completely fill and seal off openings around the perimeter of the platform, allowing the bird to get under the platform as it rises. This can be avoided by raising the platform very slowly for the first two or three feet, at which point the flue becomes uniform in size and the sides are sealed.