An automated method of estimating the spatial distribution of piglets within a pen was used to assess huddling behaviour under normal conditions and during a febrile response to vaccination. The automated method was compared with a manual assessment of clustering activity. Huddling behaviour was partly related to environmental conditions and clock time such that more huddling occurred during the night and at lower ambient air temperatures. There were no positive relationships between maximum pig temperatures and environmental conditions, suggesting that the narrow range of air temperatures in this study was not a significant factor for pig temperature. Spatial distribution affected radiated pig temperature measurements by IR thermography. Higher temperatures were recorded in groups of animals displaying huddling behaviour. Huddling behaviour was affected by febrile responses to vaccination with increased huddling occurring 3 to 8 h post-vaccination. The automated method of assessing spatial distribution from an IR image successfully identified periods of huddling associated with a febrile response, and to changing environmental temperatures. Infrared imaging could be used to quantify temperature and behaviour from the same images.

The objective of this study was to investigate the effect of infrared (IR) temperature on thermoregulatory behaviour in suckling piglets in the first 3 weeks after farrowing. A total of 10 piglets from each of the 16 litters were exposed to recommended IR temperature conditions at 1, 2 and 3 weeks of age, with a mild offset (4°C) in IR temperature during the first experiment and a more challenging offset (8°C) during the second experiment. Digital photos were taken when all piglets had settled in the creep area, and the lying posture and huddling behaviour were analysed. A lying posture score and a huddling score was calculated by multiplying the number of piglets in each category with a given value for each category, based on different lying postures and different degrees of huddling behaviour. With a 4°C change in IR temperature, the piglets tended to alter their lying posture, while an 8°C change had a significant effect on lying posture (P < 0.01). A change in IR temperature of 4°C had no effect on the degree of huddling. The huddling score decreased significantly with 8°C change in IR temperature (P < 0.05). Postural changes, rather than changes in degree of huddling were the preferred thermoregulatory strategy for suckling piglets.

Circadian rhythms of metabolic rate and body temperature were measured in groups of huddling and solitary red-billed woodhoopoes (Phoeniculus purpureus) as a function of ambient temperature. Basal metabolic rates were 30-60% lower than those of similar-sized birds of other species. As a consequence, circadian amplitudes of Tb and VO2 fluctuation between the rest and activity phases of non-huddling birds were also larger than expected. Circadian rhythms of metabolism save huddling and non-huddling woodhoopoes 19-34% of their potential daily energy expenditure. Birds huddling in groups conserved 12-29% of the daily energy expenditure of non-huddling birds at ambient temperatures of 20°C and below. However, at 30°C huddling birds used c. 12% more energy than non-huddling birds. The various avenues of energy conservation employed by woodhoopoes are suggested to be beneficial in: a) augmenting the proximate benefits of cooperative breeding; and b) optimizing fitness in the drought-prone sub-Saharan savannahs which are heavily influenced by the El Niño Southern Oscillations.