Nest-building Activity Research Articles

Neonatal exposure to chlorpyrifos affects maternal responses and maternal aggression of female mice in adulthood

CD-1 mice were exposed to the organophosphate pesticide chlorpyrifos (CPF) throughout postnatal days (PND) 11–14 at the subtoxic dose of 3 mg/kg. At adolescent age, females and males underwent a sociability test in which level of sociability and social preference were measured. At adulthood only females' behavior was analyzed. Maternal behavior of CPF-exposed females was assessed on postpartum day 1 after removal of the pups for 1 h, while anxiety levels were measured in a 5 min dark–light test on postpartum day 2. Nest defense response to an unfamiliar male intruder was assessed on postpartum day 7. In addition, from birth to postpartum day 7 a detailed analysis of nest building activity was carried out. Neonatal CPF exposure does not interfere with social behavior and social preferences at adolescence, whereas at adulthood it induces significant behavioral alterations in lactating females. Motivation to build and defend the nest was decreased in CPF females that were also less anxious than controls in the dark–light paradigm. These results confirm that developmental exposure to CPF induces long-lasting alterations in selected sexual-dimorphic responses of the adult social repertoire, and suggest that early exposure to CPF might interfere with hypothalamic neuroendocrine mechanisms regulating social responses.

Aberrant nest building and prolactin secretion in vitamin D receptor mutant mice

1α,25(OH) 2D 3, the hormonal form of vitamin D, is a neuroactive seco-steroid hormone with multiple functions in the brain. Most of these effects are mediated through the nuclear vitamin D receptor (VDR), widely distributed in the central nervous system. Our earlier studies showed that mutant mice lacking functional VDR have specific behavioural abnormalities, including anxiety and aberrant maternal behaviour, which may be hormonally regulated. Here we describe impaired nest building behaviour in VDR mutant mice. Since prolactin plays a key role in the regulation of nest building in both sexes, we also examine whether VDR mutant mice have altered prolactin levels. Overall, serum prolactin levels were increased in VDR mutant mice, accompanied by marked impairments in their nest building activity. In contrast, there were no differences in prolactin mRNA expression levels between wildtype control mice and VDR mutant mice. Collectively, these data suggest that partial genetic ablation of VDR affects prolactin system in mice, and that altered serum prolactin levels in VDR mutants may underlie some of their behavioural abnormalities, such as impaired nest building.

Temporal changes in demand for and supply of nests in red bishops (Euplectes orix): dynamics of a biological market

The red bishop (Euplectes orix) is a highly polygynous and colonial weaverbird. Males construct several nests within their territories to which they try to attract females, and females are solely responsible for incubation and raising offspring. In this paper, we describe the characteristics of the red bishop’s mating system as a biological market and investigate the role of nests built by males as a traded commodity in a mating market. As timing of breeding in red bishops in arid and semi-arid zones depends on rainfall patterns which are often unpredictable, there are temporal changes in demand for and supply of nests within a breeding season, with breeding activities of males and females being highly synchronised. We found that males increased their nest-building speed with increased female breeding activity independently of rainfall, indicating that supply follows demand in this mating market. The supply of nests was always larger than the demand for nests. Construction costs for nests increased with demand for nests as indicated by shorter nest-building duration and shorter building delays between two consecutively built nests at times of high breeding activity. Males as a trading class are chosen according to the age of their nests offered, with young nests having a higher probability of being accepted by females. Furthermore, female choosiness with regard to nest age decreased when their own market value decreased, as predicted by biological market theory. The temporal changes of breeding activity together with the female preference for young and fresh nests require that males quickly adjust nest-building activity to varying female demand for new nests. However, males with a better adjustment of building speed to female breeding activity did not gain higher mating success.

Early piglet mortality in loose-housed sows related to sow and piglet behaviour and to the progress of parturition

The aim of the present study was to identify characteristics of sow behaviour and parturition related to early piglet mortality in loose-housed farrowing sows. Data from 152 farrowings that originated from three different herds with loose-housed sows during parturition were used. Graphical chain models were used to model the relationships between perinatal behaviour, periparturient individual conditions (time of day of parturition, rectal temperature 1–3 days postpartum) and causes of early piglet mortality. Modelling was based on the correlation between variables within herd and farrowing batch. The analysis showed that different causes of mortality were linked to different behavioural variables during the periparturient period and that they grouped into three independent categories. The first category was associated with stillbirth and death due to other causes. Stillbirth was positively related to the variation of the inter-birth interval and negatively related to the percentage of piglets that suckled during the first 8 h after birth of first piglet (BFP). Death due to other causes was negatively related to the suckling activity during the post-partal period (9–24 h after BFP). The second category was associated with piglet crushing, which was positively related to much lateral lying the last 4 h before BFP. Finally, the third category was associated with death due to lack of colostrums ingestion of colostrum, which was linked to the time of parturition and sow rectal temperature on days 1 and 2 after farrowing. Sows that gave birth during the morning compared to evening/night had more dead piglets due to lack of colostrums ingestion. Death due to lack of colostrums ingestion was also higher in sows with high rectal temperature on the day after BFP. The results further showed that litter size not only influenced mortality but also behavioural variables. High litter size was related to high nest building activity before BFP, low but more variable inter-birth intervals, and much lateral lying after BFP. The study points towards several areas of interest for further research that can help understand early piglet mortality. These include causes of variation in the progress of parturition, causes of individual differences in sow activity and responsiveness to piglets, and early management of farrowing. In addition, the study suggests possible indicators of problematic farrowings rendering liveborn piglets at risk. These include prepartum lateral lying in the sow, low suckling activity and rate of stillbirth.

Parental care and sexual interactions in Mongolian gerbils (Meriones unguiculatus) during the postpartum estrus

The behavior of male and female Mongolian gerbils was continuously video-recorded from 24 h before the parturition to the end of postpartum estrus. We noted that the mean interval between the delivery of the last pup and the first mounting was 13 h and 32 min. Over the whole duration of the postpartum estrus (7 h and 41+/-57 min), females spent significantly more time in crouching over, pup licking, nest building and "digging" activities, and were more recipient of allogrooming than males. Maternal pup retrievals were not very frequent (14.0+/-5.6 episodes), but males never retrieved pups nor exhibited a full sequence of nest building activity. Males spent a longer mean time in bodily interactions with females, as compared to the time they spent with pups, and engaged in intense copulatory activity (592.8+/-40.5 mounts or 1 episode per 46.7s); even during the delivery process males attempted to force copulation, but females rejected mounting in all cases. We conclude that females exhibited higher levels of parental care than males, and our findings suggest that males compete with pups in attracting the female's attention, since they actively disrupt maternal care or persistently persecute the female in order to copulate.

Biologia de nidificação e aspectos ecológicos de Anthodioctes lunatus (Smith) (Hymenoptera: Megachilidae, Anthidiini) em área de tabuleiro nordestino, PB

A biologia da nidificação de Anthodioctes lunatus (Smith) é descrita e registrada a ocorrência da espécie no Nordeste do Brasil. Os ninhos foram coletados na Reserva Biológica Guaribas, PB, no período de maio/2000 a maio/2002, utilizando ninhos-armadilha durante um estudo de abelhas e vespas que nidificam em cavidades preexistentes. Os ninhos de A. lunatus foram coletados em vegetação savânica típica de tabuleiros costeiros nos meses de dezembro/2001 e janeiro/2002. Foram coletados 10 ninhos, dos quais emergiram 19 fêmeas e 16 machos, de cavidades com diâmetros 0,6 0,8 e 1,1 cm. O período de nidificação, dezembro e janeiro, ocorreu na estação mais seca. As abelhas constroem seus ninhos utilizando uma resina vegetal vermelha, levada para o ninho pelas mandíbulas e primeiro par de pernas. Os ninhos são constituídos de uma série linear de células de cria com as paredes construídas com resina, sem adição de outro material. O comprimento médio dos ninhos foi 59,4 mm (n = 10 ninhos). O número médio de células por ninho foi de 6,6 (n = 10). O comprimento das células variou de 6,5 mm a 10,0 mm (n = 10). Os casulos contendo fêmeas foram significativamente maiores em comprimento e diâmetro que os casulos contendo machos. A mortalidade de imaturos por ninho variou de 0 a 100%. Fungos e um microhimenóptero parasita foram responsáveis pela alta taxa de mortalidade. O período de nidificação de A. lunatus foi curto, na estação mais seca do ano. Os imaturos permaneceram em diapausa, no estádio de pré-pupa, durante cerca de 10 meses. Ocorreu uma única geração por ano (espécie univoltina).

IMPACTS OF NEST CONSTRUCTION BY NATIVE PIGS (SUS SCROFA) ON LOWLAND MALAYSIAN RAIN FOREST SAPLINGS

Isolation of remnant forest patches, coupled with anthropogenic changes in the surrounding landscape, often leads to changes in the population density of forest-dwelling mammals. At Pasoh Forest Reserve in Peninsular Malaysia, densities of native wild pigs (Sus scrofa) are 10–100 times greater than historical levels due to the local extinction of feline predators and the presence of abundant food sources in areas adjacent to the forest. Female pigs build reproductive nests out of understory vegetation; at Pasoh these nests are constructed primarily of woody saplings several meters tall that pigs snap or uproot, causing substantial local damage. We documented the prevalence of nest building by pigs at Pasoh within a 25-ha area from 1995 to 1998 and investigated the impacts of this mammalian behavior on the understory plant community. In total, 643 pig nests were enumerated, providing an estimate that 6.0 nests·ha−1·yr−1 were constructed in the survey area. Pigs avoided constructing nests adjacent to trails but otherwise built nests throughout the 25-ha survey area. A single pig nest contained, on average, 267 ± 86 (mean ± 1 sd) woody saplings, of which 45% had been uprooted and 55% had the main stem snapped. The understory area affected by the construction of a single pig nest averaged 244 ± 112 m2, with 53% of all free-standing woody plants ≥70 cm tall and <2.0 cm dbh in this area being uprooted or snapped. As a result of nest building, pigs caused an estimated 29% of the observed tree mortality of saplings 1–2 cm dbh, and 43% of sapling mortality and damage combined. Pigs affected plant families differently, with individuals from the economically and ecologically paramount Dipterocarpaceae being about two times more likely to be used in nest construction than other taxa. Our results indicate that pig nest-building activities are a major source of sapling mortality, and that their effects probably will result in substantial shifts in tree community composition in this forest.

Nest-building behaviour in male rats from three inbred strains: BN/HsdCpb, BDIX/Or1Ico and LEW/Mol

AbstractThree inbred strains of male laboratory rat (BN/HsdCpb, BDIX/Or1Ico and LEW/Mol) were provided with nest boxes and nest materials, and were observed for nest-building activity. After 7 days, each cage and nest box was examined. Each nest was weighed and scored for complexity, and returned to the cage. This was repeated after a further 7 days and the nest removed completely. This routine was repeated three times. All three strains of rat built nests inside the nest box and showed the same stages of construction. There was a significant increase in nest complexity between day 7 and day 14 in the strains BN and BDIX. Furthermore, BDIX rats used significantly more material for the nests, compared with the BN and LEW rats. In a second experiment, using the same rats, nest material was offered in four different ways. LEW rats used nesting material irrespective of where it was placed; BN rats only used straw placed on the top of the cage when no alternative was provided in the cage, and would not use the nest box roof when it was covered with bedding; whereas BDIX rats would only use nest material placed within the cage and would not use straw placed on the cage lid. BN rats also used nest material to cover the entrance to the nest box, a practice not carried out by the other strains. This study demonstrates that these rat strains have retained their natural nest-building behaviour. We suggest that the correct stimuli must be provided in order for this behaviour to be exhibited; in addition, the way in which the nest materials are provided must be in accordance with strain-specific characteristics.

How multidisciplinary is pressure ulcer care?

l like May. Not only does it bring two bank holidays in one month, lambs and frenetic nest-building activity, it also holds endless possibilities: will it snow or rain over that long-awaited bank holiday? Will Arsenal win the FA Cup? What will be the hot topic at the wound societies’ conferences this year?

Crushing of piglets by the mother sow ( Sus scrofa)—purely accidental or a poor mother?

Around 50% of the postnatal death in piglets is caused by crushing or overlying by the domestic sow ( Sus scrofa) when they are kept loose in a farrowing pen. To solve some of these problems, much research attention has been directed towards the farrowing environment. However, previous experiments show that within one farrowing environment there is a large variation in piglet mortality among sows (e.g. [Wechsler, B., Hegglin, D., 1997. Individual differences in the behaviour of sows at the nest-site and the crushing of piglets. Appl. Anim. Behav. Sci. 51, 39–49.]), and recent studies suggest that individual differences in maternal behaviour may explain some of this variation. The aim of the present study was therefore to investigate differences in behavioural characteristics related to maternal abilities between sows that crush several of their piglets and those that do not crush any of their piglets. A sample of 59 healthy, hybrid (Landrace × Yorkshire) sows were video recorded from 2 days before until 4 days after farrowing. From this material, 11 that had not crushed any of their piglets (‘Non-crushers’) within the first 4 days after farrowing and 11 sows that had crushed two or more of their piglets (‘Crushers’) within the same time period, were selected for further behavioural tests and analysis. Sows that did not crush any of their piglets showed a more protective mothering style (i.e. performed more nest building activity, responded sooner on piglet distress calls, initiated nose contacts sooner after presentation of distress calls, nosed more on the piglets during posture change, were more restless when the piglets were taken away) and were socially more flexible (avoided conflicts to a larger extent) in a grouping situation than sows that crushed several piglets. Crushing as a cause of neonatal death in piglets is therefore highly related to mothering style.

Structural and behavioural consequences of double deficiency for creatine kinases BCK and UbCKmit

The cytosolic brain-type creatine kinase (BCK) isoform and the mitochondrial ubiquitous creatine kinase (UbCKmit) isoform are both important for the maintenance and distribution of cellular energy in neurons and astrocytes. Previously, we reported that mice deficient for BCK or UbCKmit each showed a surprisingly mild phenotype, probably due to reciprocal functional compensation by the remaining creatine kinase. This study shows that adult male mice lacking both creatine kinase isoforms (CK--/-- double knockout mice) have a reduced body weight, and demonstrate a severely impaired spatial learning in both a dry and a wet maze, lower nestbuilding activity and diminished acoustic startle reflex responses when compared to age-matched male wildtype mice with the same genetic background. In contrast, their visual and motor functions, exploration behaviour, prepulse inhibition and anxiety-related responses were not changed, suggesting no global deficit in sensorimotor function, hearing or motivation. Morphological analysis of CK--/-- double knockout brains revealed a reduction of ∼7% in wet brain weight and hippocampal size, a ∼15% smaller regio-inferior and relatively larger supra-pyramidal, and intra-infra-pyramidal mossy fiber areas. These results suggest that lack of both brain specific creatine kinase isoforms renders the synaptic circuitry in adult brain less efficient in coping with sensory or cognitive activity related challenges.

Artificially induced group display and nesting behaviour in a reintroduced population of Caribbean Flamingo Phoenicopterus ruber ruber

Summary We used artificial social stimulation (decoys, vocalization playbacks, and artificial nests) to initiate group displays in six (two females, four males) Caribbean Flamingos Phoenicopterus ruber ruber that had not successfully bred since their introduction to Guana Island, British Virgin Islands, in 1992. During a control period prior to the introduction of stimuli, flamingos exhibited no social displays or nest building activities. All flamingos were observed approaching the decoy area as a flock within four hrs of the decoys being introduced, and Head-Flagging displays were exhibited by two birds within the first 24 hrs. In a 12-hr watch conducted two-weeks post decoy introduction, there were significantly more group display behaviours, as well as nest-building, as compared with the control period and immediately after the introduction (3.6% as compared with 0% and 0.35%). Two individuals performed the majority of group displays (although at least one social display posture was observed for each bird) and three birds exhibited nest-building behaviour. Overall, individuals spent most of their time feeding and resting/sleeping (> 95%) during all observation periods. We show for the first time that decoys and vocalization playbacks could have a positive impact on breeding success in the wild by inducing group displays and nesting behaviours in this group of introduced flamingos. We suggest that social attraction techniques may be a useful tool to stimulate breeding in small captive and wild small populations of flamingos.

Factors influencing susceptibility of host nests to brood parasitism

We investigated susceptibility of Song Sparrow (Melospiza melodia) nests to discovery by nest-searching Brown-headed Cowbirds (Molothrus ater) at Delta Marsh, Manitoba. We assessed the importance of nest habitat and microhabitat as well as host activity in influencing the likelihood of parasitism by measuring vegetation and behaviour of hosts at nests that were (1) not parasitized, (2) parasitized once and (3) parasitized more than once, by the same female or by more than one female (i.e. multiple parasitism). None of the variables measured was significantly related to parasitism, but non-significant trends consistent in both years of the study suggested that concealment and host conspicuousness play important roles, but quantifying them is difficult and complex. A significant relationship between nest mass and the probability of parasitism further supports this suggestion, because nest mass should reflect nest-building activity as a whole.

Parental care in the captive mandarin vole, Lasiopodomys mandarinus

Based on the social structure of free-living mandarin voles (Lasiopodomys mandarinus), high paternal investment might be expected for this species. This prediction was tested under laboratory conditions. We observed 10 pairs rearing their first litter. All pairs exhibited permanent nest cohabitation. Females never prevented males from entering the natal nest. Males exhibited all the patterns of direct care of young except nursing: huddling over, brooding with kyphosis, grooming, manipulating, and retrieving young. There were no sex differences in total time spent in the nest or in time spent alone. Females spent more time grooming pups than did males. There was no sex difference in nest-building activity. The frequency of bringing food or nest material into the nest, as well as in digging time, was significantly greater for males than for females. In L. mandarinus the biparental rearing system with a high level of direct paternal care and some division of labour between the parents seems to be associated with the subterranean mode of life. This pattern of parental care can be predicted for other specialized fossorial voles.

Does feed-back from a nest affect periparturient behaviour, heart rate and circulatory cortisol and oxytocin in gilts?

To determine the effects of feed-back from a farrowing nest on periparturient behaviour, heart rate and hormones, 20 gilts housed in Schmid pens were permitted to build a nest of peat, straw and branches. Ten gilts then had their nest removed (NR) 10h after the onset of nest-building and again every 4h until parturition, whereas 10 gilts were given sham removals (C). Based on video recordings, gilt periparturient postures and nest-building behaviour were observed from 7h before until 6h after the birth of the first piglet. Maternal heart rate was measured using a transmitter belt and a watch receiver and the heart rate during the last 7h prepartum analysed. Maternal blood samples were taken via a jugular catheter every 20min over the last 7h prepartum and later analysed for plasma concentrations of cortisol and oxytocin.Treatment did not affect the quantity or timing of nest-building and postural behaviour prior to or during parturition. However, treatment significantly affected changes over time in heart rate and plasma cortisol as parturition approached. Heart rate (P=0.008) and plasma cortisol (P=0.002) increased for NR gilts, but remained constant for C gilts, although nest-building activity decreased during this period in both groups (P=0.006). Plasma oxytocin was unaffected by treatment. The prepartum increases in plasma cortisol and heart rate in NR gilts in the absence of greater activity suggest that nest removal was stressful. The observed treatment effects could have resulted from gilts perceiving environmental novelty following nest disruption, a specific lack of feed-back from the nest or disturbance from nest removal activity per se. The results emphasise the importance of the farrowing environment and the opportunity to construct a nest on sow welfare.

Pituitary-Adrenal Activation in Pre-Parturient Pigs (Sus Scrofa) is Associated with Behavioural Restriction Due to Lack of Space Rather than Nesting Substrate

AbstractPrevious research has shown that pre-parturient primiparous pigs (gilts) housed in behaviourally restrictive farrowing crates without straw redirect their nest-building behaviour to non-manipulable substrates such as the bars of the crate. These gilts also show elevated plasma adrenocorticotropic hormone (ACTH) and Cortisol levels, particularly around the peak of nest-building activity, when compared to gilts in larger pens that have been provided with a manipulable substrate (straw). It remains unclear whether these behavioural and physiological responses to crating result from the lack of a suitable nesting substrate or from the restricted space. This study investigated the effects of space (crate [C] versus pen [P] and straw (straw [S] versus no straw [NS]) using a 2 × 2 factorial design. Thirty-four gilts were implanted with an indwelling jugular catheter at around 12 days before parturition. They were moved to one of the four environments five days before parturition, and blood sampling and recording of behaviour were carried out during the pre-parturient period. Penned gilts (P), irrespective of straw availability, spent more time standing and walking and performed more total substrate-directed behaviour than crated (C) gilts. When straw was not available to penned gilts, a large proportion of their substrate-directed behaviour was redirected to the floor. Space also had an effect on ACTH and Cortisol levels across the entire pre-parturient phase, with C gilts having higher levels than P gilts irrespective of straw availability, but particularly so at the peak of nest-building activity. There was no effect of straw on ACTH or Cortisol levels. Overall, it appears that increased space, perhaps through allowing locomotion, increases substrate-directed behaviour of pre-parturient gilts. When space is available but straw is absent, pre-parturient gilts redirect their nest-building behaviour to the floor. The ability to express substrate-directed behaviour as a result of increased space is reflected in lower levels of indicators of physiological stress.

C-fos mRNA expression associated with PGF 2α-induced nest-building behaviour in female pigs

Domestic pigs, Sus scrofa, build a maternal nest on the day before parturition. A model for nest building has been established in pigs, in which exogenously administered prostaglandin (PG) F 2α may be used to elicit nesting behaviour in cyclic, pseudopregnant and pregnant pigs. The central mechanisms mediating this response are unknown. The present study determined regional brain activity using semi-quantitative analysis of c-fos mRNA, after induction of nest-building behaviour by PGF 2α in Large White pseudopregnant pigs. Oestradiol valerate injections (5 mg/day) were given on days 11–15 of the oestrous cycle to induce pseudopregnancy. The pigs were housed individually in pens (2.8×1.7 m) containing straw. On the test day (day 46 or 47 of pseudopregnancy) animals were injected with 3 ml saline ( n=5) or 15 mg of PGF 2α (Lutalyse, Upjohn; n=6) intramuscularly. Pigs treated with PGF 2α, but not saline, displayed bouts of rooting, pawing and gathering straw, which we interpret as nest building behaviour. The pigs were killed 65 min after treatment, which was 30 min after peak nest building activity, and the brain, uterus and ovaries removed for processing using in situ hybridisation. Saline-treated pigs had elevated levels of c-fos mRNA, compared to background, in the pituitary, corpus luteum and uterus, and a lower, but elevated, level of expression in cerebellum, cortex, hippocampus and olfactory bulb. PGF 2α-treated pigs had significantly higher levels of c-fos mRNA expression than saline-treated pigs in the parvocellular and magnocellular regions of the hypothalamic paraventricular nucleus, the supraoptic nucleus (including the pars dorso-medialis), the neural lobe of the pituitary gland and the cerebellum. PGF 2α-treated pigs also had significantly higher c-fos induction in corpus luteum. These data show that the pattern of c-fos mRNA expression in specific brain areas is different between pigs that show PGF 2α-induced nest building and saline-injected controls.

Nest-building activity and laying date influence female reproductive investment in magpies: an experimental study

Nest size or nest-building activity has recently been hypothesized to be a postmating sexually selected signal in monogamous birds: females may assess a male's parental quality and willingness to invest in reproduction by his participation in nest building. Females may thus adjust their reproductive effort (i.e. clutch size) not only to their own abilities but also to those of their mates. We investigated whether female magpies, Pica pica, use nest-building activity rather than nest size to adjust their reproductive effort during replacement breeding attempts. After we removed their first clutch, high-quality pairs that built a large nest for the first clutch were more capable of building a replacement nest and females adjusted their clutch size in relation to the time it took to build the nest rather than nest size. We also found support for the hypothesized trade-off between clutch size and egg size in magpies. In replacement clutches females decreased clutch size and increased egg volume, thereby probably improving the survival probability of their offspring in less favourable conditions.Copyright 2002 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour

An analysis of travel costs on transport of load and nest building in golden hamster

We investigated the effects of travel costs on transporting nest material and nest-building activity in golden hamsters. Nest-deprived animals were submitted to run alleys 30, 90 and 180 cm long to access a source containing paper strips as nest material (Experiment 1) or were submitted to the same travel costs in 24-h experimental sessions (Experiment 2). We noted that increased travel costs were related to a decreased number of trips to the source, larger amounts (cm 2) of nest material transported per trip (although total loads also decreased in longer alleys), longer intervals between trips, and increased time spent at the source and in nest building activity. Foraging efficiency (i.e. size of load divided by the time spent at the source) decreased as a function of travel costs, and animals transported their loads in two fundamental ways: in 30-cm alleys, they simply used their mouth to pull the paper strips, but in 90- or 180-cm alleys they transported the loads in their cheek pouches. The animals were faster when returning to the home-cage and their running speed (cm/s) increased as a function of the length of the alley, showing that animals are under different environmental pressures when searching for resources and subsequently running back with the load to the nest. Both male and female subjects were sensitive to travel costs, but males engaged in nest building activity more promptly and exhibited higher mean performances in most measures. We conclude that nest material is a good reinforcer, and our major results are in accordance with the predictions of microeconomic and optimal foraging theories.

Facultative and obligate slave making in Formica ants.

Here we show for the first time that the presumed facultative slave-making ant Formica subintegra does not activate outside its nest until July and August, when it raids slaves. A comparative behavioral study of seasonal and daily activities, retrieval of prey, and nest maintenance of F. subintegra, the obligate slavemaker Polyergus breviceps, and the facultative Formica subnuda, shows that the behavioral repertory of F. subintegra closely resembles that of P. breviceps and clearly differs from the repertory of F. subnuda. Unlike P. breviceps, F. subintegra has retained some nest-building activity which, owing to lack of competence, does not contribute to nest maintenance. We suggested earlier that F. subintegra is probably an obligate slavemaker, because it always has in its colonies a large proportion of slaves of the total workforce, whereas F. subnuda fares well even without slaves. This, coupled with no foraging in early summer and a raiding period later on, strongly suggests that F. subintegra is an obligate slave-making ant.