There is limited research into mesolimbic function specific to birds and, specifically, how neurobiological reward mechanisms affect learning in domestic laying hens (Gallus gallus domesticus). A more thorough understanding of these mechanisms has implications for the improvement of welfare. Reward is proposed to involve two separate processes of 'wanting' regulated by dopamine and 'liking' regulated by opioids. This study examined the effect the opioid antagonist, nalmefene, on learning in domesticated hens.

Eighteen Isa Brown hens were randomly assigned into either a saline or nalmefene treatment group. Hens in the saline group (N = 9) received 0.9 % saline (0.5 mL/kg pectoral muscle injection). Hens in the nalmefene treatment group (N = 9) were administered an opioid antagonist (0.4 mg/kg nalmefene in 0.9 % saline pectoral muscle injection) to disrupt the reward pathway. Prior to administration of treatments, hens were habituated to the training table, cup and trainer. Training occurred over three consecutive days on a series of three tasks using operant conditioning. Hens were dosed with either saline or nalmefene thirty minutes prior training. Hens were trained for one five minute session each day. Learning tasks included (1) pecking a target, (2) colour stimulus discrimination, and (3) pecking a target on cue presentation. All tasks were trained by the same trainer who was blind to treatment, using clicker training to shape responses. By the final day of training (Day 3), more saline hens had completed Task 1 and Task 2 than hens that received nalmefene (P < 0.0001). No hens in the nalmefene treatment group completed any training task. This study demonstrates that hens treated with an opioid antagonist failed to learn any tasks during operant training sessions, using a food reinforcer, over three days. We show that hens did not learn when the ability to experience reward is blocked, providing evidence that performing operant tasks is rewarding to hens.

The Noisy Miner (Manorina melanocephala) is a cooperative honeyeater living in social groups throughout south-east Australia that displays high levels of interspecific aggression and reduces avifaunal biodiversity in areas it occupies. Human-induced habitat changes have also potentially increased the availability of high-quality habitat and food resources available for Noisy Miners, which may in turn affect activity budgets and the duration or intensity of aggression displayed by Miners towards other species. To quantify the impact of differences in the potential availability of anthropogenic food resources on Noisy Miner aggression levels, we presented taxidermy models from three different categories of bird species (food competitors, non-food competitors and potential predators) and quantified observed aggression in three separate habitats: natural areas with very limited additional anthropogenic food resources, gardens that provided supplementary resources such as nectar-rich ornamental plants, and cafes that provided access to human food items. As predicted, Noisy Miners exhibited agonistic behaviours for a significantly longer period in the habitats with anthropogenic food resources, namely gardens and cafes in comparison to natural areas. The type of model presented also impacted Miner response, with: (1) greater numbers of Miners mobbing predator rather than competitor models, (2) Miners mobbing predator models for longer periods than competitors, and (3) a greater probability of Miners physically contacting competitor models. These findings demonstrate that additional resources have the ability to impact time budgets of species and, for hyperaggressive birds such as Noisy Miners, can impact biodiversity in more nuanced ways than previously quantified.