Corvid Re-Caching without ‘Theory of Mind’: A Model

Scrub jays are thought to use many tactics to protect their caches. For instance, they predominantly bury food far away from conspecifics, and if they must cache while being watched, they often re-cache their worms later, once they are in private. Two explanations have been offered for such observations, and they are intensely debated. First, the birds may reason about their competitors' mental states, with a ‘theory of mind’; alternatively, they may apply behavioral rules learned in daily life. Although this second hypothesis is cognitively simpler, it does seem to require a different, ad-hoc behavioral rule for every caching and re-caching pattern exhibited by the birds. Our new theory avoids this drawback by explaining a large variety of patterns as side-effects of stress and the resulting memory errors. Inspired by experimental data, we assume that re-caching is not motivated by a deliberate effort to safeguard specific caches from theft, but by a general desire to cache more. This desire is brought on by stress, which is determined by the presence and dominance of onlookers, and by unsuccessful recovery attempts. We study this theory in two experiments similar to those done with real birds with a kind of ‘virtual bird’, whose behavior depends on a set of basic assumptions about corvid cognition, and a well-established model of human memory. Our results show that the ‘virtual bird’ acts as the real birds did; its re-caching reflects whether it has been watched, how dominant its onlooker was, and how close to that onlooker it has cached. This happens even though it cannot attribute mental states, and it has only a single behavioral rule assumed to be previously learned. Thus, our simulations indicate that corvid re-caching can be explained without sophisticated social cognition. Given our specific predictions, our theory can easily be tested empirically

Exploring knowledge, perception of risk and biosecurity practices among researchers in the UK: a quantitative survey

Accidental introduction and/or spread of Invasive Non-Native Species (INNS) can result from a range of activities including agriculture, transport, trade and recreation. Researchers represent an important group of stakeholders who undertake activities in the field that could potentially facilitate the spread of INNS. Biosecurity is key to preventing the introduction and spread of INNS. Risk perceptions are a fundamental component in determining behaviour, so understanding how researchers perceive the risks associated with their activities can help us understand some of the drivers of biosecurity behaviour in the field. The aim of this study was to investigate researchers’ perceptions of risk in relation to their field activities and whether risk perceptions influenced behaviour. We gathered quantitative data on perceptions of risk and biosecurity practices using an online questionnaire. Only 35% of all respondents considered their field activities to pose some risk in terms of spreading INNS. Higher risk perception was found in those who undertook high risk activities or where INNS were known/expected to be present. However, whilst respondents with experience of INNS were more likely to report consciously employing biosecurity in the field, this did not translate into better actual biosecurity practices. Awareness of biosecurity campaigns did in fact increase perception of risk, perceived and actual biosecurity behaviour. However, there remains a disconnect between reported and actual biosecurity practices, including a lack of understanding about what constitutes good biosecurity practice. These findings should be used to improve targeted awareness raising campaigns and help create directed training on biosecurity practices

Epidemiology of AIDS dementia complex in Europe.

The aim of the study was to describe the epidemiology of AIDS dementia complex (ADC) in Europe and to assess the possible role of zidovudine therapy in preventing or delaying its occurrence. We used an inception cohort, with data collected retrospectively from patients' clinical records from 52 clinical centers in 17 countries across Europe. The subjects were 6,548 adult people with AIDS consecutively diagnosed from 1979 to 1989. The main outcome measures were codiagnosis of ADC at the time of AIDS diagnosis and ADC-free time after AIDS diagnosis. ADC was reported in 295 patients (4.5%) at the time of AIDS diagnosis and during follow-up in a further 402 of the 5,160 patients (7.8%) who were diagnosed with AIDS based on diseases other than ADC. Whether at the time of AIDS diagnosis or later, the occurrence of ADC was significantly associated with age, transmission category, and CD4+ cell counts. The risk was greater in older patients (14 and 19% greater, at AIDS diagnosis and after, respectively, for a 5-year difference in age), in i.v. drug users than in homosexual and bisexual men (89 and 60% greater, at AIDS diagnosis and after, respectively), and for people with lower CD4+ cell counts (14 and 30% greater for a reduction of 1 on the natural log scale). Risk was almost double for women than for men. A significant reduction, of ~40%, was found in the risk of developing ADC after AIDS diagnosis for patients receiving zidovudine therapy, but this effect was present only during the first 18 months of treatment, irrespective of whether treatment began before or after AIDS diagnosis. In conclusion, an increase in the risk of developing ADC either at the time of AIDS diagnosis or thereafter is associated with increasing age, i.v. drug use, and decreased CD4+ cell count. Women tend to have a higher risk of ADC at the time of AIDS diagnosis. Zidovudine therapy appears to have a definite, but time-limited, effect of protecting patients against ADC development after AIDS diagnosis