Vocal Responses of Lambs To Sound Recordings of Ewe Bleats

A series of playback experiments were carried out on Dalesbred, Jacob and Border Leicester lambs at 7, 20 and 30 days old, to investigate when the lamb's vocal answering response developed. The lambs were tested one by one in a small pen, during which time they heard a recording of their own ewe's bleats and a recording of an alien ewe. Half the lambs heard their dam first and alien ewe second, the others heard the alien ewe first and their dam second. The vocalisations of the lambs were recorded on a tape recorder and later analysed to count the number of bleats made by the lambs in response to 10 ewe bleats. The time interval between bleats was measured and when the lamb bleats overlapped ewe bleats, the time from the start of the ewe bleat was also measured. The 7 day old lambs answered more bleats from their own ewes than alien, but there was no difference between the lamb's responses to own or alien ewe at 20 and 30 days. The lambs bleated rapidly in response to the ewe bleats often bleating before the ewe bleat had ended. These were named 'continuous' bleat responses and the time to respond varied from 0.51-0.69 sec. The 'timed' bleat responses were made after the ewe bleat was complete, and the interval between bleats varied at 7 days from 0.83 sec for Jacobs to 1.41 sec for Dalesbreds and 1.35 sec for Border Leicester lambs. The length of the response interval increased with age. The lambs made fewer 'continuous' bleat responses at 20 and 30 days than at 7 days. The failure to get any consistent difference in lamb vocal responses to own or alien ewe bleats was probably caused by putting the lambs into small pens, as previous results with free running lambs have shown that the lambs answer more to their own ewe.