An endangered bird calls less when invasive birds are calling

Novel noises can affect various animal behaviours, and changes to vocal
behaviour are some of the most documented. The calls of invasive species
are an important source of novel noise, yet their effects on native
species are poorly understood. We examined the effects of invasive bird
calls on the vocal activity of an endangered Australian finch to
investigate whether: (i) native finch calling behaviour was affected by
novel invasive bird calls, and (ii) the calls of the finches overlapped in
frequency with those of invasive birds. We exposed a wild population of
Black-throated Finch southern subspecies (Poephila cincta cincta) to the
vocalisations of two invasive birds, Nutmeg Mannikins (Lonchura
punctulata) and Common Mynas (Acridotheres tristis), a synthetic ‘pink’
noise, and a silent control. To determine whether the amount of
Black-throated Finch calling differed in response to treatments, we
recorded and quantified Black-throated Finch vocalisations, and assessed
the amount of calling using a generalised linear mixed model followed by
pairwise comparisons. We also measured, for both Black-throated Finches
and the stimulus noises: dominant, minimum and maximum frequency, and
assessed the degree of frequency overlap between Black-throated Finch
calls and stimulus noises. Compared to silent controls, Black-throated
Finches called less when exposed to Common Myna calls and pink noise, but
not to Nutmeg Mannikin calls. We also found that pink noise overlapped
most in frequency with Black-throated Finch calls. Common Myna calls also
somewhat overlapped the frequency range of Black-throated Finch calls,
whereas Nutmeg Mannikin calls overlapped the least. It is possible that
masking interference is the mechanism behind the reduction in calling in
response to Common Myna calls and pink noise, but more work is needed to
resolve this. Regardless, these results indicate that the calls of
invasive species can affect the behaviour of native species, and future
research should aim to understand the scope and severity of this issue.