Although it is known that many birds possess ultraviolet (UV)-sensitive vision, most commercially housed poultry species, as well as species held in zoos, laboratories, or bred for show, are maintained under lighting that is deficient in UV wavelengths compared with normal daylight. UV-sensitive vision has been shown to be important in both foraging and mate-choice decisions. UV-poor conditions, in which information in this waveband is eliminated, could, therefore, present an important welfare issue. Eight European starlings were given a series of preference tests (eight hours per trial, for six days), in which they could choose to feed in one of four channels. Four experimental trials were carried out, during which the channels were covered in either UV-transmitting (UV+) or UV-blocking (UV-) filters, to determine whether birds had an initial preference for feeding in UV-rich environments and whether there was any change in their preference over time. There was an initial preference for the UV+ environment, but this preference declined very rapidly with familiarity, and was absent by the final trial. These results imply that starlings can rapidly adjust their feeding behaviour if faced with unfamiliar light environments and that any initial behavioural changes attributable to UV-deficient environments may be short-lived. However, further work is necessary to establish whether these adjustments occur across a range of species and contexts before any welfare concerns can be ruled out.

There is considerable interest in the role that ultraviolet (UV) cues play in the foraging and mate choice decisions of birds. However, with the exception of the zebra finch, Taeniopygia guttata, it is not yet clear whether ultraviolet preferences are context specific, or whether birds show a general preference for full-avian-spectrum environments (320–700nm) irrespective of the activity in which they are engaged. We investigated whether European starlings, Sturnus vulgaris, and blue tits, Parus caeruleus, show general (nonresource based) or context-specific preferences for full-spectrum environments. We found that neither species showed a general preference for UV-present (UV+) over UV-deficient (UV−) environments, when those environments contained no resources (experiment 1). Furthermore, neither species showed a UV+ preference when cages contained food, water and perches (starlings; experiment 2) or food, perches and heterospecifics (blue tits; Hunt et al. 1999. Animal Behaviour, 58, 809–815). However, both species did show highly significant preferences for UV+ conditions when viewing potential mates. Such experiments are necessary before one can conclude that particular wavebands have specific relevance to mate choice. In fact, our results suggest that the importance of particular wavelength compositions do indeed vary with behavioural context.

As ultraviolet wavelengths are used in normal avian colour perception, the maintenance of captive birds under artificial lighting (which is normally UV‐deficient) may have welfare implications. European starling Sturnus vulgaris juveniles kept in UV‐deficient light environments had significantly higher basal plasma corticosterone concentrations than those kept under full spectrum lighting, in the second of two experimental blocks. UV‐deficient conditions also led to significant changes in behaviour indicative of escape (less perching and more hanging on the cage and pecking at it). However, the birds from the first block, where the interval between transfer to the experimental set‐up from the wild was short (2 days), showed significantly higher basal and maximum plasma corticosterone concentrations than those in the second block and no additional effect of light environment on either corticosterone or behaviour. We hypothesise that this difference between blocks was due to the overriding initial stress of being in captivity swamping any treatment effects. Capture stress had declined in the second set of birds, which entered the experiment after 7–14 days in captivity. Stress effects of UV‐deficient lighting appear small relative to the overall impact of captivity, but may nevertheless become apparent after the initial effects of capture subside.

It is increasingly clear that ultraviolet (UV) wavelengths are a component of normal avian colour perception and influence their behaviour. As artificial lighting is designed to human specifications, and so is usually deficient in UV light, there may be welfare implications for captive birds, with both context-dependent and chronic long-term effects in its absence. Domestic chicks, Gallus gallus domesticus, kept under UV-deficient environments had significantly higher basal plasma corticosterone concentrations and tended to explore less, although not significantly so, suggestive of suboptimal conditions. Chicks under full spectrum lighting had a significantly higher rate of corticosterone rise in response to capture and handling stress than chicks reared without UV, largely because a similar maximum level was reached from lower initial concentrations. These treatment differences in hormonal stress response tended to diminish with age and/or familiarity with humans, in both groups of birds.

Recent research has highlighted the extent to which birds utilise ultraviolet vision in mate choice and foraging. However, neither the importance of the ultraviolet compared with other regions of the visual spectrum nor the use of wavelength cues in other visual tasks have been explored. We assessed the individual choices of zebra finches (Taeniopygia guttata) for different-coloured seeds (red and white millet) under lighting conditions in which filters selectively removed blocks of the avian-visible spectrum corresponding to the spectral sensitivity of the four retinal cone types that subserve colour vision in this species. The effects corresponded to those predicted from the calculated distances between seed types, and between each seed type and the background, in a simple model of tetrachromatic colour space. As predicted for this foraging task, the removal of long-wavelength information had a greater influence than the removal of shorter wavelengths, including ultraviolet wavelengths. These results have important implications for predator-prey interactions and suggest that future studies of natural foraging should consider variations in the light environment.

Recent reviews have highlighted the differences between human and avian vision with regard to temporal resolution and the potential problems it may cause for avian welfare and video playback experiments. Birds tend to have much higher critical fusion frequencies than do humans (>100 Hz vs 50-60 Hz in humans), which means that they perceive light as flickering up to and over 100 Hz. This is higher than most television monitors (which have refresh rates of 50 or 60 Hz) and normal fluorescent lighting (100 or 120 Hz), and because humans find flickering light aversive, it has been suggested that birds will as well. If this were the case, then there would be welfare implications of maintaining them under such lighting and also a potential effect on their behavioral responses in video playback experiments. However, there is some behavioral evidence that indicates that birds do not appear to find flicker aversive and may even prefer flickering lighting. The authors aimed to determine whether a passerine, the European starling, found flicker aversive by measuring the corticosterone stress response in birds maintained under high- or low-frequency fluorescent lighting (35-40 kHz vs 100 Hz) for 1 or 24 h. The results suggest that low-frequency lighting is potentially more stressful because, where differences exist, birds in the low-frequency treatment always showed higher basal corticosterone. However, the evidence is not consistent because in half of the blocks, there were no significant treatment effects and, where there were, the time course of the effects was variable.

Feeding and fat storage entail both costs and benefits. Benefits include minimizing the risk of starvation; costs include mass-dependent costs of locomotion and predation risk. An understanding of these costs and benefits is relevant not only to explanations of foraging patterns and fat storage, but to hoarding decisions, migration strategies, and population dynamics. Despite predictions from theoretical models, empirical tests of the assumptions and predictions of models have been tested only recently. However, published experiments on the effects of unpredictability have often confounded manipulations of mean, variability, and predictability of the food supply, all of which are predicted to affect foraging intensity and fat storage. In experiments on European starlings, Sturnus vulgaris, we manipulated the predictability of the food supply while holding the mean and average variability constant. We did this in conjunction with manipulation of overnight energy expenditure via simulated nocturnal wind exposure. Both greater unpredictability of food availability and higher overnight energy expenditure increased daily mass gain and dusk (lean and fat) mass, but in a purely additive fashion. Dawn mass only changed in response to predictability, not overnight energy expenditure. By introducing a probe day, with identical feeding experience for all treatments, we ascertained that the response to predictability was based on experience integrated over more than a single day.