Floating the egg is useful for some species. If the egg is more than ten days old and does not float, there is no viable embryo. More prolonged playback may distract subjects from activities that are essential to reproductive success. Unless required for the experiment, speakers should not be placed close to the nest, etc. Live decoys are frequently used in conjunction with playbacks.
Live decoys require particular attention in the field.
Birds used in this way should be trained for a day or so prior to onset of the experiment. An untrained bird tends to flail around the cage when placed on another's territory. A decoy habituated to housing in a cage under field conditions provides a more appropriate experimental stimulus and is also subjected to less stress. Note also that the decoy must be provided with food and water at all times. Avoid placing the decoy in exposed situations, especially on hot days.