Pilfering ravens, Corvus corax, adjust their behaviour to social context and identity of competitors

Like other corvids, food-storing ravens protect their caches from being pilfered by conspecifics by means of aggression and by re-caching. In the wild and in captivity, potential pilferers rarely approach caches until the storers have left the cache vicinity. When storers are experimentally prevented from leaving, pilferers first search at places other than the cache sites. These behaviours raise the possibility that ravens are capable of withholding intentions and providing false information to avoid provoking the storers' aggression for cache protection. Alternatively, birds may refrain from pilfering to avoid conflicts with dominants. Here we examined whether ravens adjust their pilfer tactics according to social context and type of competitors. We allowed birds that had witnessed a conspecific making caches to pilfer those caches either in private, together with the storer, or together with a conspecific bystander that had not created the caches (non-storer) but had seen them being made. Compared to in-private trials, ravens delayed approaching the caches only in the presence of storers. Furthermore, they quickly engaged in searching away from the caches when together with dominant storers but directly approached the caches when together with dominant non-storers. These findings demonstrate that ravens selectively alter their pilfer behaviour with those individuals that are likely to defend the caches (storers) and support the interpretation that they are deceptively manipulating the others' behaviour.This contribution is part of the special issue “Animal Logics” (Watanabe and Huber 2006).     

Leaving patches: effects of economy, deprivation, and session duration

Three pigeons pecked keys for food reinforcers in a laboratory analogue of foraging in patches. Half the patches contained food (were prey patches). In prey patches, pecks to one key occasionally produced a reinforcer, followed by a fixed travel time and then the start of a new patch. Pecks to another key were exit responses, and immediately produced travel time and then a new patch. Travel time was varied from 0.25 to 16 s at each of three session durations: 1, 4, and 23.5 hr. This part of the experiment arranged a closed economy, in that the only source of food was reinforcers obtained in prey patches. In another part, food deprivation was manipulated by varying postsession feeding so as to maintain the subjects' body weights at percentages ranging from 85% to 95% of their ad lib weights, in 1-hr sessions with a travel time of 12 s. This was an open economy. Patch residence time, defined as the time between the start of a patch and an exit response, increased with increasing travel time, and consistently exceeded times predicted by an optimal foraging model, supporting previously published results. However, residence times also increased with increasing session duration and, in longer sessions, consistently exceeded previously reported residence times in comparable open-economy conditions. Residence times were not systematically affected by deprivation levels. In sum, the results show that the long residence times obtained in long closed-economy sessions should probably be attributed to session duration rather than to economy or deprivation. This conclusion is hard to reconcile with previous interpretations of longer-than-optimal residence times but is consistent with, in economic terms, a predicted shift in consumption towards a preferred commodity when income is increased.     

Political Power and Race Relations in South Africa: African Attitudes Before and After the Transition

When an oppressed majority finally gains political power, what happens to its attitudes to its erstwhile oppressor, and to its perceptions and feelings about its socioeconomic disadvantages that were established during its oppression? Longitudinal data from pre- and post-transition surveys of black South African college and high school students indicate marked reductions in perceptions of and outrage about intergroup socioeconomic inequity and deprivation relative to English-speaking and Afrikaans-speaking whites, but no change in attitudes toward these groups or toward whites in general. The findings are discussed in terms of contemporary theory and research on justice, intergroup relations, and group conflict. Some tentative implications for the prospects for a democratic political culture in South Africa are noted.     

Infant food refusal and parental social support

The purpose of this study was to examine the relations between various aspects of social support and maternal and infant outcome variables in a group of families having infants showing food refusal compared to a control group. In the case of early food refusal, the results indicated that access to emotional support and satisfaction with support were related to maternal psychosomatic health. The relationships were interpreted as showing that social support has moderating effects on negative outcomes of food refusal.     

Response deprivation, reinforcement, and economics

Reinforcement of an instrumental response results not from a special kind of response consequence known as a reinforcer, but from a special kind of schedule known as a response-deprivation schedule. Under the requirements of a response-deprivation schedule, the baseline rate of the instrumental response permits less than the baseline rate of the contingent response. Because reinforcement occurs only if the schedule deprives the organism of the contingent response, reinforcement cannot result from any intrinsic property of the contingent response or any property relative to the instrumental response. Two typical effects of response-deprivation schedules—facilitation of the instrumental response and suppression of the contingent response—are discussed in terms of economic concepts and models of instrumental performance. It is suggested that response deprivation makes the contingent response function as an economic good, the instrumental response as currency.     

ESTABLISHING OPERATIONS AND REINFORCEMENT EFFECTS

Positive reinforcement procedures have had a major impact on educational programs for the developmentally disabled; nevertheless, variation in reinforcer effectiveness both within and across individuals is a common phenomenon. This study examined one class of variables—establishing operations—that might influence the effectiveness of reinforcers. Five developmentally disabled adult males participated. Responding on one of two motor tasks—switch closure or block placement—was assessed during baseline, satiation, and deprivation conditions with respect to three classes of consequences: small food items, music, and social praise. Deprivation and satiation conditions were constructed so as not to alter significantly the normal course of events in a subject's day. For example, food deprivation entailed scheduling sessions just prior to a subject's regular lunch, and social deprivation involved limiting a subject's access to social interaction for 15 minutes, during which time the subject had access to an assortment of other activities. Results showed that each stimulus class functioned as reinforcement with different degrees of effectiveness during satiation versus deprivation conditions. These results are discussed in light of previous research on enhancement of reinforcer efficacy as well as the assessment and identification of functional reinforcers, and implications are presented for future research and client habilitation.     

Effects of search cost on foraging and feeding: a three-component chain analysis

An experiment determined whether pigeons minimize number of key pecks per food delivery and maintain their baseline intake of food while key pecking on a three-component chain schedule. Pigeons at either 80% or 100% body weight obtained all their food during baseline and contingency sessions. During baseline sessions, pecks on the left and center keys had no consequences; each peck on the right key activated the feeder. During contingency sessions, pigeons key pecked on a three-component chain schedule simulating components of a foraging chain. In the search component either 3, 9 or 15 key pecks (varied parametrically across blocks of sessions) on the left key produced a stimulus on the middle key, indicating an encounter with either the low-cost prey (3 key pecks) or an equally probable high-cost prey (21 key pecks). In the procurement component the pigeon pecked either: (a) the left key once, thus returning to the search component, or (b) the middle key either 3 or 21 times, which activated the right response key. In the handling component one peck on the right key operated the feeder. The pigeons always procured the low-cost prey and minimized the number of key pecks per hopper by procuring the high-cost prey when the search-cost ratio was high (15 key pecks) but not when it was low (3 key pecks). All pigeons maintained their baselines of eating during contingency sessions by key pecking more frequently and eating more efficiently. The 80% body-weight birds produced higher overall rates of key pecking and eating. These results have implications for ecological theories of optimal foraging and for psychological theories of learned performance.     

睡眠剥夺与购物后悔：来自大规模个体层面数据的证据

睡眠剥夺正在成为人们面临的一种普遍问题,但是已有研究很少将睡眠剥夺与消费者行为联系起来。本文采用真实购物情境下的大规模消费者个体层面数据(N=1625472),通过建立计量经济学模型来研究睡眠剥夺与购物后悔的关系。结果表明,睡眠剥夺显著地增加了消费者的购物后悔倾向,具体在行为上表现为增加了商品的退货概率和加快了商品的退货速度。此外,商品的价格正向调节了睡眠剥夺对购物后悔的影响,而促销优惠金额的比例则负向调节了睡眠剥夺对购物后悔的影响。     

Effects of foster care intervention and caregiving quality on the bidirectional development of executive functions and social skills following institutional rearing

Institutional rearing negatively impacts the development of children's social skills and executive functions (EF). However, little is known about whether childhood social skills mediate the effects of the foster care intervention (FCG) and foster caregiving quality following early institutional rearing on EF and social skills in adolescence. We examined (a) whether children's social skills at 8 years mediate the impact of the FCG on the development of EF at ages 12 and 16 years, and (b) whether social skills and EF at ages 8 and 12 mediate the relation between caregiving quality in foster care at 42 months and subsequent social skills and EF at age 16. Participants included abandoned children from Romanian institutions, who were randomly assigned to a FCG (n = 68) or care as usual (n = 68), and a never-institutionalized group (n = 135). At ages 8, 12, and 16, social skills were assessed via caregiver and teacher reports and EF were assessed via the Cambridge Neuropsychological Test Automated Battery. Caregiving quality of foster caregivers was observed at 42 months. FCG predicted better social skills at 8 years, which in turn predicted better EF in adolescence. Higher caregiver quality in foster care at 42 months predicted better social skills at 8 and 12 years, and better EF at 12 years, which in turn predicted 16-year EF and social skills. These findings suggest that interventions targeting caregiving quality within foster care home environments may have long-lasting positive effects on children's social skills and EF.