Does Functional Lateralization in Birds Have any Implications for Their Welfare?

Abstract

We know a good deal about brain lateralization in birds and a good deal about animal welfare, but relatively little about whether there is a noteworthy relationship between avian welfare and brain lateralization. In birds, the left hemisphere is specialised to categorise stimuli and to discriminate preferred categories from distracting stimuli (e.g., food from an array of inedible objects), whereas the right hemisphere responds to small differences between stimuli, controls social behaviour, detects predators and controls attack, fear and escape responses. In this paper, we concentrate on visual lateralization and the effect of light exposure of the avian embryo on the development of lateralization, and we consider its role in the welfare of birds after hatching. Findings suggest that light-exposure during incubation has a general positive effect on post-hatching behaviour, likely because it facilitates control of behaviour by the left hemisphere, which can suppress fear and other distress behaviour controlled by the right hemisphere. In this context, particular attention needs to be paid to the influence of corticosterone, a stress hormone, on lateralization. Welfare of animals in captivity, as is well known, has two cornerstones: enrichment and reduction of stress. What is less well-known is the link between the influence of experience on brain lateralization and its consequent positive or negative outcomes on behaviour. We conclude that the welfare of birds may be diminished by failure to expose the developing embryos to light but we also recognise that more research on the association between lateralization and welfare is needed.

Relationships Between Rearing Enrichments, Range Use, and an Environmental Stressor for Free-Range Laying Hen Welfare

“…Further studies could also measure the rate of adaptation following the removal of an imposed stressor, which was not assessed in this study, including measuring the use of the available range area rather than just time and visits outside. It is possible that the structural enrichments during rearing resulted in neurological changes such as greater hemispheric flexibility that improved adaptive responses to their environments (43). Previous comparisons between cage-reared and aviary-reared hens showed functional lateralization in the hippocampus and caudolateral nidopallium but no differences between the rearing treatments, although all birds were in similar environments for the first 4 weeks of rearing (44).…”

“…The welfare scoring data including the live weight, number of comb wounds, beak score, keel score, plumage score (total), and toenail length at different age points (25,33,43,56,64 weeks) throughout the laying cycle for individual hens from different rearing treatments were compiled (n = 6,876 data points/welfare parameter except for the beak score data which had n = 5,492 data points as beaks were not scored at the 25 week assessment date). The number of comb wounds and plumage score data were square-root-transformed, and the toenail length data were log 10 -transformed.…”

“…The mean ± SEM of the number of comb wounds in hens from different rearing treatments (control, novelty, structural) at different age points(25,33,43, 56, 64 weeks) in their laying cycle. The rearing treatments and age of hen interacted significantly (P < 0.0001).…”

Rearing Enrichments Affected Ranging Behavior in Free-Range Laying Hens

“…A lateralized brain will improve the ability to respond to concurrent stimuli (e.g., searching for food while under threat from a predator) (36) and likely has implications for animal welfare such as the display of a negative bias or an elevated response to stressful situations (37,38). The left hemisphere controls established behavioral patterns compared with the right hemisphere that attends to unexpected stimuli; an overview of the hemispheric specializations is provided in Rogers (36) and Rogers and Kaplan (38).…”

“…A lateralized brain will improve the ability to respond to concurrent stimuli (e.g., searching for food while under threat from a predator) ( 36 ) and likely has implications for animal welfare such as the display of a negative bias or an elevated response to stressful situations ( 37 , 38 ). The left hemisphere controls established behavioral patterns compared with the right hemisphere that attends to unexpected stimuli; an overview of the hemispheric specializations is provided in Rogers ( 36 ) and Rogers and Kaplan ( 38 ). The different types of enrichments provided may have either improved the degree of hemispheric flexibility and how the hens react to stimuli and their surrounding environment ( 38 ), or increased the dominance of a specific hemisphere thus altering the main hemisphere attending to the environment.…”