- Email: [email protected]
Strategies and tactics in foraging — The pursuit of the eatable
85 attacks received. Their interruptions were also longer (36.2 against 19.2 s). Finally, the dominant sows generally finished feeding later (1504.8 against 1323.9 s, respectively). This research was supported by grants from the Italian Ministero Pubblica Istruzione and Consiglio Nazionale delle Ricerche.
Sow Behaviour in Computerised Feeding Systems T.G. KNOWLES, J.C. EDISON, A.T. VRANCH and P.H. BROOKS
Seale Hayne College, Newton Abbot, Devon TQ12 6NQ, Gt. Britain
ABSTRACT Computerised dry sow feeding systems are becoming increasingly popular as an alternative to earlier husbandry systems, partly in order to overcome some of the welfare problems associated with tethered sow systems. In order to investigate the feeding behaviour of dry sows in such a system, to see whether it may give rise to any welfare problems of its own, an interface has been developed between a system with two feeding stations ("Pig Code") and a microcomputer data collection system recording the amount of food eaten and the time and duration of every visit. Data collected over a 2°month period showed a regular diurnal variation in visits to feeding stations. A peak in visiting frequency coincided with the start of the daily feeding cycle at 07:05 a.m. (GMT). This was composed of a sharp rise in the frequency of non-feeding visits during the 2 h before the start of the feeding cycle, followed by an even sharper and more sustained increase in frequency of feeding visits when the new cycle started. The animals used the two feeding stations to unequal extents. The causes underlying these results have yet to be established.
Strategies and Tactics in Foraging of the Eatable
The Pursuit
A.W. ILLIUS
Department of Agriculture, University of Edinburgh, West Mains Road, Edinburgh EH9 3JG (Gt. Britain)
ABSTRACT Optimal foraging theory provides a framework for the analysis of foraging behaviour. Foraging strategies are part of a hierarchy of strategic goals which contribute eventually to the lifetime
86 reproductive success of individuals. Foraging tactics are those processes of perception, food choice and handling whereby animals express foraging drives. They have evolved as complex adaptations to the nutritional environment, but constitute only an indirect means of achieving strategic goals. Three examples illustrate this. The size of a grazing animal in relation to the height of the sward exerts a powerful influence on selection of the grazing niche, due to the effect of grazing mechanisms on intake rate. A test of a foraging model which predicts the grazing behaviour of cattle showed that the rate of encounter of different classes of herbage influences diet selection, but the diet contained less energy than the maximum attainable. When sheep were offered a choice between swards differing in height and clover content, they tended to choose the sward offering the highest rate of herbage intake. However, in any test, intake rate was a very poor predictor of choice, instead herbage height seemed to be the most importance cue. Thus, they appeared to respond to a variable correlated with intake rate rather than responding to instantaneous intake rate, and were therefore pursuing a tactical rather than strategic goal. Foraging tactics may define behavioural responses more clearly than a strategic definition of foraging goals.
Choices Facing Foraging Red Grouse C.J. SAVORY
AFRC Institute for Grassland and Animal Production, Poultry Department, Roslin, Midlothian EH25 9PS (Gt. Britain)
ABSTRACT The feeding ecology of grouse was studied for 3 years on a moor in N.E. Scotland where the heather had been burned regularly in small patches to maintain high grouse stocks. The birds ate mainly heather and thus had a range of ages and heights of heather on which to feed. They ate steadily throughout the day, but more intensively in the evening, when amounts stored in their crops depended on the length of night. Judging from the distribution of their droppings, they spent the most time on heather patches aged 2-5 years (10-25 cm) in spring, 4-7 years (20-32 cm) in summer, 3-6 years (15-28 cm) in autumn, 4-8 years (20-37 cm) in winter, and more time near the edges of patches on some age classes. They could not be watched in summer, when they were secretive, but counts of their pecking rates at other times showed that they ate mainly 2-5-yearold heather in spring, 3-5-year-old in autumn and 3-8-year°old in winter. These preferences were related to the heather's height (a standing grouse is 30 cm high, a squatting one 15 cm), percent ground cover and food value (young heather being more nutritious than old). Judging from analyses of crop contents, they ate particles 5-15 mm long, 74% (mean) of which were shoot tips and the rest bitten at both ends, and selected for (i.e., more in crop heather than in samples picked at feeding sites) nitrogen and phosphorus (the two nutrients in shortest supply relative to their requirements), but not for energy or other nutrients. Selection for N and P was correlated negatively with both feeding rate (as indicated by the weights of crop contents) and mean weight of particles eaten. They preferred to feed on 3-year-old heather in the evening and ate more 2- and 3-year-old heather in spring than at other times. It is concluded that all seasonal and diurnal variation in the utilisation of heather by grouse can be accounted for by variation in their need for: (a) feeding at a certain rate; (b) selecting particular
Sow Behaviour in Computerised Feeding Systems T.G. KNOWLES, J.C. EDISON, A.T. VRANCH and P.H. BROOKS
Seale Hayne College, Newton Abbot, Devon TQ12 6NQ, Gt. Britain
ABSTRACT Computerised dry sow feeding systems are becoming increasingly popular as an alternative to earlier husbandry systems, partly in order to overcome some of the welfare problems associated with tethered sow systems. In order to investigate the feeding behaviour of dry sows in such a system, to see whether it may give rise to any welfare problems of its own, an interface has been developed between a system with two feeding stations ("Pig Code") and a microcomputer data collection system recording the amount of food eaten and the time and duration of every visit. Data collected over a 2°month period showed a regular diurnal variation in visits to feeding stations. A peak in visiting frequency coincided with the start of the daily feeding cycle at 07:05 a.m. (GMT). This was composed of a sharp rise in the frequency of non-feeding visits during the 2 h before the start of the feeding cycle, followed by an even sharper and more sustained increase in frequency of feeding visits when the new cycle started. The animals used the two feeding stations to unequal extents. The causes underlying these results have yet to be established.
Strategies and Tactics in Foraging of the Eatable
The Pursuit
A.W. ILLIUS
Department of Agriculture, University of Edinburgh, West Mains Road, Edinburgh EH9 3JG (Gt. Britain)
ABSTRACT Optimal foraging theory provides a framework for the analysis of foraging behaviour. Foraging strategies are part of a hierarchy of strategic goals which contribute eventually to the lifetime
86 reproductive success of individuals. Foraging tactics are those processes of perception, food choice and handling whereby animals express foraging drives. They have evolved as complex adaptations to the nutritional environment, but constitute only an indirect means of achieving strategic goals. Three examples illustrate this. The size of a grazing animal in relation to the height of the sward exerts a powerful influence on selection of the grazing niche, due to the effect of grazing mechanisms on intake rate. A test of a foraging model which predicts the grazing behaviour of cattle showed that the rate of encounter of different classes of herbage influences diet selection, but the diet contained less energy than the maximum attainable. When sheep were offered a choice between swards differing in height and clover content, they tended to choose the sward offering the highest rate of herbage intake. However, in any test, intake rate was a very poor predictor of choice, instead herbage height seemed to be the most importance cue. Thus, they appeared to respond to a variable correlated with intake rate rather than responding to instantaneous intake rate, and were therefore pursuing a tactical rather than strategic goal. Foraging tactics may define behavioural responses more clearly than a strategic definition of foraging goals.
Choices Facing Foraging Red Grouse C.J. SAVORY
AFRC Institute for Grassland and Animal Production, Poultry Department, Roslin, Midlothian EH25 9PS (Gt. Britain)
ABSTRACT The feeding ecology of grouse was studied for 3 years on a moor in N.E. Scotland where the heather had been burned regularly in small patches to maintain high grouse stocks. The birds ate mainly heather and thus had a range of ages and heights of heather on which to feed. They ate steadily throughout the day, but more intensively in the evening, when amounts stored in their crops depended on the length of night. Judging from the distribution of their droppings, they spent the most time on heather patches aged 2-5 years (10-25 cm) in spring, 4-7 years (20-32 cm) in summer, 3-6 years (15-28 cm) in autumn, 4-8 years (20-37 cm) in winter, and more time near the edges of patches on some age classes. They could not be watched in summer, when they were secretive, but counts of their pecking rates at other times showed that they ate mainly 2-5-yearold heather in spring, 3-5-year-old in autumn and 3-8-year°old in winter. These preferences were related to the heather's height (a standing grouse is 30 cm high, a squatting one 15 cm), percent ground cover and food value (young heather being more nutritious than old). Judging from analyses of crop contents, they ate particles 5-15 mm long, 74% (mean) of which were shoot tips and the rest bitten at both ends, and selected for (i.e., more in crop heather than in samples picked at feeding sites) nitrogen and phosphorus (the two nutrients in shortest supply relative to their requirements), but not for energy or other nutrients. Selection for N and P was correlated negatively with both feeding rate (as indicated by the weights of crop contents) and mean weight of particles eaten. They preferred to feed on 3-year-old heather in the evening and ate more 2- and 3-year-old heather in spring than at other times. It is concluded that all seasonal and diurnal variation in the utilisation of heather by grouse can be accounted for by variation in their need for: (a) feeding at a certain rate; (b) selecting particular