Light Cycle Controlled Weight Changes in Pigeons
W. L. Palya*
Frequently motivational aspects of behaviour are standardized by maintaining animals at a percentage of their free feeding weight. Factors which affect free feeding weights, such as rhythmicity in eating, are therefore important. Various studies are available which suggest that feeding in various animals is not equally distributed across a day (Rusak and Zucker, 1975). Eating and presumably body weight vary with respect to the light/dark (L/ D) cycle. It is important then to determine the effect of the light cycle on the body weight within days. The present study observed weight changes within each day, during both continuous illumination and during days which provided a light and a dark period.
SUBJECTS: Twenty-nine Palmetto white King pigeons of undetermined sex from three to five months old were used.
APPARATUS: The pigeons were housed in standard commercial 30 x 45 x 45 cm open wire "laying cages". Individual coop cups were used to contain the water, and grain mixed with grit. The cages were located in a room approximately three meters square facing south toward a window with a closed venetian blind. The venetian blind diffused but did not eliminate sunlight. The approximate coordinates of the room were 32deg. 22' North Latitude and 82deg. 47' West Longitude. The study was conducted from January 25, 1971 (with an approximate sunrise of 07.00 hr and sunset of 17.03 hr) to March 18, 1971 (with an approximate sunrise of 06.32 hr and sunset of 17.45 hr). The laboratory which was adjacent to the pigeon room was typically active from 08.00 hr until 02.00 hr daily. Temperature was maintained between 18deg. and 24deg.C by a common building wide heating system.
PROCEDURE: Upon arrival the pigeons were housed in individual cages; and had free access to mixed grain (Purina Pigeon Top Flight Grains), red grit, (J. W. Williamson Co.) and water. Care was taken to maintain fresh water and nearly full food cups. Cups were inspected every 3 hrs during the weighing period. All pigeons were given the standard mixed grain regardless of any marked preferences.
Phase 1: All pigeons were on a free feeding baseline for 21 days. They were weighed at 3-hr intervals beginning at 08.00 hr and continuing until and including 02.00 hr. The fluorescent lights in the pigeon room remained on 24 hrs a day.
Phase 11: The pigeon room lights were turned off at 02.00 hr and the pigeon room remained dark until it was illuminated with sunlight from sunrise until 08.00 hr when the room lights were turned on. The pigeons continued to have free access to grain and to be weighed every 3 hrs. This phase was continued for 21 days.
Phase 111: This phase was a return to the baseline conditions of Phase 1. The room lights again remained on 24 hrs a day. Free access to grain was provided and weighing continued to take place every 3 hrs from 08.00 hr until 02.00 hr. This return to continuous illumination was maintained for 4 days.
Phase I V: The lights remained on 24 hrs a day, however food cups were removed each night at 02.00 hr and replaced at 08.00 hr. The birds continued to be weighed every three hours from 08.00 hr until, and including, 02.00 hr. This phase was continued for six days, at which time the standard mixed grain supply was exhausted.
The weight records of five representative birds are presented in Figure 1. The bird numbers appear above each record. All 29 birds showed virtually identical circadian changes.
During the baseline, there was 24 hrs a day illumination and access to food. Small unsystematic fluctuations in the weights occurred within each day. In spite of these changes most pigeons maintained relatively stable weights over the 21 days, however a few showed systematic long term changes in body weights of as much as 7%, as is shown in bird 22 which varied 40 g. Bird 22 exhibited a slow trend while bird 16 exhibited shorter duration trends.
The condition which provided a period of darkness but maintained free access to food 24 hrs a day controlled different behaviour. The daily weight curves for all birds indicated a dramatic increase in weight in the 3-to 6-hr period immediately before the lights were turned out. This effect was noticeable within a few days, stable within birds, and comparable across birds. These daily, acute changes in weight were abolished within approximately 4 days when the room was again illuminated 24 hrs a day. The daily abrupt increase in weight was not reacquired within the six days during which the food cups were removed at 02.00 hr and replaced at 08.00 hr. Some birds however did show a disproportionately large weight gain in the morning after the food cups were again available. Unfortunately the data were insufficient to demonstrate a substantial effect.
It is apparent that daily weight changes are entrained by the light cycle, and that this effect is acquired or abolished relatively quickly. The effect of the L/D cycle is to potentiate the weight gain in the hours immediately before the dark period.
The present study assessed circadian feeding behaviour by observing weight changes as its dependent measure. Other measures have been used. Duncan and Hughes (1972) used the weight loss of a food reservoir, while Zeigler et al. ( 1971) used pecks at the food reservoir; the results present a consistent picture. In domestic fowl and pigeons feeding occurs primarily just before the dark cycle.
Several proposals could be advanced which would account for this effect without appeal to the notion of a Zeitgeber or a cyclic environmental influence which controls the period of the behaviour. It could be that feeding occurs once every 24 hrs and was only spuriously correlated with the interval immediately preceding the dark cycle. This is unlikely in that the pronounced weight increase did not occur during the continuous illumination cycle. In addition both Duncan and Hughes (1972) and Zeigler et al. (1971) have also demonstrated feeding concentrated in the period preceding the dark cycle.
Alternatively, it is possible that the effect was caused by the periodic "unavailability" of food and that it was not a direct effect of the regularly changing light cycle. During a dark cycle pigeons roost and tend to be inactive. This may essentially preclude feeding. It could therefore be argued that the pre-dark cycle eating was controlled by a mechanism similar to facilitation during a signal which precedes a decrease in reinforcement frequency ( Pliskoff, 1961; Gibson and Milby, 1970). That is, accentuated feeding occurred in response to the temporally signaled subsequent unavailability of food.
This interpretation also seems unlikely. Food removal did not produce the same effect as the removal of light in Phase 11. It is possible that after a longer exposure some feeding patterns would emerge with the periodic removal of food cups. However, the main issue is that food removal is not equivalent to the removal of light. If anything, the short phase during which the food cups were removed from 02.00 hr until 08.00 hr suggest that food removal may generate most feeding at the onset of food availability not immediately before its removal.
The accentuated weight gain occurred when there was a light and dark period but did not occur in continuous illumination, even though the available external stimuli at the onset of feeding and even the immediately preceding 12 hrs were identical for both conditions. Various stimuli with a 24-hr period were available and could have served to concentrate feeding to one time period. The pigeons were housed in a common animal room and were therefore exposed to daily variations in laboratory activity, temperature and humidity, and even in the amount of sunlight diffusing through the venetian blind. However, a period of darkness was necessary to produce the localized weight gain. It is not clear whether or not the same type of feeding could be controlled by L/ D cycles which deviate grossly from a circadian or approximately 24-hr cycle.
The present study also indicated that in general, daily weights accurately reflect weights over a more extended period and that essentially the same average weight is maintained under continuous light and light dark cycles.
Circadian changes in feeding should be considered when food controlled behaviour obtained from various portions of a light cycle are compared, especially if some behaviour is obtained immediately before the dark cycle. This effect should also be considered in determining free feeding weights in that these weights vary substantially throughout a day. Weights could be determined early in the light cycle or the loft could be maintained on continuous illumination.
I gratefully acknowledge the assistance of Betty Palya for assisting in various aspects of the research.
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ZEIGLER, H. P., GREEN, H. L., and LEHRER, R. (l97l): Patterns of feeding behavior in the pigeon. J. comp. physiol. Psychol., 76: 468-477.
The effect of continuous illumination and a daily light dark cycle on the free feeding weights of pigeons was determined. Small unsystematic fluctuations occurred within each day during continuous illumination while substantial gains occurred immediately before the dark cycle. The daily accentuation in weight gain did not occur when a daily period without food was substituted for the period of darkness.
*)Dept. of Psychology, St. Joseph's College, Rensselaer, Indiana 47978, U.S.A.
Manuscript received 15 August 1975
Abstracting keywords: Photoperiodism, pigeon weight changes, weight fluctuations in pigeons.