Calling by domestic piglets: reliable signals of need?

TLDR: If a piglet's calls provide reliable information about its need for the sow's resources, then this calling can be used as a measure of its welfare, which is consistent with theoretical models of honst signalling.

About: This article is published in Animal Behaviour.The article was published on 1995-01-01 and is currently open access. It has received 179 citations till now.

Figures

Figure 5. The mean ( ± SE) number of calls with the frequency of the loudest band (a) less than 250Hz, (b) between 250 and 500Hz, (c) and greater than 500Hz, uttered during the first 16 s of each of five 1-min periods sampled. Results are combined from manipulations 1 and 2. Piglets that were 'unfed' and 'non-thriving' are included in the 'poor' condition, and piglets that were 'fed' and 'thriving' form the 'good' condition.'

Figure 2. The mean ( ± SE) number of calls uttered by piglets during the first, second, fourth, eighth and twelfth minutes of separation from the sow. (a) Results from manipulation 1 (long-term condition), comparing calls of piglets that were of high body weight and rapid weight gain ('thriving') with calls from litter-mates that were of relatively low body weight and slow weight gain ('non-thriving'). (b) Results from manipulation 2 (short-term condition), comparing calls of piglets that had just received milk ('fed') with calls from those that had just missed a milk ejection ('unfed').

Figure 4. The frequency distribution of data from a representative piglet for one call variable, frequency of the loudest band.

Figure 3. The mean ( ± SE) (a) duration, (b) frequency of loudest band, (c) weighted frequency, and (d) change in frequency, for calls uttered by piglets in 'poor' and 'good' conditions during the first 16 s of each of the five 1-min periods sampled. Results are combined from the two manipulations. Piglets that were 'unfed' and 'non-thriving' are included in the 'poor' condition, and piglets that were 'fed' and 'thriving' form the 'good' condition.

Figure 1. Sonagram of a 1-s section from one of the five 30-s sequences of isolation calls used as stimuli in the playback experiment.

Frequently asked questions

Q1. What have the authors contributed in "Calling by domestic piglets: reliable signals of need?" ?

In both cases, the aim was to manipulate the piglet 's need for the sow 's attention. Research on the behaviour of animals has helped to develop a number of approaches to the assessment of animal well-being ( Dawkins 1980, 1990 ; Fraser & Broom 1990 ). The idea that an animal 's vocalizations can provide information about its state or condition has some intuitive appeal, but two elements are required before this assumption can be added to the repertoire of techniques for welfare assessment. At a minimum, for the animal and call being studied, some aspect of vocal behaviour must change in a consistent way with the animal 's condition. This framework will also allow us to address more general issues, such as why an animal should signal, why signals should provide reliable information about the signaller 's needs, and why other animals might respond to these signals. In the last three cases, calling provides a reliable indicator of need/condition and can potentially provide both the sow and ourselves with information about piglet well-being. Their observations of natural interactions suggested that sows respond to calling piglets by approaching them and by vocalizing themselves. For piglets to gain some advantage from calling, these calls must affect the behaviour of potential receivers. 

Q2. How many error degrees of freedom did one subject have to be removed from the analyses?

One subject did not call during one of the 1-min periods and was removed from all analyses involving spectrographic measurement, resulting in 26 error degrees of freedom for these analyses. 

Q3. How do sows respond to isolation calls?

In the wild, sows return to a kin group once their litter is approximately 10 days of age (Newberry & Wood-Gush 1985; Jensen & Redbo 1987). 

Q4. How long did the piglets stay in the enclosures?

After the piglets were placed in the enclosures, the tape-recorder was started and the two piglets were recorded simultaneously for 13 min. 

Q5. What is the effect of isolation calls on sows?

Results from an on-going experiment indicate that sows do show a much stronger response to extreme calls from needy piglets than to lower-frequency, shorter-duration and lower-call-rate sequences from less needy litter-mates (unpublished data). 

Q6. Why did the piglets differ in their vocal behaviour?

In the first manipulation, any differences in the vocal behaviour of the two piglets could reflect fixed differences between individuals: large piglets might call differently from small piglets not because they are in less need, but just because they are large.