I have established the fowl as a model for studies of thermoregulatory capacities in avian species using comparative studies of the commercial strains with the unique desert-origin Bedouin Fowl. I have shown that under extreme environmental conditions, Bedouin fowls express their natural (genetic) adaptations and effectively regulate their physiological homeostasis. Including reproductive mechanisms are an essential component in the physiological performance of birds under stressful conditions.. This model comparative system was tested recently at the cellular and molecular level in relation to the heat shock response. The rock pigeon was found to be the most heat resistant bird so far studied. In collaboration with the late Prof. Jacob Marder we have shown that heat acclimated pigeons can regulate a normal body temperature under extreme heat of up to 60oC using its unique capacity for water evaporation through the skin. This capacity enables the rock pigeon to breed and grow nestlings, while maintaining metabolic rate, acid base status and brain temperature. In a long series of studies, we made a major contribution by showing that birds could employ an effective mechanism of brain cooling under stressful conditions of heat and dehydration. This capacity is achieved by cooling the arterial blood flowing to the brain in a vascular heat exchange – the rete ophtalmicum. In a further step, this capacity was used as an index for the ontogenetic development temperature regulation in altricial and precocial species.
Conservation of wetland and ecophysiology of fish-eating birds
In the recent years, my team has focused on the long-lasting, intensive conflict between fishermen and the conservation of the deteriorating wetland habitats for fish-eating birds. To find a solution to this conflict, the strategy adopted was to study thoroughly the biology of the species concerned, with emphasis on their energy requirements, foraging and feeding behaviour and other physiological capacities. These studies constructed a scientific basis for the future management of the problems. Such was the conclusion that migrating pelicans must stop-over for feeding in Israel on route to Africa and consequently, the implementation of the safe feeding sites offered for migrating white pelicans. The current studies of the wintering great cormorant and the resident pygmy cormorant, a bird on the verge of global extinction reveals for the first time their different energetic requirements and prey preference, their underwater foraging performance and their hydromechanics of diving, with far reaching ecological implications for their management and protection. Already, these studies are affecting the routine behaviour of the fishermen and wild killing by fishermen is reduced to a great extent.
Ecolphysiology of feeding in mammals and passerine birds
In a series of studies we focused on the physiology of the Egyptian fruit bat that revealed its adaptations to the low protein content of its diet and its capacity to effectively regulate its metabolism and body temperature under heat exposure and dehydration. In the next stage we focused on the nitrogen metabolism of passerine birds in an attempt to evaluate their minimal nitrogen requirements (MNR), total endogenous nitrogen loss (TENL), and the effect of protein and water intake on their nitrogenous waste composition. Physiologists characterize birds as uricotelic because they excrete most of their nitrogenous “waste” products as uric acid. We are testing the possibility that this substance is something else than just a waste and study an alternative physiological role of uric acid, hypothesizing that uric acid is not only a waste product, but also a powerful antioxidant in passerine birds. Recently, we were interested in the ecophysiology of rodents and birds in relation to plant secondary metabolites. With evidence accumulating that shows birds absorb a significant fraction of water-soluble sugars via the passive, paracellular pathway (as opposed to using the transporter-mediated mechanisms that mammals rely on heavily), we wondered if this would expose them to increased levels of plant-derived, water-soluble toxins relative to their mammalian counterparts. Water-soluble toxins are a major class of plant secondary metabolites, and animals that consume a wide variety of plant materials are known to ingest them. To test our idea, we measured paracellular absorption of water-soluble carbohydrate probes in the gastrointestinal tracts of four fruit-eating species (two avian and two mammalian). In doing so, we found that the birds (both passerines) passively absorbed significantly more of the water-soluble compound than the mammals (both rodents).
Ecophysiology of land-snails
In a long series of studies, it was shown that the distribution patterns of land snails in Israel are mainly determined by the aridity gradient (precipitation and temperature) from north to south and from west to east. We revealed a suite of physiological, morphological and behavioural adaptations that work in concert to achieve water balance. These adaptations were shown to occur at all levels of biological complexities and life histories (inetr- and intraspecific differences, differences in life style (bush, rock or soil dwelling), according to the specific microhabitat, and may be of phylogenetic and genetic origin. I was recently studying the possible involvement of stress proteins in the annual cycle of aestivation and activity of desert and non-desert species.
