![]() ![]() ![]() Woodpecker drumming sounds, which may also serve as communication signals, are generally lower in frequency and broader in bandwidth than vocal signals, and may overlap with the frequencies typical of vocalizations ( Winkler and Short, 1978 Short, 1982 Jackson, 1994 Mahan, 1996 Shackelford et al., 2000 Jackson and Ouellet, 2002 Jackson et al., 2002). This frequency span is similar to that of other small–medium-sized birds ( Fay, 1988 Dooling et al., 2000). In small woodpeckers, vocal signals have most energy in the frequency range 1–6 kHz ( Winkler and Short, 1978 Jackson, 1994 Mahan, 1996 Jackson and Ouellet, 2002 Jackson et al., 2002). The peak power in the vocal signals of many species corresponds with the most sensitive part of the audiogram. Vocalizations in small birds are often correlated with auditory ability ( Dooling et al., 2000). The ABR and other evoked-potential techniques are particularly useful as a means of estimating auditory sensitivity because training of animals is not required, making these techniques faster and more efficient than behavioral tests. Numerous studies now have examined the ABR specifically in birds, and it has proven a reliable technique for estimating basic auditory sensitivities across a range of species ( Dooling and Walsh, 1976 Aleksandrov and Dmitrieva, 1992 Dmitrieva and Gottlieb, 1992 Brittan-Powell et al., 2002, 2005, 2010 Higgs et al., 2002 Lucas et al., 2002 Brittan-Powell and Dooling, 2004 Wright et al., 2004 Henry and Lucas, 2008, 2009 Noirot et al., 2011). The ABR technique is also advantageous because the morphology of the ABR waveform is conserved in most vertebrates (e.g., Corwin et al., 1982 Walsh et al., 1992). The derived audiogram is a good approximation of the shape of behavioral audiograms but does not necessarily predict absolute auditory sensitivity (e.g., Borg and Engström, 1983 Wenstrup, 1984 Stapells and Oates, 1997 Brittan-Powell et al., 2002, 2010). The ABR is a useful tool for studying the functionality of the auditory system in a wide variety of animals (e.g., Jewett, 1970 Corwin et al., 1982 Walsh et al., 1986 Burkard and Voigt, 1989 Donaldson and Rubel, 1990 Mills et al., 1990 Burkard et al., 1996 McFadden et al., 1996 Kenyon et al., 1998 Liu and Mark, 2001 Higgs et al., 2002). We used the auditory brainstem response (ABR) as a means of estimating hearing ability in woodpeckers. As a consequence, these adaptations to dampen mechanical shock during pecking could play a role in shaping the hearing sensitivities of these birds. This adaptive morphology involves unique modifications of the ear anatomy and musculature that include a narrowed round window and a specialized dual columellar footplate that, coupled with the round window membrane, may act to reduce transient force on the cochlear fluids ( Kohllöffel, 1984). Because of these adaptations, a woodpecker's brain is protected from impact and vibration injury ( Bock, 1964 May et al., 1976, 1979). Woodpeckers are a unique group of birds that exhibit a number of specialized cranial adaptations serving to dampen forces on the bill and skull ( Beecher, 1953 Bock, 1964, 1966 Spring, 1965). While there are numerous behavioral and physiological studies of auditory abilities in small birds, woodpeckers have been a neglected group in terms of their basic hearing ability. ![]()
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