Reuse of nests in the Great Reed Warbler Acrocephalus arundinaceus: A behavior to save time and energy and to deter nest parasites?

The reproductive period in animals is a demanding part in their life history. In birds, environmental factors, such as adverse weather, predation, or brood parasitism; and/or anthropogenic disturbance, can limit breeding success, resulting in failure of clutches. The nest loss in open-cup nesting passerines is usually replaced with a new nest with a new clutch, however, in some cases the clutch replacement may occur in unusual forms. In this study, we report on three cases of within-season nest reuse in the Great Reed Warbler. In the first case, a nest was reused for two times in the same season after unsuccessful nesting attempts (two-time nest reuse). After the nest was depredated the first time, the female laid new eggs that were depredated again, then again the female laid new eggs that produced four fledglings. In the second case, the first clutch was depredated, after which the female laid a new clutch in the same nest that was again depredated. In the third case, the female laid new eggs among the eggs that failed to hatch previously. Our observations tend not to be consistent with the predator avoidance hypothesis because the depredated nests were reused by the parents. The time/energy saving hypothesis or possible deterrence of nest parasitism could explain nest reuse in this study, but because of low number of nests reused compared to the total number of nests found, this phenomenon needs further clarification.