Behavioral Reactions to Gustatory Stimuli in Young Chicks (Gallus gallus domesticus) JUDITH R. GANCHROW JACOB E. STEINER ATIDA BARTANA The Hebrew University Jerusalem, Israel

Freely-moving, posthatch chicks were individually presented 2 concentrations each of quinine, citric acid, fructose, sucrose, sodium saccharin, and distilled water and their behavioral reactions were videotaped and analyzed. Already during the first posthatch day distinct rejection responses to quinine and citric acid could be recognized. Prolonged head shaking and beak clapping episodes were the most dominant features of these reactions. While responses to water and sweet stimuli could be interpreted as acceptance behaviors, the resolution was generally not fine enough to discriminate between reactions to the 2 different sweet concentrations of these stimuli or between them and water. When only water or sugar solutions were presented to other hatchlings in a single session, there was a suggestion of more definite acceptance behavior to some sweet stimuli as compared to water. It is concluded that the systems mediating aversive gustatory responses are present and functioning in posthatching chicks while acceptance responses, though present, are less discriminative among stimuli.

The functional maturation of gustation in mammals is an ongoing process corresponding to parallel developmental events in taste buds and their afferent neural relays (e.g., Hill, 1987a, b; Hill, 1988; Hosley & Oakley, 1987; Lasiter & Kachele, 1988; Miller & Smith, 1988; Mistretta, Gurkan, & Bradley, 1988; Nagai, Mistretta, & Bradley, 1988; Vigorito & Sclafani, 1988). Relatively little attention has been given to similar events in avian species. It is known that the trunk ganglia mediating gustation in the chicken seventh, ninth, and tenth nerves contain postmitotic neurons by the fifth day of incubation (D’Amico-Martel, 1982) and incipient distal and proximal ganglionic processes have already appeared (e.g., Tello, 1923; van Campenhout, 1937). By the eighth embryonic day the tongue is easily recognizable as a lingual structure, salivary glands have begun to form, and swallowing is initiated over the ensuing 4 to 5 embryonic days (i.e., E8-E13), Reprint requests should be sent to Dr. J. Ganchrow, Department of Oral Biology, The Hebrew University-Hadassah Faculty of Dental Medicine, P.O. Box 1172, Jerusalem 91010, Israel. Received for publication 20 July 1989 Revised for publication 5 December 1989 Accepted at Wiley 31 January 1990 Developmental Psychobiology 23(2): 103-1 17 (1990) 0 1990 by John Wiley & Sons, Inc.

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Hamilton, 1952; Romanoff, 1960). Taste buds supplied by the chorda tympani nerve (Ganchrow, Ganchrow, & Oppenheimer, 1986) in the region of the anterior mandibular glands are first recognized only on embryonic day 17 (E17) with the first signs of taste pores commencing at E l 9 (Ganchrow & Ganchrow, 1987). SedlaCek (1962) has reported that a conditioned reflex, using saccharin as the unconditioned stimulus for swallowing, can be established on E17, although it is not clear that taste is the critical feature mediating this behavior. Chicks hatch on the twenty-first day of incubation and behavioral responses to gustatory stimulation have been observed in embryos during the last day before hatching (Vince, 1977). Interestingly, no significant effects of taste were reported when NaC1, HC1, glucose, and sucrose-octa-acetate were dissolved in distilled water and compared to distilled water alone. Water by itself induced significant behavioral responses, and only when taste substances (HCl, fructose, NaCI, KCl, and quinine) were dissolved in egg fluids did a clear pattern of responding emerge. While the gustatory system is apparently functional at this perihatching stage, the hypersensitivity to water may be a uniquely embryonic feature: Adult chickens do display differential oro-facial reactions to sucrose, sodium chloride, acetic acid, and quinine solutions as compared to water (Gentle, 1978, 1981, 1982; Gentle & Dewar, 1981; Gentle & Harkin, 1979). However, Gentle (1982), reviewing data gathered using just 3 response measures (exaggerated beak and tongue movements, headshaking, and beak wiping) defining the “aversion response” (Gentle, 1975), noted that differences between stimuli often were reflected quantitatively rather than qualitatively since water, too, could elicit all those components under their conditions for observation. In neither the embryonic nor the adult chickens were clear qualitative differences in behavioral reactions between the various taste stimuli reported. The present investigation examined behavioral responses to taste stimuli in freely moving chicks recently emerged from the egg environment, prior to any water drinking experience. Previous studies employed restraint and/or manual insertion of fluids directly into the mouths (e.g., Gentle, 1978, 1981, 1982; Vince, 1977), which conceivably could have interfered with subtle behavioral features associated with and discriminating between the various stimuli. Drinking was spontaneous in the present experiment. Behavioral reactions were videotaped for later analysis, a procedure that has proven extremely valuable in interpreting taste reactions in a variety of species (crustaceans (Steiner & Harpaz, 1987); rats (e.g., Grill & Norgren, 1978); hamsters (Brining, Belecky, & Smith, 1989); nonhuman primates (Steiner & Glaser, 1984); and humans (e.g., Ganchrow, Steiner, & Daher, 1983; Rosenstein & Oster, 1988; Steiner, 1987; 1988).

Experiment 1 Methods

Subjects and Recording Procedures Thirty-one Anak (white broiler breed) chicks were obtained from the Kibbutz Tzuba Hatchery during the first hours after hatching and tested the same morning prior to any drinking experience. Video recording (JVC-VHS, S-9, color video

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system) of the freely moving chicks took place in a heated room (about 26-27°C) with a booster portable electric convection heater placed adjacent to the 45 x 45 cm behavioral stage. Two 100 W lamps illuminated the stage in addition to natural lighting from a window. A 20 x 30 cm mirror was placed behind the stage affording the chick a reflective view of another chick and expediting subsequent behavioral scoring by making both sides of the chick visible. About 70 ml of taste solutions or distilled water were presented one at a time in numerically precoded glass petri dishes (9 cm inside diameter) placed near the center of the stage. During stimulus presentation and subsequent behavioral scoring no information concerning the nature of the taste stimulus was available to the observers. Chicks were tested one at a time in batches of 6, 6, 9, and 10, each batch on a different day. Behaviors were videotaped from the time of stimulus presentation and continued for the first 60 seconds after the stimulus was first sampled. Real time was displayed on the monitor and recorded simultaneously with the behavioral sequence. To facilitate exact timing measurements, an additional digital stopwatch (millisecond accuracy) was activated when the first stimulus sampling occurred. The time between stimulus presentations was about 2 min and the whole testing sequence was about 30 min per chick. Spontaneous fluid sampling occurred about 75% of the time. Chicks not spontaneously sampling within 3-5 min of stimulus presentation were gently prodded to establish contact. If this failed to elicit sampling, that stimulus trial was aborted. In 3 cases spontaneous drinking never occurred, and these animals were eliminated from further analyses.

Test Solutions Each chick received a different random sequence of distilled water, 0.3 and 1.7 M fructose, 0.005 and 0.2 M sodium saccharin, 0.001 and 0.02 M quinine hydrochloride, and 0.01 and 0.1 N citric acid. Choice of stimuli was based on a comparison of those substances found to be effective in chicken studies on taste reactivity (e.g., Gentle & Harkin, 1979;Vince, 1977),taste preference (e.g., Engelmann, 1937b; Kare, Black, & Allison, 1957), and taste electrophysiology (e.g., Gentle, 1984; Kadono, Okado, & Ohno, 1966). Chemicals were of reagent grade and double distilled water was a stimulus and the solvent. An additional exposure to distilled water preceded each stimulus series to familiarize the chick with the drinking situation. These introductory trials were not used in the data analysis.

Behavioral Scoring Procedures Behavioral reactions were measured by reviewing the videotapes and tallying specific response components initiated by each fluid contact on separate scoring grids for each stimulus. Slow motion or frame-by-frame analysis was utilized when closer examination of detail was required. Behavioral features selected for scoring were based on analyses of behavioral responses of group-tested chicks in a pilot experiment (Bartana, 1988). Features selected included pecking contact (beak touching the surface of the liquid stimulus), drinking contact (pecking contact initiating oral motor reactions), beak clapping (beak cyclically opening and closing), gaping (beak sustained in a wide open position), beak wiping (rotational head movements bringing alternate sides of the beak in contact with the stimulus dish,

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stage, or the animal’s foot), head shaking (rapid side-to-side movements of the head), walking away from or reapproaching the dish, vocalizations, and pecking at the floor. These features included and expanded upon reaction components reported for mature and embryonic chickens (Gentle, 1982; Vince, 1977). The intensity and hedonic values of the overall behavioral response to each stimulus presentation were scored on 2 separate 100 mm visual analogue scales where the left extreme represented no response, or as unpleasant as imaginable, while the extreme right end of the line indicated the maximal possible response magnitude, or maximum positive response, respectively. Data were then tabulated according to event frequency per stimulus trial (minute) or event frequency per drinking contact as well as percentages of animals displaying each behavioral event. Responses to each stimulus were compared with those to water and other taste stimuli using a t-test for repeated measures with a .05 rejection level.

Results

Hedonic and Intensity Estimates The mean hedonic estimates ranged between 12 and 48 (Figure la) on the 100 mm scale. The lowest mean estimates (“unpleasant”) were associated with the higher (0.02 M) quinine (12.5 +- 2.6) and (0.1 M) citric acid (1 1.5 t 2.7) concentrations and these were significantly different from estimates for water (42.1 7.5) (t(20;19) = 4.88;6.06, respectively, p < .005) and the 4 sweet stimuli (t’s(16-21) = 4.15-6.06; p < .005). Likewise, responses to the lower concentrations of quinine (28.2 ? 5.5) and citric acid (37.6 k 8.0) were judged to be more pleasant than those to the higher concentrations (t(21;18) = 3.84;4.47, respectively, p < .005), and responses to 0.001 M quinine were interpreted as still less pleasant than those to ~ .025). The mean hedonic estimates forfructose, saccharin, water (r(20) = 2 . 0 9 , < and water were remarkably similar. The mean intensity estimate (Figure lb) for the response to water was 43.2 -+ 7.7 and the other estimates clustered around this value (range of mean intensity estimates for all stimuli = 37-56). Only the estimate for 0.02 M quinine (56.1 +9.9) approached significance when compared to water (t(20) = 1.67; p = 0.057). Within stimulus types, only intensity estimates between the 2 concentrations of quinine (0.001 M QHCl = 38.9 t 6.4) obtained significance (t(2l) = 2.38; p = .OlS).

*

Behavioral Features The percentage of animals expressing component behavioral features in response to the various taste stimuli is compared in Figure 2. Responses to the higher and lower concentrations of each stimulus are respectively displayed in the top and bottom rows. Percentage responses to water are exhibited in the center of each row for comparison. The selected behaviors appeared to be stimulus-related and are arranged in a descending order, based on percentage of animals responding when 0.02 M quinine was the stimulus. These behaviors included head shaking ( s ) , prolonged beak clapping (cl), walking away (w), pecking contact (p), beak

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wiping (b), repeated drinking contacts (c), and gaping (g). It may be seen that the higher concentrations of quinine and citric acid produce similar behavioral response profiles, which are different from those to water, fructose, and sodium saccharin. Expressed as coefficients of correlation (Spearman rank, Siegel, 1956), response profiles between 0.02 M quinine and either 0.1 N citric acid or 0.001 M quinine correlated at r = 0.96 and 0.86, respectively. Response profile correlations of 0.02 M quinine with other stimuli never exceeded r = .43. Response profiles for all other stimuli correlated fairly well with that to water (r = 0.79-1.0). Quantitative representation of 2 of the oral behaviors that could be related to stimulus aversion are to be found in Table 1. In comparison to water, fructose, or saccharin, there was a significant decrease in number of drinking contacts per minute when quinine or the higher concentration of citric acid was the stimulus (t(16-22) = 1.99-5.12). Since overall there was more stimulus sampling to water, fructose, and saccharin, there averaged more beak claps per minute (range = 60-75 claps/minute) as compared to quinine and the higher citric acid concentration (range = 45-55 clapdminute). However, when average number of beak claps per contact were considered, the more concentrated quinine and citric acid stimuli elicited a significantly more vigorous response than did water (t(19,20) = 2.67, 4.13) (see Table I) or the other stimuli (means ranged from 18.8 5 3.1 (water) to 22.3 -+ 3.7 (0.001 M quinine); t(16-22) = 1.89-4.14); p < .005-.04) with the exception of the 0.02 M quinine comparison to 0.3 M fructose (22.1 5 4.2; t(18)

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Table 1 Mean Number of Oral Behaviors to Gustatory Stimuli as Compared t o Water (Standard Errors of the Means in Parentheses). Drinking Contacts/Min Water Quinine 0.001 M 0.02

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18.8 (23.1)

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3.4 (20.7) 1.6 (50.3)**

20.2 (“3.5) 37.5 (56.4)**

4.2 (*0.8) 4.3 (20.8)

22.1 (24.2) 22.1 (23.5)

3.7 (20.5) 3.9 (50.8)

20.1 (k2.5) 18.8 (23.9)

Citric Acid 0.01 0.1 Fructose 0.3 1.7 Saccharin 0.005 0.02

* p < .01 ** p < ,005 = 1.38;p = .09). When beak clapping was maintained over 1 full second, the rate was around 6-8 hz, regardless of stimulus type. Headshaking was another prominent feature that could be interpreted as an aversive response to quinine and citric acid (see Fig. 2), but was also present for almost half of the animals sampling water, fructose, and saccharin. There appeared to be 2 qualitatively different forms of head shakes: quick, i.e., one of very short duration (100-200 msec); and strong, i.e., >200 msec, of various durations. The incidence of these 2 types of head shakes is illustrated in Figure 3. The total number of quick head shaking episodes to each of the stimuli for 22 presentations of all stimuli is represented by the open bars. It may be seen that there is a baseline quick headshaking response of around 10-20 to all of the stimuli. To these are added strong head shakes (filled bars) which were primarily elicited by the higher concentrations of citric acid and quinine, somewhat by 0.001 M quinine and minimally by the remainder of the stimuli. Nonaversive stimuli are likely to elicit about 1 head shake per animal with about 20% of these low-incidence shakes described as “strong.” However, if the stimulus is quinine or 0.1 M citric acid, the total number of head shakes increases to around 2-4 per animal with up to 90% of these described as “strong.” While beak wiping, gaping, and walking away all tended to be primarily associated with quinine and citric acid, the variability across animals in displaying such behaviors precluded including these reactions as consistent features of the aversion response. The average incidence of beak wiping was about 1 per minute for 0.02 M quinine and 0.1 M citric acid as compared to averages of about 0.2 wipes/min for the sweet stimuli and 0.4 wipes/min for water. None of the comparisons were significantly different from water. Relatively few chicks exhibited the gaping response (n = 13). For these animals, gaping frequently averaged around 0.3 gapes/min for 0.02 M quinine and

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0.01 and 0.1 M citric acid, whereas water never elicited a gape. The remaining stimuli elicited a rate of about 0.1 gapes/min except 0.02 M saccharin which produced 0.4 gapes/min. Likewise, there were overlapping variances in the walking away response, although there was a tendency to do so at a slightly higher rate to quinine or 0.1 M citric acid (range of means = 0.65-0.68 walks away/min) as opposed to the other fluid stimuli (range of means = 0.43-0.59 walks away/min).

Discussion This experiment suggests that the gustatory system of hatchling chicks adequately mediates discrimination of quinine and citric acid from water, fructose, and saccharin solutions when water is the solvent. Hedonic and intensity estimates, percentage of animals responding, and incidence of specific component behavioral features all support an emerging pattern of aversive responding consisting of vigorous beak clapping, head shaking, few drinking contacts and occasional gapes, beak wipes, and retreats associated with quinine and citric acid. Gentle and Dewar ( I 98 1 ) also observed prolonged beak clapping associated with higher concentrations of quinine (0. I M) and acetic acid (2.0 M) as compared to water during the first posthatch day; responses to sweet stimuli were not tested. Furthermore, results from the present experiment suggested a graded increase in response incidence and intensity with increasing quinine concentrations relative to water at this age.

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Experiment 2 Previous studies in both full-term chick embryos (Vince, 1977) and adult chickens (e.g., Gentle & Harkin, 1979) reported differential behavioral reactions between a neutral environmental stimulus (egg fluid or distilled water) and fructose, dissolved in egg fluids or water, respectively, in the concentration range employed in the present study. Since stimuli were presented in a random order in Experiment 1, possibly lingering sour or bitter stimuli intraorally may have masked natural responses to fructose, water, and saccharin, making it difficult to discern differences between them. Furthermore, in Experiment 1, the opportunity to sample test stimuli for 10 full minutes may have superimposed a growing satiety effect onto the behavioral responses. It has been reported that satiated animals are more likely to react with features of aversion, even to sugar solutions (Grill, 1978). Experiment 2 was undertaken to clarify this issue by presenting only 4 sweet stimuli and water. Sucrose replaced saccharin in Experiment 2, since saccharin most resembled water in the measures sampled in Experiment 1 , and since Gentle’s (1978) taste reactivity data suggest that adult chickens can discriminate sucrose from water. In preference tests, saccharin, in concentrations of 0.001-0.01 M, is least preferred or moderately rejected compared to the natural sugars in both young and mature chickens (Engelmann, 1934, 1937a,b; Kare et al., 1957; Jacobs & Scott, 1957).

Methods Eight hatchling chicks were obtained from the same hatchery, and tested and scored under conditions identical to those in Experiment 1. Each chick received a different random sequence of 0.3 and 1 M sucrose, 0.5 and 1.2 M fructose, and 2 samples of double-distilled water for 1 min each, bringing total maximum consumption time down to 6 min. The duration of the testing session was about 20 minlchick.

Results

Hedonic and Intensity Estimates

*

The mean hedonic estimate for water was 34 7 while the average estimates for concentrations of both sugars ranged between 40 and 60. Only 1 .O M sucrose and 0.5 M fructose induced overt reactions judged to be significantly more pleasant than those produced by water (Mean = 55.2 2 7.3 and 60 % 3.6; t(8,8) = 2.03, 3.44; p < .05 and .005, respectively). The response intensity for water was judged to be 29 3.5, while judgments for concentrations of the 4 sugars ranged from 34-52. However, only 1 .O M sucrose and 0.5 M fructose were judged as significantly more intense when compared to water (means = 51.8 t 6.4 and 50.6 k 2.4; t(8,8) = 2.3 and 5.8; p < .05 and .005, respectively). Examination of component response features under the conditions of Experiment 2 revealed that the sugars elicited more drinking contacts than did water. The average number of drinking contacts to water was 2.6 k 0.5 per minute, while

*

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*

the range for the other stimuli was between 4.2 0.5 and 4.9 k 0.8. All sweet substances except 0.3 M sucrose produced significantly more drinking contacts than did water (t(8,8,8) = 2.1, 3.2 and 2 . 1 ; ~< .05, .01, and .05 for 1.0 M sucrose, 0.5 M and 1.2 M fructose, respectively). No significant differences occurred between any pairs of sugar solutions. Beak clapping was an index in Experiment 1 whose duration seemed to increase with aversion. In the present experiment, this behavior averaged 37 3.6 claps/contact to water while the sugars elicited from 27 2 3.2 (0.5 M fructose) to 34 2 6.7 (0.3 M sucrose) claps/contact. Water elicited significantly more beak claps/contact than either 1.0 M sucrose (t(8) = 2.4, p = .02) or 0.5 M fructose ( t ( 8 ) = 2.2, p = .03). No differences were observed between sugar types or concentrations on this measure. The quick head shake was observed in 38% of the animals for water and 25-50% for the set of sugar solutions. In contrast, strong headshaking was rarely observed: one animal exhibited this behavior in response to water and sucrose. The total number of head'shakes (strong plus quick) per animal for these 5 stimuli averaged 1 head shake per presentation as in Experiment 1. Beak wiping was not observed to any stimulus. Only 1 animal exhibited a gape during the presentation of 1.2 M fructose and water and these stimuli appeared first and second in the series order. Likewise, walking away was rarely observed, with 0 to 0.25 retreats per animal recorded to any of the sugar stimuli and 0.38 retreats per animal to water. Seventy percent of such responding occurred during the last 2 stimulus presentations of the series.

*

Discussion Results of Experiment 2 indicate that hatchling chicks are capable of distinguishing between water and sugar solutions as measured by their overt behavioral responses. Each of the sugars elicited more drinking contacts and fewer beak claps per contact than did water. In parallel, higher hedonic and intensity estimates independently were assigned to the sugars than to water. Interestingly, the method did not generally discriminate response differences between sugar types or concentrations, although there was a tendency for the higher concentration of sucrose to produce a larger response than 0.3 M sucrose. However, the relation was reversed for the 2 fructose concentrations. In Experiment 2 the sugars and water were equally unlikely to elicit aversive (gaping, prolonged head shaking, etc.) behaviors, although the response to water was consistently assigned hedonic values on the less pleasant half of the hedonic scale (i.e., 6 0 ) as had occurred in Experiment 1. When nested among citric acid and quinine stimuli (Experiment I), water was judged slightly less hedonically negative than in Experiment 2. Behavioral reactivity to water in chick embryos has previously been reported to be quite vigorous (Vince, 1977) and less intense in adults, but with behavioral components suggesting aversion (e.g., Gentle, 1982). In addition, water elicits an electrophysiological response above background in the chicken glossopharyngeal (Halpern, 1962; Kitchell, Strom, & Zotterman, 1959) and chorda tympani (Gentle, 1983, 1984) nerves, as well as in the geniculate ganglion (Gentle, 1987). Perhaps water hypersensitivity in embryos diminishes somewhat as a function of posthatch age as the gustatory system adapts to its new

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local environment devoid of embryonic fluids. Parallel developmental changes in salt sensitivity may contribute to this phenomenon if the chick gustatory system matures in a manner similar to that in lambs and rats (see Hill, 1987a). It would be interesting to know whether sugar dissolved in physiological saline and tested against saline might unmask a clearer sweet response.

General Discussion The results of these experiments demonstrate that in the first posthatching day, chicks are capable of discriminating some concentrations of quinine, citric acid, sucrose, and fructose from water, when water is also the solvent. Furthermore, the behavior pattern defining the adult reaction to these stimuli is already established at this early posthatch time, and some embryonic features are maintained as well.

The Behavioral Response to Aversive Stimuli Component features of hatchling chick reactions to quinine and citric acid resembled those obtained in adult and embryonic chickens, and 2 characteristics (head turning and gaping) are components of aversive reactions defined in mammals (e.g., Berridge, Flynn, Schulkin, & Grill, 1984; Ganchrow, Oppenheimer, & Steiner, 1979; Ganchrow, Steiner & Canetto, 1986; Ganchrow et al., 1983). The aversion response in chickens is best characterized by prolonged, repetitive mandibulatory movements (beak clapping), head shaking, and sometimes beak wiping or gaping (e.g., Gentle, 1978, 1981, 1982, Gibbs, 1982; Vince, 1977). Each of these behaviors has the potential of actively or passively removing offensive fluids from the oral cavity. Sustained beak movements and head shaking perhaps best define the reaction to bitter and sour stimuli in the present as well as previous studies. Of the remaining 2 features, gaping was more noticeable in embryos (Vince, 1977) and beak wiping among adults (e.g., Gentle, 1981).When confined to the shell, the prehatching embryo may not easily emit the beak wiping response. Gaping was rarely observed among adults at gustatory stimulation levels comparable to those employed here, and was mainly observed with extremely intense gustatory or other noxious chemical stimulation (Gentle, personal communication). In both embryos and hatchlings, the tendency to gape varied considerably among animals. Still, the average rates were somewhat similar: comparing Vince’s (1977) results to the present data (in gapes/chick/min), water elicited 0.1 and 0; and quinine-0.1 (0.014 M QHCl) versus 0.1 and .3 (0.001 and 0.02 M QHCl); acid-between 0.3 and 0.4 for 0.3 M HCl, and 0.01 and 0.1 M citric acid, for embryos and chicks, respectively. Historically, there has been disagreement as to the significance of head shaking behavior in birds during consumption of taste solutions: Rensch and Neunzig (1925) argued that head shaking signified aversion, while Engelmann (1934) concluded that it was more related to tactile sensitivity of the mucosal epithelium associated with the nasopalatal opening. Both observers were probably correct. Systematic analysis of the videotaped records obtained in the present experiments suggested that there were 2 functionally different forms of head shaking behavior associated with drinking: one, a response to aversive taste stimuli; and the second,

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temporally shorter one, capable of induction by any fluid stimulus. Kuenzel(l983) has described the sequence of behaviors resulting in drinking as the immersion of the beak into the fluid allowing the lower bill to fill, and then upward head movement allowing water to flow from the mouth to the esophogeal opening via gravity. The upper beak oral epithelium is interrupted by an elongate nasopalatal opening (see, e.g., Berkhoudt, 1985; Ganchrow & Ganchrow, 1985). Perhaps while elevating the head for drinking, droplets lodge in this opening, producing tactile stimulation and inducing the quick shake to remove them. This could explain the presence, albeit at low incidence, of a baseline of quick head shakes to all stimulus types. T h e Behavioral Response To Sweet Stimuli In adult chickens, increasing the concentration of fructose or sucrose increases the frequency of beak movements, head shakes, and beak wipes within limits (Gentle & Harkin 1979). In hatchlings, prolonged head shaking and beak wiping were rarely associated with the sweet stimuli or water. This difference may be developmental, since likewise in chicke embryos, no significant differences were found in the head shaking category when sugar was compared to the neutral stimulus (Vince, 1977). Furthermore, embryos were most likely to gape to 0.28 M fructose (.45 gapes/embryo/min) while hatchlings did so at a much lower rate f.05 and .IS gapes/embryo/min for 0.3 and 1.5 M fructose, respectively). However, procedural differences cannot be ruled out when comparing the present study to earlier ones. For instance, different modes of orally infusing stimulus solutions used in previous experiments may have biased the likelihood for a particular response pattern; likewise, the difference between a quick and a strong head shake may be much less noticeable without videotape analyses. Whether chickens taste, or prefer, sugars and artificial sweeteners has long been somewhat controversial and comparisons between studies are often difficult due to methodological differences including short- versus long-term tests, deprivation level, strain, and age factors. Results of Experiment 2 suggest that the hatchling chicks detect and show a mild preference for some concentrations of sucrose and fructose as indicated by their more frequent sampling of these stimuli compared to water. Utilizing 2-bottle preference techniques, Jacobs and Scott (1957)reported that 1- to 42-day-old chicks have only a slight and inconsistent preference for 12% (0.3 M) sucrose, which becomes more pronounced after 43 days. Likewise, still older chickens have been reported to exhibit moderate-to-strong preferences for sucrose, fructose, glucose, and maltose (Barbato, Siege], & Cherry, 1982; Engelmann, 1937a; Kare, Black, & Allison, 1957; Rensch & Neunzig, 1925). However, Kare and Medway (1959) reported that 1-18-day chicks were, at best, indifferent to fructose and sucrose in the 0.07-0.7 M range, and 14-week-old chickens were reported to significantly reject 1.7 M fructose and 0.9 M sucrose (Gentle, 1972). It is noteworthy that in Experiment 2, 1.2 M fructose was judged less hedonically positive than 0.5 M fructose and had more aversive behavior components attached to it, suggesting a possible decreasing palatability for the higher fructose concentrations. It is possible that chickens of all ages detect natural sugar solutions, but do not express an immediate strong preference [strain differences notwithstanding (e.g., see Barbato et al., 1982; Kare & Maller, 1967)l. Kare & Ficken, (1963), and

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Kare and Maller (1967) suggest that positive postingestional consequences, e.g., making up a caloric deficit, may be critical for expression of a sugar preference, as recent work in the starling appears to confirm (Schuler, 1983). Engelmann (1934) also reported that sugar preferences seemed to develop only if sugar and water were regularly presented together. Perhaps the very mild preference and relatively low level of taste reactivity seen in chicks during the posthatch period gets amplified in adulthood only as a consequence of previous experience with this substance. Alternatively, perhaps there is some critical change in the posthatching physiological development of taste buds andhervous system altering the perception of sugar stimuli. In mammals, maturational changes continue to affect gustatory responding well after adultlike bud structural features appear (see Hill, 1987a for review). In conclusion, newly hatched chicks have a functioning gustatory system allowing them to reject aversive and to detect sweet-tasting stimuli. Since avian drinking behavior incorporates several gross, coordinated head and beak movements, and possibly due to the lack of a strong sweet preference, the difference in the observable reaction to sweets compared to water is small in contrast to the vigorous difference when quinine or citric acid is the stimulus.

Note This research was supported by Grant 3226/84 from the United States-Israel Binational Science Foundation (BSF), Jerusalem, Israel. We would like to thank Eyal Bartana for programming the statistical analyses, Ilana Frank for technical assistance, Don Ganchrow for helpful comments on an earlier draft, Thomas Geiselman for assistance in data processing, and Kibbutz Tzuba for supplying the chicks. A preliminary report of these findings was presented at the IX International Symposium on Olfaction and Taste, Snowmass, Colorado.

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