Alimentary Canal: Anatomy, Prehension, Deglutition, Feeding, Drinking, Passage of Ingesta, and Motility

Hacking techniques improve health and nutritional status of nestling White-tailed Eagles

Birds of prey frequently feature in reintroductions and the hacking technique is typically used. Hacking involves removing large nestlings from donor populations, transferring them to captivity, feeding them ad libitum. Potentially, via the hacking method, the stress of captivity and disruption of parental feeding may be detrimental. Alternatively, the provision of ad libitum food may be advantageous. Although hacking has underpinned reintroduction project successes there has been no research on how the method may affect the health and nutritional status of translocated birds during captivity. We compared blood chemistry data from 55 young White-tailed Eagles, translocated from Norway as part of the species' reintroduction to Scotland, from sampling soon after arriving in captivity and again (≈42 days later) before their release. Numerous significant differences between the first and second samples were found, but no significant interactions showed that the sexes responded similarly to captivity. According to hematological and biochemical metrics, individuals showed several changes during captivity, including in red blood cell parameters, plasma proteins, and white cellular parameters related to the immune system, that indicated improved health status. Captivity with ad libitum food was associated with decreased urea and uric acid values: high values can indicate nutritional stress. Urea values became more normally distributed before release, indicating that ad libitum food had reduced nutritional differences between early nestlings in the season and later ones. Despite plentiful food, both sexes lost body mass before release, suggesting an inherent physiological mechanism to improve flight performance in fledglings. We conclude that hacking improved the health and nutritional status of released eagles which is likely to enable birds to cope with greater costs of exploratory behavior which they may require in reintroduction projects. In this context, we note the absence of survival differences between hacked and wild raptors in previous research.

A method of achieving physiological plasma levels of melatonin in the chicken by oral administration

In avian species it has been difficult to elucidate the precise role of melatonin in the control of reproductive cycles. We have investigated ways of administering melatonin to immature chickens and laying hens to achieve physiological levels and patterns in blood simulating either short or long photoperiods. Melatonin was administered orally using different doses and various ways of applying melatonin to the feed. For subcutaneous injections, melatonin was suspended in propylene glycol or grape seed oil. Melatonin always appeared in the first blood samples taken within an hour of administration. When melatonin was absorbed into feed pellets or whole wheat, a high initial plasma concentration was reached, followed by a rapid decrease over the ensuing 2-3 hr, but was still detectable as long as 24 hr after administration. For example, doses of 300 microg/kg produced 15 nM, which is more than ten times higher than the nocturnal peak concentration. When melatonin was absorbed into cracked wheat grains that were subsequently washed with ethanol, the initial transitory peak was eliminated, levels in plasma were sustained for at least 12 hr in the normal nocturnal range (750 pM), and no melatonin (< 60 pM) was present 18 hr later. When injected (2 microg/bird), concentrations peaked (610 pM) within 30 min and decreased rapidly over the next 2-3 hr. It was concluded that melatonin-treated, ethanol-rinsed cracked wheat grains can be used to experimentally mimic long-night plasma melatonin patterns. Injections may be useful for mimicking the melatonin patterns of very short nights in chickens experiencing constant light.