Tamás, A. & Péczely, P. 1998. Seasonality of sexual steroid plasma levels in Ring-necked Pheasants Phasianus colchicus. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 229.

Captive male Ring-necked Pheasants were studied in an outdoor environment. After an adaptation period, the plasma levels of testosterone (T), 17-B-oestradiol (E2) and progesterone (P4) were determined by RIA. The annual change of the face-lobe, the moulting pattern and the main elements of behaviour were studied. T levels slightly increased in November in relation to the increased aggressivity and with the growing of the face-lobe in autumn. In March, a second increase occurs related to the further development of the face-lobe. In wild birds in this period, territorial and display behaviour develops. The highest T levels occur in April to May, which is the peak of copulation activity in wild pheasants. High E2 levels develop in the middle of June, when the T levels decrease drastically. The strong increase of E2/T ratio determines the beginning of photorefractoriness. A smaller increase of E2 levels develops in November, together with the increase of T and P4 levels. Slight increases in P4 levels in July are related to the postnuptial moulting. Significantly elevated T levels occur in November during the prenuptial moulting and in March in the period of maximal growth of face lobe and maximal length of the "ear-feathers".

Key words: Ring-necked Pheasant, testosterone, 17-B-oestradiol, progesterone, seasonality, photorefractoriness

Hatch, K.A., Pinshow, B., & Porter, W.P. 1998. The use of stable isotopes in assessing substrate metabolism of flying birds. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 229.

It was thought that birds flying long distances catabolised protein only as a last resort after glycogen and lipids were depleted. However, it is increasingly apparent that protein catabolism occurs continuously during long-distance flight and may be an important energy source in some species. We measured ¹³C/¹²C in breath CO₂ to determine the relative contribution of carbohydrates, lipids and proteins to flight metabolism. Endogenous body proteins are enriched in ¹³C relative to a birds diet, while lipids are depleted in ¹³C relative to the diet; carbohydrates have the same value as the diet. Consequently breath CO₂ reflects the metabolic substrate at sampling time. In trained tippler pigeons, we found that: (1) fasting birds used less protein and more lipid to fuel flight than fed birds, (2) fed birds switched from food substrates to endogenous lipids to fuel flight, and (3) longer term fasting induced increased protein catabolism to fuel flight. Once validated for other avian species, in addition to pigeons, this technique will provide a non-lethal, non-invasive method to determine metabolic substrate use in freshly captured migrating birds in the field.

Key words: long-distance flight, protein catabolism, flight metabolism

Van't Hof T.J. & Gwinner, E. 1998. Circadian variation in Zebra Finch Taeniopygia guttata gastrointestinal tract melatonin. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 230.

Recent studies indicate that food can act as a Zeitgeber influencing rhythms in locomotion and activity. In addition, there appears to be a direct relationship between food availability and its strength as a Zeitgeber. It is unclear how the effects of food are mediated. However, when melatonin is administered via drinking water in pinealectomised birds it can also synchronise activity. Therefore, melatonin, if produced in the guts of birds, could regulate activity in the gut as well as influence other parts of the circadian system. Consequently, we examined the levels of melatonin at midday and midnight in ten anatomical sections of the gastrointestinal tract as well as the pineal, eyes and plasma of adult Zebra Finches. Melatonin content was measured by radioimmunoassay after homogenisation and extraction. In the pineal and plasma melatonin levels increased significantly at night. In virtually every gut tissue examined melatonin levels also increased significantly at night. These results suggest that if melatonin is synthesised by gastrointestinal cells in the gut in response to the presence or absence of food in the gut, melatonin could act either directly or indirectly to co-ordinate a suite of activities to prepare the bird for the uptake or loss of food.

Key words: food uptake, gut, Zeitgeber, plasma, pineal

Ménard, J.-J., Fayolle, C., Mioskowski, E., Groscolas, R. & Robin, J.-P. 1998. Metabolic and hormonal response to stress in King Penguin Aptenodytes patagonicus. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 230 - 231.

This study aimed at characterising the response to stress in penguins and at determining how this response is affected by their behaviour and metabolic status. The changes in plasma levels of metabolites and corticosterone were determined in naturally fasting King Penguins during immobilisation stress of various durations (10 to 90 min). In alert birds at the onset of fasting, capture and immobilisation induced a 25 fold rise in the plasma corticosterone, beginning at 5 min. Plasma lactate sharply increased by 10 fold, peaking at 5 min. Plasma NEFA and beta-hydroxybutyrate decreased by 40% within 5 to 10 min and thereafter increased until reaching initial (beta-hydroxybutyrate) or 3-fold higher (NEFA) levels. Plasma glucose rose progressively, by up to 40%. The arousal stage at capture affected the response to stress, the changes in plasma lactate and NEFA being delayed in asleep compared to alert birds. Overall, the response to stress was also affected by the metabolic state: Throughout prolonged fasting, it was maintained as long as birds relied primarily on lipids as an energy source, but was reduced when lipids began to be exhausted. In conclusion, the response to stress in this wild bird is highly variable, depending on the behavioural and metabolic status.

Key words: corticosterone, plasma metabolites, arousal stage, prolonged fasting, differential response

Braun, E.J. 1998. The integrative control of fluid and electrolyte balance in birds. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 232.

As birds do not possess a urinary bladder, urine from the kidneys is carried by the ureters to the cloaca, the terminal segment of the gastrointestinal (GI) tract. The urine does not remain here, but is moved by a reverse peristalsis into the rectum. Here the composition of the urine is modified. Thus, the kidneys and GI tract must function in a co-ordinated manner in the maintenance of fluid electrolyte balance. We have devoted a significant effort to determining the nature of this integrative function. The reverse peristalsis that moves the urine into the rectum can be modulated by changes in the osmotic composition of the urine. In particular, if the urine becomes too concentrated, it is not moved into the rectum. Experimental manipulations show that changes in central (brain) osmolality do not change the cloacal/rectal motility; however, artificially changing (increasing) the urine osmolality has a marked effect on the motility of the lower GI tract (decreasing it). Our data suggest that: (1) the composition of the urine is sensed within the cloaca, and (2) the avian kidney should not produce a highly concentrated urine as this fluid is not moved into the rectum. This study was supported by the National Science Foundation.

Key words: kidney, hindgut, integration, osmoregulation, brain