The shutter click made by a dSLR can disturb wildlife if you are close enough for it to be heard. As you can see in these three images, the male Downy Woodpecker shown here came closer and closer to locating me. I am sure it was the shutter click that attracted his attention. This three-image sequence was taken with my Olympus 70-300mm lens at the full zoomed-in 300mm (600mm equivalent field of view). Even then, I had to crop in Lightroom to get a reasonably tight composition.