亲缘关系与布氏田鼠双亲行为和杀婴行为关系的初探

根据幼仔发育的 5个阶段 :新生 (1～ 5日龄 )、耳立 (6～ 9日龄 )、睁眼 (10～14日龄 )、出巢 (15～ 2 0日龄 )和断奶 (2 1～2 4日龄 ) ,通过观察布氏田鼠对自己幼仔 (r=0 5 0 )和非亲缘幼仔 (r <0 12 5 )的行为反应 ,研究亲缘关系对布氏田鼠双亲和杀婴行为的影响。结果表明 :1)新生阶段 ,雄鼠抚育亲仔的时间显著多于非亲缘幼仔 ;断奶阶段 ,雄鼠与亲仔相触及在巢内活动的时间也显著多于非亲缘幼仔 ;雄鼠在耳立、出巢和断奶阶段嗅闻非亲缘幼仔 ,以及在新生和睁眼阶段修饰非亲缘幼仔的时间都显著多于亲仔。 2 )断奶阶段 ,雌鼠与亲仔相触的时间显著多于非亲缘幼仔 ,但在睁眼阶段修饰非亲缘幼仔 ,以及在新生、耳立和出巢阶段嗅闻非亲缘幼仔的时间显著多于亲仔。 3)雌雄鼠在15日龄前没有杀婴行为 ,15日龄后 ,开始对非亲缘幼仔发生杀婴行为 ;雌鼠杀婴行为受幼仔发育的显著影响 ,且杀婴频次显著高于雄鼠 ;雌鼠在断奶阶段对非亲缘幼仔的杀婴频次显著高于亲仔。综上所述 ,亲缘关系对布氏田鼠的双亲和杀婴行为有显著影响 ,这可能与个体间的已往经历 (熟悉性等 )或表现性匹配等辨别机制有关。     

棕色田鼠幼仔对双亲气味的行为反应

利用双向气味选择实验,观察了10日龄、14日龄、18日龄以及22日龄的棕色田鼠(Lasiopodomys mandarinus)幼仔对双亲底物和陌生鼠底物的行为反应,探讨了幼仔对双亲气味辨别的行为发育。10日龄的幼仔对双亲底物与陌生鼠底物没有显著偏好;14日龄和18日龄的幼仔对双亲底物的访问、嗅闻、滞留和挖掘行为均显著多于陌生鼠底物(P<0.05);22日龄的幼仔对双亲底物的嗅闻和挖掘行为显著多于陌生鼠底物(P<0.05),但对双亲底物与陌生鼠底物的访问和滞留没有显著性差异(P>0.05)。说明棕色田鼠幼仔在断乳前已完全能够辨别双亲气味和陌生气味,但随着日龄增加,22日龄的幼仔对陌生气味的偏好有上升趋势。     

雌性根田鼠断奶后对亲本尿气味的记忆

为研究亲子分开后雌性根田鼠对亲本气味的记忆持续时间，分别在未分开（20日龄）、分开10 d（30日龄）、20 d（40日龄）、30 d（50日龄）、40 d（60日龄）时，以新鲜尿作气味源，在行为观察箱中记录雌性根田鼠对不同气味源的行为响应模式，结果表明：(1) 未分开时，雌鼠遭遇父本气味时自我修饰的频次极显著高于陌生雄鼠气味，在分开10 d时，雌鼠接近父本气味的频次显著多于接近陌生雄鼠气味的频次，其对前者反标记显著少于后者；(2)分开20 d后，雌鼠对父本和陌生雄鼠气味的行为响应无明显差异；(3) 未分窝时，雌性根田鼠幼仔对母本和陌生雌鼠气味的行为响应无差异；（4）分开10—40 d时，雌性根田鼠对母本和陌生雌鼠气味表现出不同的行为响应模式。以上结果表明，在亲子分开10 d时，雌鼠仍能识别父本和陌生雄鼠的气味；分开20 d后，雌鼠不再能够识别父本和陌生雄鼠的气味；在亲子分开40 d时，雌鼠仍能识别母本和陌生雌鼠的气味。因此，雌鼠对父本气味的嗅觉记忆时间可以持续到亲子分开10—20 d之间；而对母本气味的嗅觉记忆时间则可以持续到亲子分开40 d以上。     

雌性根田鼠断奶后对亲本尿气味的记忆

为研究亲子分开后雌性根田鼠对亲本气味的记忆持续时间,分别在未分开(20日龄)、分开10d(30日龄)、20d(40日龄)、30d(50日龄)、40d(60日龄)时,以新鲜尿作气味源,在行为观察箱中记录雌性根田鼠对不同气味源的行为响应模式,结果表明(1)未分开时,雌鼠遭遇父本气味时自我修饰的频次极显著高于陌生雄鼠气味,在分开10d时,雌鼠接近父本气味的频次显著多于接近陌生雄鼠气味的频次,其对前者反标记显著少于后者;(2)分开20d后,雌鼠对父本和陌生雄鼠气味的行为响应无明显差异;(3)未分窝时,雌性根田鼠幼仔对母本和陌生雌鼠气味的行为响应无差异;(4)分开10—40d时,雌性根田鼠对母本和陌生雌鼠气味表现出不同的行为响应模式。以上结果表明,在亲子分开10d时,雌鼠仍能识别父本和陌生雄鼠的气味;分开20d后,雌鼠不再能够识别父本和陌生雄鼠的气味;在亲子分开40d时,雌鼠仍能识别母本和陌生雌鼠的气味。因此,雌鼠对父本气味的嗅觉记忆时间可以持续到亲子分开10—20d之间;而对母本气味的嗅觉记忆时间则可以持续到亲子分开40d以上。     

雌性布氏田鼠对雄鼠气味的辨别

通过雌性布氏田导其配偶和陌生雄鼠气味的辨别实验,以及无交配经历的成年雌鼠对社会等级不同的陌生雄鼠气的辨别实验发现,有生育经历的雌鼠对陌生雄鼠气味的探究行为明显多于对配偶气味的控究,但雌鼠在配偶雄鼠气味周围的停留时间、自身修饰行为和何处行为的发生频次和持续地陌生雄鼠,没有交配经历的雌鼠对处于从鼠地位的雄性个体气味探究行为多于对优势雄性的控究,而其他行为表现没有明显差异。表明,雌性布氏田鼠可以利用气味     

交叉抚育经历对根田鼠体重发育的影响

为检验交叉抚育经历对根田鼠体重发育的可能影响,监测了雌雄亲生和寄养幼仔的体重生长.结果发现: 在不同发育时期(2 ～ 70日龄),雄性亲生与寄养幼仔的体重没有差异; 除第18和20日龄外,其它时期(2 ～ 16,25 ～ 70日龄)雌性亲生与寄养幼仔的体重没有差异; 亲生和寄养幼仔在25日龄前两性体重差异不明显;25日龄后两性体重差异显著; 随着日龄的增加,根田鼠的体重日增长率呈现下降趋势.这些结果表明交叉抚育经历对雄性个体的发育没有影响,对雌性体重发育可能存在短暂影响,但持续时间不长(3 d ≤ T ＜ 9 d);根田鼠亲生和寄养幼仔体重生长的性别差异均在25日龄前后形成.     

布氏田鼠的择偶行为

在实验室通过布氏田鼠对配偶与陌生异性鼠,已交配「刚刚和别的雌（雄）鼠进行交配」和未效配异性鼠,熟悉和陌生异性鼠三种情况下配偶选择的实验研究。结果表明;雌性布氏田鼠对与配偶的造反地要多于陌生雄鼠;虽然对陌生和熟悉雄鼠选择差异不显著,但对陌生鼠的选择强度要高于熟悉雄鼠;同时对已交配和未交配雄鼠的选择地显著差异。     

哺乳期棕色田鼠对非亲缘幼仔的行为反应

通过观察产后2 日(L2)、6 日(L6)、10 日(L10)、14 日(L14)和20 日(L20)的棕色田鼠母鼠对2 日龄、6 日龄、10 日龄和14 日龄非亲缘幼仔的攻击行为和衔回行为,探讨了哺乳期棕色田鼠的母性行为与非亲缘幼仔的发育(日龄或个体大小)及母鼠产后时间的关系。结果表明,在哺乳前期(L2,L6),非亲缘幼仔的日龄大小显著影响母鼠的攻击行为(P < 0.05);在哺乳中期(L10,L14)及后期(L20),非亲缘幼仔的日龄对母鼠的攻击行为没有显著影响(P > 0. 05)。在整个哺乳期,母鼠对14 日龄非亲缘幼仔的攻击频次最高(P < 0.05)。产后不同时间的母鼠对同一日龄非亲缘幼仔的攻击频次没有显著差异(P > 0.05)。这些结果表明,哺乳期内的棕色田鼠对非亲缘幼仔的攻击与幼仔的发育有关,与母鼠的产后时间无关。     

雄性柴达木根田鼠断奶后对亲本尿气味的记忆

为了研究亲子分开后雄性柴达木根田鼠(Microtus limnophylus)对亲本尿气味的记忆持续时间,分别在未分开(20日龄),以及分开10d(30日龄)、20d(40日龄)、30d(50日龄)、40d(60日龄)时,以新鲜尿作为气味源,在行为观察箱中记录雄性柴达木根田鼠对不同气味源的行为响应模式.结果表明:(1)未分开时,雄鼠对父本气味的接近频次显著高于陌生雄鼠气味;分开10d时,雄鼠对父本气味的访问时间显著多于对陌生雄鼠气味的访问时间;分开20d时,雄鼠对陌生雄鼠气味的接近潜伏期极显著短于父本,对陌生雄鼠气味的访问时间极显著长于父本,其遭遇父鼠气味时的自我修饰频次显著少于陌生雄鼠气味.(2)分开30d后,雄鼠对父本和陌生雄鼠气味的行为响应没有明显差异.以上结果表明,在亲子分开20d时,雄鼠仍能识别父本与陌生雄鼠的气味;在分开30d后,雄鼠不再能够识别父本与陌生雄鼠的气味.(3)在未分窝时,雄性柴达木根田鼠幼仔对母本和陌生雌鼠气味的行为响应没有任何差异.(4)在分开10d时,雄性柴达木根田鼠对母本和陌生雌鼠气味表现出不同的行为响应模式;分开20～40d时,雄鼠对母本与陌生雌鼠气味的行为响应没有任何差异.以上结果表明,在亲子分开10d时,雄鼠仍能识别母本与陌生雌鼠的气味;在分开20d后,雄鼠不再能够识别母本与陌生雌鼠的气味.因此,雄鼠对父本气味的嗅觉记忆时间可以持续到亲子分开20～30d之间;其对母本气味的嗅觉记忆时间可以持续到亲子分开10d时.     

布氏田鼠雄性的优势地位

在实验条件下对雄性成年布氏田鼠（Microtus brandti）相遇后的优势地位及生理指标的研究结果表明：布氏田鼠雄性之间存在严格的等级关系;优势雄鼠生理指标中睾丸重量和血清睾酮激素含量高于从属雄鼠,而血清中皮质醇激素的含量低于从属雄鼠。优势雄鼠的探究、攻击和修饰等行为频次显著高于从属雄鼠,而从属雄鼠在跳跃频次上多于优势雄鼠。随着观察时间的延长,不论优势个体还是从属个体,其探究频次都呈现明显的下降趋势,其他行为的频次则没有显著差异。相关性检验说明,除攻击行为可以作为判断区分雄鼠等级的依据之外,修饰行为也可以作为判断的依据。     

Assessment of the sexual behavior of pregnant mares

Pregnant mares (N = 12) were observed with a stallion from early gestation until parturition for sexual behavior. Observations were conducted for 20 min per day for 5 days each month from September until July. No mares exhibited full estrus and no intromissions or ejaculations occurred at any time during the study. Social interactions such as male approach and female/female mutual grooming occurred with greater mean frequency or duration in some months of spring and fall than in winter months. (P less than 0.05). None of the recorded behaviors differed by month of gestation. In a comparison of the behavior of diestrous and pregnant mares in harem groups, no estrous behavior occurred and no differences in social interactions were found. Although progesterone may be sufficient to cause the absence of sexual behavior in diestrous mares, another estrous-inhibiting substance may be present during pregnancy at times of high estrogen and low progesterone.     

Grooming Circadian Rhythmicity,Progesterone Levels and Partner Preference of the Reproductive Pair of a Captive Common Marmoset (Callithrix jacchus) Family Group during Pregnancy and after Parturition

One family group of common marmosets (Callithrix jacchus) maintained in captivity under natural environmental conditions (Natal, Brazil, 05°46'S, 35°12'W) was observed by focal sampling at two non-consecutive days per week during two non-consecutive pregnancies (pregnancy 1: the last 8 fortnights before parturition; pregnancy 2: the last 5 ones) and after parturition (4 fortnights for both). The hourly percentiles of the duration of self-grooming and allogrooming interactions of the reproductive pair were submitted to Cosinor analysis for the 24-h period (p ≤ 0.05). The reproductive female's progesterone was monitored by fecal collection twice a week between 7:00 h to 9:00 h. Levels of progesterone were determined by ELISA method. During pregnancy 1, all interactions of the reproductive pair showed a 24-h statistically significant period. However, after parturition this periodicity is not present in some behaviors of the reproductive male. This animal presents the 24-h periodicity only toward to the reproductive female, the subadult son and to the newborns. Hormonal levels of the reproductive female showed isolated increases above 100 ng/g at the second and third fortnight after parturition, but did not characterize ovulation. Between pregnancy 1 and 2, the family was increased by the birth of four animals. During pregnancy 2, a statistically significant 24-h period was find only in self-grooming of the reproductive male and female, and in the interactions between the reproductive pair. Also, in the interactions of the reproductive male with only one of the juvenile son. After parturition the reproductive female ovulated at the second fortnight and became pregnant again. At this time, those interactions still have a 24-h period, except in grooming directed to the juvenile son by the reproductive male. As in the first post-partum, grooming directed to the newborns showed statistically significant 24-h period. These results suggest that the reproductive pair performs 24-h rhythmic grooming interactions only with some animals, supposed to be the preferential grooming partners. Furthermore, the temporal grooming expression in common marmosets may be affected by the reproductive condition (progesterone levels) of the reproductive female, by the care of newborn after parturition and the group size.     

Hormone profiles and nest-building behavior during the periparturient period in rabbit does

This study was done to elucidate the relationship between the hormones beta-estradiol, progesterone, prolactin and beta-endorphin and nest-building behavior in rabbit does during the periparturient period. Beta-estradiol increased as parturition approached with a significant increase starting 2 days before parturition (day -2). Progesterone decreased with the progress of gestation, but a significant decrease was observed starting on day -2. Prolactin concentration started to increase on day -2 prepartum but a significant increase in prolactin concentration was not noted until the last day of pregnancy. The concentration of beta-endorphin was highly variable during the sampling period and could not be correlated with the other hormones or nest-building behavior. To assess the role of prolactin in nest-building behavior, groups of rabbits were treated with bromocryptine, bromocryptine plus prolactin or saline (controls). Treatment with 4 mg bromocryptine or 4 mg bromocryptine + 1.5 mg bovine prolactin on days 25 and 27 of pregnancy did not affect the number of live kits born or the gestation length. The mean nest scores, a measure of the nest quality, were not affected by bromocryptine treatment, but treatment with bromocryptine plus prolactin resulted in lower nest scores (P < 0.05). Injection of 8 mg bromocryptine from day 28 of gestation to kindling resulted in an extended gestation (P < 0.05). Injection of 4 or 8 mg bromocryptine resulted in fewer live kits born (P < 0.05), reduced nest scores (P < 0.01) and blocked milk production, as determined from the palpable mammary tissue. These results indicate that prolactin has less influence on nest-building behavior than on milk production. The hormones most likely to influence nest building are beta-estradiol and progesterone because the levels of these hormones started to change at the time when the rabbits started to prepare nests. Further study is required to determine the influence of these hormones on nest-building behavior.     

半散放东北虎产仔行为的初步观察

1999年4月至2003年6月,采用随机取样法、扫描取样法和目标取样法对黑龙江东北虎林园半散放条件12只成年雌性东北虎的产仔行为进行观察。结果表明,半散放雌性东北虎的产仔行为可分为9种:站立、行走、躺卧、嗅闻、努责、梳理、生产、亲仔和舔食。雌性东北虎的躺卧和亲仔行为时间最长,分别为42.9% 和34.5% ;躺卧、努责和亲仔行为发生频率较高,分别为21.1%、16. 9% 和24.6%。单因素方差分析表明,不同雌性东北虎个体间躺卧、亲仔等行为有显著差异;不同年份雌性成年东北虎的站立、躺卧、梳理等产仔行为也具有显著差异。相关分析显示,躺卧行为与亲子行为(r_s= 0.602, P<0.05)、梳理行为(r_s=0.589,P<0.05)均呈负相关。     

Predicting time of parturition from changing vaginal temperature measured by data-logging apparatus in beef cows with twin fetuses

Vaginal temperatures (VT) of crossbred (Japanese Black crossed Holstein-Friesian) beef cows (n = 31) were measured by a data-logging apparatus to obtain serial data from days 0 to 6 before parturition. For both single and twin pregnancies, no significant differences were observed in VT during days 3-6 before parturition. Maternal VT was not affected by maternal weight just after parturition, parity, fetal sex, or total fetal litter weight. Average of twin litter weights for two males (MM) and two females (FF) had the strong positive correlations (r = 0.84; P < 0.05) with maternal VT, whereas twin weights of mixed-gender twins (FM) did not correlate with maternal VT (r = -0.26; P = 0.61). Maternal temperature decreased as weights of the female fetus of FM twins became heavier (r = -0.82; P < 0.05). In contrast, maternal VT of FF and MM twins increased as twin weights increased. We defined when the VT began to decrease before parturition by two different methods. One was the "same hours method" where differences in VT between a particular time of day and the corresponding time of the preceding day were compared when the VT was consistently > or =0.3 or > or =0.5 degrees C for more than 3h. The second method was the "maximum-minimum method" where decreased in the maximum or the minimum values of the day over > or =0.3 and > or =0.5 degrees C were compared to values of preceding day. Onset of decreased VT before expulsion was not different between singletons and twins. In an attempt to define the critical condition in predicting parturition, we estimated assumable predicting probability using the 31 cows that were collected VT. When the parturition occurred within 60 h in the "same hours method" and 72 h since VT was > or =0.3 degrees C and in the "maximum-minimum method", the assumable probability was 100%. In verification experiment under these condition, the "same hours method" had a higher probability of predicting the time of parturition than the "maximum-minimum method", and it was possible to detect the onset of decreased VT at the correct time by the minutes. We concluded that "same hours method" was useful for predicting parturition time in cattle with single and twin pregnancies by the serial measurement of vaginal temperature.     

Experimentally-elevated testosterone, female parental care, and reproductive success in a songbird, the Dark-eyed Junco (Junco hyemalis)

In male dark-eyed juncos (Junco hyemalis), experimentally elevated testosterone (T) decreases male parental care and offspring survival, but results in higher overall fitness through greater mating success. To help address the ensuing question of what prevents selection from favoring higher levels of T in male juncos, we manipulated T in female juncos. A previous study demonstrated no effect of experimentally elevated T on female incubation behavior, suggesting that female parental behavior might be insensitive to T. In this study we asked whether experimentally elevated T mediates other female parental behaviors and whether variation in T-mediated parental behavior might influence reproductive success. We videotaped free-living control- and T-females during nesting to quantify brooding behavior when young were 3 days old and provisioning behavior when young were 6 days old. Nest defense was measured by quantifying responses to a mounted predator placed near the nest. Reproductive success was assessed via fecundity, nestling quality, and nest survival. T-females spent less time than control females brooding but did not differ in provisioning rate. T-females performed fewer dives at the predator mount and, unlike controls, failed to increase defense as nesting progressed. T-females also had lower daily nest survival and lower nest success (odds of producing at least one fledgling). We conclude that some aspects of female parental behavior are sensitive to experimentally elevated T while others are not and consider the implications for the evolution of T-mediated characters in both sexes.     

Parental care in captive red-backed vole (Clethrionomys rutilus)

Parental behavior in ten pairs of male and female red-backed voles, Clethrionomus rutilus, was studied under laboratory conditions. Significant sex differences were found in total time spent in the nest, time spent by adults alone in the nest, grooming time, and nest-building activity; in half of the males under study, the level of paternal care was extremely low. These findings indicate different paternal contributions of female and male red-backed voles into the rearing of young, in agreement with the spatial-ethological structure of populations of this species. Parental behavior of C. rutilus is discussed in comparison with that of other species of the subfamily Microtinae.     

Positive correlation between the body weight of anestrous goats and their response to the male effect with sexually active bucks

In the present study, we analyzed the results of two years of response to the male effect in seasonally anestrous goats to investigate whether the activation of female reproductive activity by the male effect is related to the body weight of the females. Seventy-nine adult female Mexican mixed breed goats were used. The anestrous females were exposed during 15 days to sexually active males, and were classified into three categories according to their mean body weight +/-SD (42 +/- 9 kg) (Light: < or = 33 kg, n = 19; Medium: 34-50 kg, n = 46; Heavy: > or = 51 kg, n = 14). More than 98% of the goats from the Medium and Heavy groups showed at least one estrus behavior within the first 15 days following the introduction of the bucks, versus only 63% of the females from the Light group (P < 0.01). The interval between the introduction of the males and the onset of estrus behavior was longer in the females of the Light and Medium groups (4.2 +/- 0.8 and 3.3 +/- 0.3 days) than in the females of the Heavy group (2.0 +/- 0.2 days; P < 0.03). Also, body weight was negatively correlated with latency to first estrus (Spearman r = -0.57; P < 0.001). These results are in agreement with the hypothesis that the ability of anestrous goats to respond to the male effect is positively influenced by their body weight.     

Grooming Circadian Rhythmicity, Progesterone Levels and Partner Preference of the Reproductive Pair of a Captive Common Marmoset (Callithrix jacchus) Family Group during Pregnancy and after Parturition

One family group of common marmosets (Callithrix jacchus) maintained in captivity under natural environmental conditions (Natal, Brazil, 05°46'S, 35°12'W) was observed by focal sampling at two non-consecutive days per week during two non-consecutive pregnancies (pregnancy 1: the last 8 fortnights before parturition; pregnancy 2: the last 5 ones) and after parturition (4 fortnights for both). The hourly percentiles of the duration of self-grooming and allogrooming interactions of the reproductive pair were submitted to Cosinor analysis for the 24-h period (p ≤ 0.05). The reproductive female's progesterone was monitored by fecal collection twice a week between 7:00 h to 9:00 h. Levels of progesterone were determined by ELISA method. During pregnancy 1, all interactions of the reproductive pair showed a 24-h statistically significant period. However, after parturition this periodicity is not present in some behaviors of the reproductive male. This animal presents the 24-h periodicity only toward to the reproductive female, the subadult son and to the newborns. Hormonal levels of the reproductive female showed isolated increases above 100 ng/g at the second and third fortnight after parturition, but did not characterize ovulation. Between pregnancy 1 and 2, the family was increased by the birth of four animals. During pregnancy 2, a statistically significant 24-h period was find only in self-grooming of the reproductive male and female, and in the interactions between the reproductive pair. Also, in the interactions of the reproductive male with only one of the juvenile son. After parturition the reproductive female ovulated at the second fortnight and became pregnant again. At this time, those interactions still have a 24-h period, except in grooming directed to the juvenile son by the reproductive male. As in the first post-partum, grooming directed to the newborns showed statistically significant 24-h period. These results suggest that the reproductive pair performs 24-h rhythmic grooming interactions only with some animals, supposed to be the preferential grooming partners. Furthermore, the temporal grooming expression in common marmosets may be affected by the reproductive condition (progesterone levels) of the reproductive female, by the care of newborn after parturition and the group size.     

The effects of branches on prepartum nest building in gilts with access to straw

Sows farrowing in a semi-natural environment terminate nest building 1-7 h prior to parturition after having built a nest for which a variety of materials are used. No nest-building behaviour occurs during parturition and the sows remain lying in the nest throughout most of the farrowing. In contrast, many intensively housed sows are restless during farrowing. To investigate whether gilts housed indoors would use branches for nest building and whether access to branches would affect the termination of nest building and parturient behaviour, we studied gilts housed individually in pens designed to stimulate natural nest building. The control group (n=21) had unlimited access to straw and the experimental group (n=21) had unlimited access to straw and branches. During nest building all the gilts used straw and all the experimental gilts also used branches. In the experimental group the interval from termination of nest building to birth of the first piglet (BFP) was significantly longer than in the control group (132 versus 58 min, P=0.04). In the experimental group, nest-building behaviour was also performed by fewer individuals during the interval from BFP until 2 h after than in the control group (38% versus 71% of the gilts, P=0.03). Gilts that performed nest building during this interval carried out more postural changes (P<0.001) and spent less time in lateral recumbency (P=0.001) than gilts which did not perform nest building. On average, gilts that performed nest building behaviour after BFP (n=26) spent 54% of the first 2 h of parturition in lateral recumbency and carried out 16 postural changes. Gilts that did not perform nest building behaviour during this interval (n=16) spent 85% of the time in lateral recumbency and carried out five postural changes. In 10 gilts that were selected randomly from the experimental group nest building was studied in more detail. In these gilts nest building peaked between 17 and 6 h prepartum. There was no difference in amount of behaviour directed towards straw and amount of behaviour directed towards branches.The results indicate that the termination of nest building in sows is under environmental feedback control. When only straw was provided the nests did not have much of a lasting structure. However, when gilts had access to straw and branches more structured and functional nests could be built. These nests may have been more effective in reducing the motivation for nest building prior to the onset of parturition.