Signal plasticity is a building block of complex animal communication systems. A particular form of signal plasticity is the Lombard effect, in which a signaler increases its vocal amplitude in response to an increase in the background noise. The Lombard effect is a basic mechanism for communication in noise that is well-studied in human speech and which has also been reported in other mammals and several bird species. Sometimes, but not always, the Lombard effect is accompanied by additional changes in signal parameters. However, the evolution of the Lombard effect and other related vocal adjustments in birds are still unclear because so far only three major avian clades have been studied. We report the first evidence for the Lombard effect in an anseriform bird, the mallard (Anas platyrhynchos). In association with the Lombard effect, the fifteen ducklings in our experiment also increased the peak frequency of their calls in noise. However, they did not change the duration of call syllables or their call rates as has been found in other bird species. Our findings support the notion that all extant birds use the Lombard effect to solve the common problem of maintaining communication in noise, i.e. it is an ancestral trait shared among all living avian taxa, which means that it has evolved more than 70 million years ago within that group. At the same time, our data suggest that parameter changes associated with the Lombard effect follow more complex patterns, with marked differences between taxa, some of which might be related to proximate constraints..