ACTA NEUROBIOL. EXP. 1977, 37: 99-115 THE EFFECT OF STIMULI EMITTED BY SUCKLINGS ON TACTILE CONTACT OF THE BITCHES WITH SUCKLINGS AND ON NUMBER OF LICKING ACTS P. KORDA and J. BREWINSKA Department of Neurophysiology, Nencki Institute of Experimental Biology Warsaw, Poland Abstract. Bitches changed abruptly their maternal behavior on 15th and 16th day of the maternal cycle, following an exchange - on the beginning of 15th day - of some puppies from their own litter for other 2-3 days old puppies. The total time of tactile contact with puppies on days 15 and 16 greatly increased as compared with the 13th and 14th day, i.e., the days immediately preceding the exchange of puppies. The number of licking acts also increased. In control bitches, whcse puppies were not exchanged, the indices of maternal behavior showed no increase on days 15 and 16, compared with days 13 and 14 of the maternal cycle. The foster 2-3 days old puppies were also a source of much stronger stimuli releasing care-giving reactions than the own, correspondingly older puppies. INTRODUCTION In homoiothermic animals induction of a natural parental behavior towards the offspring, as well as its qualitative and quantitative changes taking place in the subsequent phases of the maternal cycle, are controlled in two ways. On the one hand, they are regulated by endo- and exogenous factors whose efectiveness results from their summation and temporal cumulation. The group of past and temporally summating exogenous factors, or, rather, exteroceptive stimuli will be called past cumulative stimuli (PCS). On the other hand, the parental behavior and its
temporal fluctuations are evoked or provoked by the currently and directly acting exteroceptive stimuli (current exteroceptive stimuli - CES). Among PCS the following factors may be distinguished: seasonal changes in daylight and climate, dietary variations and intraspecific factors acting upon the parents' senses during past phases of the current reproductive cycle. It should be added here that PCS act frequently, though not always. through the mediation of the relevant chains of hormonal reactions. In turn, nest- or offspring-defending reaction which immediately follows danger signals or evokes a strong anxiety in the mother or father may be a good example of the CES. The importance and strength of the PCS or CES effects on parental behavior probably differ in various species and in relation to various forms of that behavior. They also happen to vary with the lapse of time and according to the rule of double quantification (9). As known, the parental behavior of the homoiothermic animals undergoes evident phasic changes. They occur as the time passes and they are adjusted to the current state of the psychophysical development of the litter. The question arises - what causal factors and mechanisms are indispensable for the adjustment of the parents to the current, constantly changing requirements of the maturing offspring. With regard to investigation of factors and mechanisms which control the course of phasic changes in the parental behavior of the mammals, we could not find in literature a descfiption of experiments carried out on animals phylogenetically higher than Lagomorpha or Rodentia (rodents). Neither are there any such materials available on Carnivora (carnivores). The only relevant reference to the subject, though without experimental documentation, was made by Menzel and Menzel (10). They noticed that currently weakened manifestations of maternal care were intensified anew to a maximum when, in the middle of lactation period, all the puppies of a bitch were taken away and substituted by alien, newborn ones. However, due to lack of any description of material and methods as well as the course of the experiment, no detailed interpretation of the observed phenomenon can be formulated. The course of normal phasic changes taking place in the care-giving behavior of mother-bitches was described by Rheingold (13). She carried out observations on five pure-bred bitches whose behavior was recorded four times a day during 15-min sessions. It was found that, over the whole cycle of maternal behavior of the bitches 1, its vigor decreased rapidly from the day of delivery as the time passed. In our investigations we aimed at studying the mechanisms controll- -- I The cycle of maternal behavior is meant as a chronological succession of behavioral phenomena in the mother from the day of birth till the offspring becomes physically independent.
ing phasic changes in the maternal care of carnivores. The role of sucklings as a source of CES eliciting respective phasic changes in the mpternal behavior of the bitches seemed especially interesting. Our second, th'ough very important, goal was to ve~ify on our material some of Rheingold's (13) results (concerning natural course of behavioral changes) and supplement them with more detailed data. MATERIAL AND METHODS The method of investigation applied in this study required the use of pairs of mothers currently in a suitable period of maternal cycle. In each pair there was a mother-bitch whose own pups were substituted by those of the donors. It was necessary for this experiment to get 1-3 day old sucklings in order to use them as substitutes for the 15 days old puppies of the experimental mothers. As it proved difficult to obtain foster puppies of suitable age, we had to reduce the number of subjects. Nevertheless we tried to get from our bitches precise and representabive data concerning particular days of the maternal cycle. We therefore adopted a strict regime of 14 h of uninterrupted observation on always the same predetermined days of the cycle. Mongrel bitches were used as a material more representative for the species of Canis familiaris than any pure-bred animals. Eight randomly chosen bitches were used together with their litters. Five bitches bred four pups each, in the remaining mothers the number of the pups was, after delivery, also reduced to four. Seven additional, randomly chosen 1-3 days old sucklings were used in the experiment. Those sucklings were born of alien bitches, unconnected with these investigations. Four of the eight bitches (bitches 5-8) with their litters formed an experimental group, whereas the remaining four (bitches 1-4) with their offspring were treated as a control group. In our experimental conditions the control bitches represented normal mothering behavior not influenced by the study itself and served as reference for the evaluation of the behavior of the experimental bitches. The basic element of our method was the substitution of puppies. The experimental bitches were deprived of two, or, exceptionally, one of their own puppies when they were 15 days old, and then they were given two (or exceptionally one) sucklings 1-3 days old for the next 2 days of the experiment. The exchange was carried out on the 15th day counting from the day of birth and 20-30 min prior to the beginning of observation for that day. In the experimental bitches 5, 6 and 7 two of their own puppies were substituted by two alien ones - 12-13 days younger than their own. In bitch 8 only one puppy was substituted by another, 14 days younger than her own. The exchange of puppies always
took place when the bitch was absent from the nest and in such a way that the alien puppies were in the nest for at least 15-20 min before she was brought back. No substitution took place in the control bitches. As already mentioned, the selected manifestations of maternal behavior in the control and experimental bitches were registered non-stop for 14 h a day on the 2nd, 3rd and 4th day and on the 13th, 14th, 15th and 16th day after delivery. Two elements of maternal behavior were recorded during the observations: (i) amount of time spent by the bitch in direct tactile contact with the puppies (which was almost tantamount to the global time spent by the bitch in the nest) and (ii) number of acts of licking the puppies by the bitch. Neither the number of pups with which the mother remained in tactile contact nor the kind of contact were taken into account. Only the mutual tactile contact between the bitch and her offspring was important. The lack of thermoregulating reactions in the newborn sucklings made them dependent on the heat acjuired through tactile contact with the mother's body. On the other hand, a rapid development of thermoregulating reactions in the sucklings made them soon independent of body contact with their mother, leading to a rapid disappearance of the necessity of constant contact with the mother. That is why we expected prompt and clear phasic changes in the intensity of maternal behavior with the lapse of time. When licking acts were recorded, the number of puppies licked during one act was not considered. Intervals in licking lasting less than 30 s were not taken into account either; e.g., two successive licking acts interrupted by such a short pause were treated as one act. Such pauses were not frequent and if they occurred, they were as a rule filled with smelling and nosing of the next puppies prior to licking any of them. The length of the pauses was measured with a stop-watch. All observed litters were born between April and October. The bitches and their offspring were kept in an ordinary room with a door leading to a lawn. There was neither air-conditioning nor acoustic isolation. Room temperature (18-23OC) was maintained with the exception of the 13th day of observation of bitch 8, when temperature dropped to 15'C. Before the expected delivery the bitches were familiarized with this room several times and from delivery on they remained there all the time until the end of the 16th day of the maternal cycle. A low wooden box with a cardboard floor served as a nest. The door leading to the lawn was usually slightly open, giving the bitches freedom to stay where they chose. The observer stayed in the same room about 1-1.5 m from the nest and behaved passively towards the bitch. If the door was shut because of cold and the bitch left the nest wanting to get out, observer opened the door and did not close it until the bitch returned.
RESULTS Phasic changes of the undisturbed maternal behavior Intervention in the experimental group of bitches did not begin unit1 early in the morning on the 15th day of their maternal cycle. Therefore the behavior,of both groups of bitches (bitches 1-8) on the 2nd through 4th and 13th >hrough 14th day was undisturbed and natural. Moreover, the number of puppies remaining with their mothers in both groups and the environmental conditions were identical. For that reason the data concerning all the eight bitches can be used to evaluate natural phasic changes until the 14th day of the studied samples of the maternal cycle. The chronology of changes in the level of undisturbed maternal behavior was strikingly similar in all eight studied females. The amount of time spent by the bitches on tactile contact with their pups during the first 2 days after birth was very large and the dispersion of individual differences was very small (Fig. 1 and 2). On the 2nd day, during 14 h daily observations the amount of that time considerably exceeded 13 h in seven bitches and only fell slightly below that limit in one bitch (bitch 2) on the 2nd day. Indices for the 13th and 14th day of the cycle dropped remarkably in all examined bitches. Compared to the indices for the 2nd and 3rd day (looo/o) in individual bitches they only amounted to about 30 /o, ranging: 25 to 35"Io in 6 bitches (bitches 1-6) and to about 56@/0 in the remaining 2 (bitches 7 and 8). That marked drop in the second decade of the maternal cycle is consistent with the tendency of phasic changes described by Rheingold (13). Chronology of changes in the number of licking acts which took place in an undisturbed cycle of maternal behavior was alike (Fig. 3 and 4). The number of licking acts in control and experimental bitches (bitches 1-8) was far smaller on the 13th and 14th day of the cycle than during its 2nd and 3rd day. Although there were individual differences in absolute values, a marked drop in the number of licking acts was observed on the 13th and 14th day in all eight bitches, with indices ranging individually from 27O/o to 54Vo. Both manifestations of maternal behavior of the control bitches observed during the 13th and 14th day were maintained at a low level over the next 2 days of the cycle (i.e., 15th and 16th), which suggests that they reflected natural, undisturbed course of maternal behavior. Therefore the results obtained during the 15th and 16th day of the cycle in experimental bitches should be estimated also by comparing them with the results of those bitches recorded on the 13th and 14th day of the cycle - independently of the direct comparison of both groups of bitches.
CONTROL ANIMALS Fig. 1. Total time of tactile contact of bitches with puppies during 14-h sessions on selected days of the maternal cycle in control animals. The data for the 2nd and 3rd da'y of the maternal cycle are presented in block I (diagonal lines), for the 13th and 14th day in block I1 (vertical lines) and for the 15th and 16th day in block 111 (crossed lines). The data for the 4th day of cycle (plain bars) are presented additionally to described fully the maternal activity during the first days after delivery. The last diagram presents mean data. Immediately below the abscisae the relative values are expressed in per cent. The total mean results for the 2nd and 3rd day of the cycle of all four bitches in the given group were taken as 100 /o.
EXPERMENTAL AN/MALS 14 14 8 '2 8 ro * 8-6 6 Q 4 8 2 2 Successive days of maferni& 2 4 Q Fig. 2. Total time of tactile contact of bitches with puppies during 14-h sessions on selected days of maternal cycle in experimental animals (shown in the same way as in Fig. 1). Numerals in circles show the number of puppies exchanged prior to observation on the 15th day of the cycle, marked with a thick vertical line.
Such arrangement of the observations permits to recognize that the changes in the course of maternal behavior are due to the exchange of puppies. Tactile contact of the bitch with the puppies Figures 1 and 2 show the absolute, individually measured amount of time spent in daily tactile contacts with the pups by the control and experimental bitches respectively. The last graphs in both Figures represent the mean data. In order to evaluate the results it is necessary to make the following comparisons in the behavior of experimental bitches: (Fig. 2): 1. The data for the 15th and 16th day with those for the immediately preceding 2 days (13th and 14th); 2. The data obtained during the 15th and 16th day with those for the 2nd, 3rd and 4th day of the cycle; 3. The results of the experimental bitches (Fig. 2, bitches 5-8) with the corresponding results of the controls (Fig. 1, bitches 1-4); 4. Mean results of the control and experimental groups (Fig. 1 and 2) with special reference to the 15th and 16th day. The comparable quantitative data are presented in three 2-day, graphically differentiated blocks (Fig. 1 and 2). The data for the 4th day served to supplement the description of maternal behavior during the first days of the cycle, and they have not been included in the blocks. It permits a comparison of results in all three blocks also in absolute values. A global duration of observation for each 2-day block amounted to 28 h (1680 min), i.e., the total time of observations in two consecutive daily sessions, 14 h each. Mean data in block I show that during 28 h of observation the duration of tactile contact of the control bitches with the pups (Fig. 1) amounted on the average to 26 h 57 min. The respective diagrams show that the individual variations are very slight (Fig. 1). In the second 2-day block (block 11) the individual and average duration of contact in the control bitches dropped to about 113. The mean time equalled 8 h 23 min (503 min). This amounts to merely 31 /o of the mean data for block I (treated as 100 /o). In turn, it should be pointed out that the indices for block I11 in the control bitches are very similar to the indices for block I1 and hence differ markedly from the indices for block I. Figure 2 shows that in the eqerimental bitches the mean duration of contact with puppies in block I was almost identical with that of the control bitches and amounted to 26 h 56 min. Individual differences in that' period of the maternal cycle were very small. In the experimental
bitches those was a considerable decrease in both individual and mean duration of contact in block 11. Mean data for the latter amount to 42O/o of the data for block I. On the other hand, in block 111 (following the exchange of pups) the results of the experimental bitches differed considerably from the corresponding results of the control bitches. Both individual and average results of the former increased more than twice. Mean duration of contact of the experimental bitches with the pups in block 111 equalled 21 h 26 min (1286 min) - twice as long as in block I1 - which was equivalent to 80 /o of the duration of contact in block I. In block I11 the relevant value for the controls was only 31 /o. It can be easily seen from the diagrams that in the individual experimental bitches the trend of behavioral changes was alike. It should be stressed that the change in behavior of the experimental bitches took place right after the substitution of the puppies. In the control bitches the difference in total duration of tactile contact between blocks I1 and 111,' as analyzed by Student-Gosset t-test, was statistically considerably below of the level of significance (t = 0.104; Po,,, = 2.45). In the experimental group of bitches these differences (Po,,,) were statistically significant. Puppy licking The absolute numbers of puppy licking acts are presented individually in Fig. 3 (control bitches) and Fig. 4 (experimental bitches). The last graphs in both Figures represent the mean data. In order to evaluate the data on the basis of these diagrams it is necessary to compare the same results and positions as were described previously in the discussion of Fig. 1 and 2. The comparable quantitative data are presented in three 24ay, graphically differentiated blocks. The results for the 4th consecutive day of the cycle have not been included in the blocks. The data compiled in each block comparised the results of two consecutive daily sessions of observation within the cycle (similarly to Fig. 1 and 2). As shown in Fig. 3, the mgan number of licking acts in the control bitches equalled 129 in block I, only 45 in block I1 and 39 in block 111. Taking the mean number of licking acts in block I as maximal for the control bitches and treating it as 100 /o, the relative number of licking acts in block I1 averaged only 35O/0 and in block 111-30 /o. In the experimental bitches (Fig. 4) the mean number of licking acts in block I amounted to 95. In block 11, as in the control bitches, a very considerable individual decrease was observed, the mean number of acts being 46. In block 111, on the other hand, i.e., after the puppy
exchange - the mean number of licking acts, as opposed to the controls, increased in the experimental bitches to 108. In two bitches (7 and 8) the number of licking acts actually outnumbered the indices for block I. 120? roo B.$ 80 s 60 ' 40 & 3 20 s CONTROL AN/MALS Bitch 2-1 120 Mean data Fig. 3. Total number of puppy-licking acts during 14-h sessions on selected days of the maternal cycle in the control animals. Data are presented in the same way as in previous Figures.
EXPERIMENTAL AN/MALS Successive d ~ of p m~terniq '. I Mean '20 data Fig. 4. Total number of puppy-licking acts during 14-h sessions on selected days of the maternal cycle in experimental animals (shown in the same way as in Fig. 3). Numerals in circles show the number of puppies exchanged prior to observation on the 15th day of the cycle, marked with a thick vertical line.
In comparison to the mean number of licks in block I which - as in the control group - we accepted as a maximum for the experimental bitches (1000/o), the mean indices for block I1 dropped in the experimental bitches by half, while in block I11 they exceeded the indices for the first days of the cycle, reaching 113O/o. The diagrams show that the trend of the data obtained in individual bitches was similar. In the control bitches the difference in the number of licking acts between blocks I1 and 111, as analysed by Student-Gosset t-test, was statistically considerably below of the level of significance (t = 0.63; Po,o; = 2.45). In the experimental group these differences were statistically significant. The increase in frequency of puppy-licking in the experimental bitches directly followed the substitution of older pups by younger ones, as was the case with the duration of tactile contact. Additional observations Apart: from the results presented in Fig. 1-4, other observations have also been made. In two litters it was found that the day after the exchange of puppies two older ones remaining with their own mother revealed symptoms of anxiety and insomnia. These were manifested by loud vocalization and crawling about the nest for tens of minutes. In the meantime the substituted newborn pups calmly sucked the bitch. However, the older puppies quietened down immediately when the observer manually evoked in them the urinating reflex. The amount of urine excreted during a single provoked urination seemed very large. Interestingly enough, both bitches paid little attention to "alarm" vocalization of the older pups when the younger ones were in the nest. In order to explain this fact the following test was carried out on three bitches on the second or third day after the substitution of the puppies. When the bitches left the room on their own (to urinate on the lawn nearby) the observer pressed the puppy's leg till vocalization appeared in response to pain. If the sound came from one of the substituted sucklings 3-4 days old at that time - the bitches responded very vigorously and immediately hurried back to the nest. One bitch even interrupted urination on hearing this signal. If, on the other hand, the complaint came from her own puppies, then 16-17 days old - the bitch's reaction was weak, delayed by tens of seconds or more and without any sign of hurry in returning to the nest. A similar test was performed on the 4th bitch which was.taken out to the adjacent room, 9 m from the nest. Following the vocalization of her own 17 day old pups, the bitch trotted back to the nest within 14 s, whereas she galloped back in 7 s after hearing the vocalization of the younger pups.
DISCUSSION In Lehrman's (8) investigations it was shown that the previous even passive, participation of Ring Dove males in nest-building and hatching is a sine qua non condition for the appearance of both their subsequent interest in the nestlings and other parental behaviors and that it is indispensable for the initiation of food production in their crops. Lehrman also found that the blood prolactin (LTH) level was markedly lowered in the males who did not participate in nest-building or hatching. It suggests that the past cumulative stimuli (PCS), as they were called earlier, can initiate appropriate endogenous chain reactions (mostly hormonal), which, in turn, are accompanied by an appropriate urge to parental behavior. It seems plausible that PCS also condition the selective reactivity of the parent animals CNS and facilitate their care-giving behavior. By merely enabling the Ring Dove male to see the hatching female for an adequate number of days - his sequent parental behavior and food production in the crop can be induced. Terkel and Rosenblatt (15) as well as Noirot (12) claim that the preexposure of virgin females of mice and rats to a 5-12 day's close contact with live sucklings of their species sufficed for some kinds of maternal behavior to appear. The above cited investigations (8, 12, 15) are a good illustration of the influence of intraspecific PCS-type interactions on parental behavior. The intraspecific influences indispensable for the induction of parental behavior in nonparents is called sensitization. It must be emphasized that PCS need not always evoke hormonal reactions, nor act through their mediation. Rosenblatt (14) succeeded to evoke some manifestations of parental behavior in hypophysectomized and/or ovariectomized rats by means of a sufficiently long sensitization period. Thus PCS do not always act via the so far known hormonal system, nevertheless the way they act must be different from the mechanizm of action of the stimuli referred to above as CES. When the latter are emitted by baby animals and act upon the senses of their own or adoptive parents, an adequate care-giving behavior is evoked or released immediately. In a normal course of motherhood the period of parental sensitization becomes probably needless. It may be illustrated by an immediate defense reaction of the parents, following the stimuli signalling danger to the offspring. Similarly, the retrieving behavior, typical for a normal course of maternity, is a direct (usually prompt) mother's reaction to the baby's falling out of the nest. However, the effectiveness of the action of CES may in the care-giving behavior depend on the earlier action of PCS. The latter may be a requisite of an adequate receptivity of the parents to CES. Interaction of both groups of factors in the control of parental beha- 4 - Acta Neurobiologiae Experimentalis
vior was examined in Gastrostelus aculeatus fish (3). It was also observed by Grota (1) in laboratory rodents. Grota's interesting findings suggest that intensification of maternal behavior in mother-rats resulted from: (i) the number of days from the female's delivery day, (ii) actual number of youngsters in her nest, and (iii) the age of the young currently in the nest. The two last points should be included in CES. The report on the Symposium in Washington in 1972 presented by Herrenkohl and Sachs (2) also confirms the important effect of CES on the manifestations of maternal behavior in rodents. However, these reports have been based mainly on the behavior of mothers who were completely deprived of one of their analyzers after a surgery or chemical lesion. The essential role of the effect of CES on the induction of epirneletic (care-giving) vomiting as a manifestation of parental behavior in Canidae has been determined in the studies of Korda (4, 5). However, in male dogs the effectiveness of CES seemed to depend on the earlier period of their sensitization through exposure to the intraspecific exteroceptive stimuli that represented PCS. Our results authorise the conclusion that phasic changes in the natural course of maternal behavior of the bitches are controlled chiefly by the stimuli emitted by the puppies. It appeared that these changes depend above all on the pup's stage of development and only in a small degree - on the physiological state of the mother-bitch. This was reported in our earlier communications (7). Successive, chronological changes taking place after pregnancy, delivery, onset of lactation and with the passage of days of the reproductive and maternal cycle seemed to have only a very limited effect on the intensification of maternal behavior. Contrariwise, the pups' substitution strongly influenced the bitch's behavior. It means that the endo- and exogenous factors of the PCS-type had relatively little effect on the course of phasic changes in the maternal behavior. If that had not been the case, the behavior of the experimental bitches (who were under the influence only of stimuli emitted by their own puppies for the initial 14 days of the cycle) would have been adjusted irreversibly to the development stage of their own puppies. And yet it appeared that such behavior was reversible and evidently depended on the substituted, younger pups. Prompt behavioral changes of the bitches following closely the exchange of some of their own offspring for younger puppies, points to the role of CES as the main factor controlling the phasic changes in maternal behavior. Moreover, our results allow us to conclude that under described conditions the puppies at the age of 1-3 days, even alien ones, are a much stronger source of sign-stimuli for the mother-bitches 15-1 6 days after delivery than their own 12-14 days older pups. The exchange of only
one puppy to the bitch 8 is a good proof of this conclusion, which is also supported by additional observations concerning behavioral reaction of the bitches to "alarm" vocalization of the younger and older pups. The use of such terms as "alien puppy" or "own puppy'' is probably unjustified. The cited observations provide no basis for concluding that in the investigated period of maternity the bitches discerned between their "own" and "alien" pups at all. When appropriate steps were taken to make the substituted puppies smell of the adoptive mother's nest - the orienting response of the bitch to the presence of foster pups was very weak or unnoticeable. These terms have primarily been used to facilitate the description of the observed phenomena. We exchanged only some of the bitch's own pups for younger ones (7) and not the whole litter, as was the case in rodents (1, 12). By leaving with the bitch some of her own puppies along with foster pups, we theoretically created conditions for two types of behavior in the female. She could have behaved according to the chronological phase of her motherhood, i.e., in agreement with her own puppies' age or, on the contrary, inconsistently with chronology but in accordance with the age of foster pups. Finally, she might have acted in an intermediate way or manifested behavioral disorganization. Therefore the evident change in the experimental bitches' behavior, with a tendency to regress to earlier phases of maternity, permitted an unequivocal interpretation of the phenomenon as resulting from the presence of the foster pups. Our data support such interpretation, which seems biologically justified. In natural conditions the offspring of carnivores is usually composed of sucklings very similar as to the level of development. However, in some litters the position of the feti in the uterus and the succession of the deliveries can lead to quite considerable differences in the development level of the young (delivery in bitches may last over 10 h) (11). In the case of different levels of development of the feti, possible changes in the intensity and mode of mothering would - due to exteroception - be directed toward an especially active care of the weaker or more poorly developed sucklings, which would give them better chances of survival and a compensation for delayed development in the fetal period. However, observations made by breeders indicate that it seldom is directed to sick or deficient puppies. Probably the stimuli emitted by them do not correspond to the sign (key) stimuli, to which the mother- -bitch responds with care-giving behavior. In such a case other types of behavior appear that should also be ranked among maternal but not care-giving behaviors. It can be defined as behavior aiming at the elimination of sick or anatomically deficient sucklings. Strangely enough, the indices for bith 8 on the 13th day are ratcher
atypical in comparison to all remaining results. They differ both from individual and average indices for all other bitches (bitches 1-8) on that day (Fig. 1-4). It refers both to the prolonged tactile contact of bitch 8 with her pups and to the number of licks. On the 13th day of the cycle the reactions of the experimental bitches were still undisturbed by the experimental intervention. It seems therefore that the behavior of bith 8 on the 13th day was indeed atypical. Probably it was due to a drop in temperature which occured that day in the nestling room. Unexpected and not fully explained is the size of increase of number of licking acts after the substitution of puppies' in bitches 7 and 8 (see Fig. 4). The number of licks considerably exceeded that observed in the bitches on the first post-delivery days. There is an alternative explanation of this observation. Frequent licking may be due to the abundance of milk at this lactation phase and supranormal milk consumption by the substituted sucklings, and also to a small capacity of their bladders and the ensueing need to urinate more frequently. Still another reason might as well be an excessive milk consumption by own, older puppies. They took the advantage of a markedly prolonged presence of the bitch in the nest which, in turn, resulted from the presence of the substituted sucklings. Therefore the older pups could suck over a much longer period of time and that is why they needed to urinate more often. Finally, it is probable that after the younger sucklings had been brought to the bitch she limited the time of licking of older pups and, instead, adjusted herself to the needs and capacity of the bladders of the substituted, younger puppies. In this way the licking-act time might have become "standard", i.e., equal for all pups in the nest regardless of their age, but at the same time insufficient to empty the bladders of the older puppies. Thus the bitches might have licked the older pups more frequently, but for a shorter period of time. On the basis of additional observations (see above), the last explanation seems plausible. This investigation was supported by Project 10.4.1.01 of the Polish Academy of Sciences. The excellent technical assistance of Mrs Elibieta Maciulewicz is greatly appreciated. REFERENCES 1. GROTA, L. J. 1973. Effects of litter size, age of young and partity of foster mother behavior in Rattus novegicus. Anim. Behav. 21: 78-103. 2. HERRENKOHL, L. R. and SACHS, B. D. 1972. Meeting report: Sensory regulation of maternal behavior in mammals. Physiol. Behav. 9: 689-692. 3. Van IERSEL, J. 1935. An analysis of the parental behavior of the three-spined stickleback. Behaviour, Suppl. 3.
4. KORDA, P. 1972. Epimeletic vomiting in female dogs during the rearing process of their puppies. Acta Neurobiol. Exp. 32: 733-747. 5. KORDA, P. 1974. Epimeletic (care-giving) vomiting in dogs: a study of the determinating factors. Acta Neurobiol. Exp. 34: 277-300. 6. KORDA, P. and BREWIRSKA, J. 1975. Studies on the course and regulatory mechanisms of maternal behavior in female dogs: 1. Physical contact of the mother to puppies and her licking behavior. Proc. XI11 Congr. Pol. Physiol. Assoc. (Gdansk), p. 173. 7. KORDA, P. and BREWIRSKA, J. 1975. Studies on the course and regulatory mechanisms of maternal behavior in female dogs: 2. Process of feeding by suckling. Proc. XIII. Congr. Pol. Physiol. Assoc. (Gdansk), p. 174. 8. LEHRMAN, D. S. 1964. The reproductive behavior of ring doves. Sci. Am. 211: 48-54. 9. LORENZ, K. 1950. The comparative method in studying innate behavior patterns. Symp. Soc. Exp. Biol. (Cambridge), p. 221-268. 10. MENZEL, R. and MENZEL R. 1953. Einiges aus der Pflegewelt der Mutterhiindin. Behaviour 5: 289-304. 11. NAAKTGEBOREN, C. 1971. Die Geburt bei Haushunden und Wildhunden. A. Ziemsen, Wiltenberg. 103 p. 12. NOIROT, E. 1972. The onset of maternal behavior in rats, hamsters behavior and mice. A. Selective review. In Advances in the study of behavior. Vol. 4. Acad. Press, New York, p. 107-145. 13. RHEINGOLD, H. R. 1963. Maternal behavior in the dog. In H. R. Rheingold (ed.). Maternal behavior in mammals. Nat. Inst. Ment. Health, New York, p. 169-202. 14. ROSENBLATT, J. S. 1967 Nonhormonal basis of maternal behavior in the rat. Science 378: 1512-1514. 15. TERKEL, J. and ROSENBLATT, J. S. 1972. Quoted Noirot (12). Accepted 16 December 1976 Piotr KORDA and Janina BREWINSKA, Nencki Institute of Experimental Biology, Pasteura 3, 02-093 Warsaw, Poland.