|Vocal Development in Grasshopper Sparrow Nestlings|
|Rebecca A Hill, Bernard Lohr. University of Maryland, Baltimore County, Baltimore, MD, United States
Many nestling songbirds call to elicit feeding by adults. Physical development in the typical nestling songbird occurs rapidly. Small hatchlings grow to fledglings nearly the size of adults within a few days or weeks. Rapid syringeal development is likely to parallel changes in nestling size and should result in changes in the structure of begging calls. Few studies have examined changes in begging call development over the nestling phase. Grasshopper Sparrows (Ammodramus savannarum) have a nestling phase that lasts 8 to 9 days. We recorded calls from wild and laboratory-reared Grasshopper Sparrow nestlings and measured 21 call parameters. As nestlings aged, their calls increased in duration, peak frequency, and number of frequency and envelope modulations. Our results are generally consistent with those found in other studies. Duration increased in calls of all other species and peak frequency increased in half of those species. However, frequency modulations decreased in the few other species measured for that feature. Our results suggest that as nestlings grow the size and activity of the vocal apparatus and respiratory tract can support a longer, more complex call.