Olfaction in bird dogs during hunting.

The ability to catch scent continuously while running, which may be an essential skill for many animals of prey, requires that ambient air flows inward through the nose also during expiration. In this study on bird dogs, the direction of air flow was detected by measuring the temperature in the air inside the nostril. While resting, nose ventilation was synchronous with lung ventilation. While searching for ground scent, the dog was sniffing at a frequency of up to 200 s-1, a strategy which may create turbulence in the nasal passages and thereby enhance transport of scent molecules to the receptors in the ethmoidal cavity. When the bird dog was searching for game while running with its head high against the wind, it maintained a continuous inward air stream through the nose for up to 40s spanning at least 30 respiratory cycles. We suggest that expiratory gas flowing at high velocity from the trachea to the mouth cavity creates a lower pressure than in the nose thus causing an inward air stream through the nose during expiration by a Bernoulli effect.

Behaviour of dogs during olfactory tracking.

The ability to detect the direction of a track is of vital importance to animals of prey and is retained in many modern breeds of dogs. To study this ability, four trained German shepherd tracking dogs, equipped with head microphones to transmit sniffing activity, were video-monitored after being brought at right angles to a track where the position of each footprint was known. Three phases could be recognized in the dogs' behaviour: (1) an initial searching phase, during which the dog tried to find the track, (2) a deciding phase, during which it tried to determine the direction of the track and (3) a tracking phase, in which it followed the track. During ten tests on 20-min-old tracks on grass, and ten tests on 3-min-old tracks on concrete, the dogs always followed the track in the correct direction (i.e. in the direction the track was leading). During the deciding phase the dogs moved at half the speed and their periods of sniffing lasted three times as long as during the other two phases. The deciding phase lasted 3-5 s, while the dogs sniffed at 2-5 footprints. The dogs' ability to determine track direction in this time must rely on accurate methods of sampling air and a remarkable sensitivity for certain substances.

How do dogs determine the direction of tracks?

Two professional tracking dogs were brought in at right angles to 50-m-long tracks to try to identify the clues that the dogs used to determine the direction of the tracks. When the dogs were tested on tracks laid by a walking man, they took the direction that the track-maker had moved significantly more often than predicted by random choice regardless of whether the person had moved forwards or backwards. When tested on tracks laid by bicycling on grass or asphalt, the choice of direction was not significantly different from random, even though the dogs were always rewarded when making correct choices. When four leather strips were tied to the back tyre of the bicycle before laying the track, the one dog tested took the correct direction significantly more often than predicted by random choice. When the leather strips were smeared with sausage before laying the tracks, the dog took the wrong direction more often than predicted by random choice. However, when rewarded for making correct choices, the dog learned to choose the direction in which the bicycle had actually moved. We suggest that our dogs determined the direction of tracks by comparing the scents of consecutive prints and following the prints in the direction of increasing intensity.

Physiological aspects of freezing behaviour in willow ptarmigan hens.

When threatened, wild willow ptarmigan (Lagopus lagopus lagopus) hens displayed freezing behaviour, i.e. motionless, crouched with head down and eyes open. But while non-incubating hens showed increased heart (HR) (from 229 +/- 18 to 254 +/- 33 beats min-1) and ventilation rates (VR) (from 25 +/- 2 to 31 +/- 4 breaths min-1), incubating hens showed bradycardia (from 208 +/- 40 to 102 +/- 13 beats min-1) and reduced VR (from 25 +/- 2 to 10 +/- 2 breaths min-1), which could be maintained for as long as 20 min. The bradycardia response became stronger as hatching approached. The bradycardia period was interspersed by short bursts of tachycardia and hyperventilation which presumably supplied oxygen to blood and muscles. The bradycardia period was typically followed by a period of increased HR (276 +/- 104 beats min-1) and VR (32 +/- 3 breaths min-1). Atropine abolished the bradycardia response, which was thus apparently due to parasympathetic stimulation. The bradycardia response observed in incubating ptarmigan hens, during forced diving of birds and mammals and during death feigning in other animals are all examples of how emotional stimuli trigger a basic bradycardia reflex.

The development of homeothermy in common eider ducklings (Somateria mollissima).

Oxygen consumption (VO2), body temperature (TB) and electric muscle activity (EMG) were measured at varying ambient temperatures (TA) in common eider ducklings from the eggs pipped to 1 day after hatching. Eggs at pipping and ducklings still wet from hatching doubled their VO2 at TA = 2-4 degrees C compared with TA = 27 degrees C, but were unable to maintain constant TB. Increased EMG activity was recorded from ducklings 30 min after hatching. Artificially dried 1-h-old ducklings maintained normal TB (39.0-40.5) for at least 90 min at TA = 2 degrees C. Ducklings older than 24 h maintained homeothermy even when the pelt was artificially wetted. Oxygen consumption at thermoneutrality increased about 50% from hatching to 12 h of age. The specific thermal conductance of ducklings at different ages indicates that the youngest ducklings maintain homeothermy by having a cold periphery in addition to pelt insulation and increased VO2, while ducklings older than 12 h rely on pelt insulation and increased VO2 only.

Oxidative capacity of tissues contributing to thermogenesis in eider (Somateria mollissima) ducklings: changes associated with hatching.

1. The development of liver and skeletal muscle oxidative capacities during hatching of the common eider (Somateria mollissima) in the Arctic has been investigated by monitoring tissue cytochrome c oxidase activity. 2. The specific activity of the liver enzyme did not change as the embryo underwent hatching, nor during subsequent growth of the duckling into adulthood. 3. Thigh muscle enzyme specific activity increased by a factor of 3.4 during the 24 h prehatching period, remained elevated for at least 48 h after hatching, and then returned to the embryonic (-24 h) level in adults. 4. Histochemically visualized NADH-tetrazolium reductase of a typical red thigh muscle, M. vastus lateralis, showed a distinct increase in activity as the hatching process progressed to completion. 5. Electron microscopy of sectioned M. vastus lateralis revealed a dramatic increase in the density of the myofibrillar structure (number of mitochondrial profiles per unit area), and in the surface area of mitochondrial crista membranes in the course of the 48 h interval from 1 day prehatching to 1 day after hatching. 6. The significance of these changes for the scaling of thermoregulatory heat generation in the newly hatched eider duckling is discussed.

Vitamin C deficiency in growing willow ptarmigan (Lagopus lagopus lagopus).

Willow ptarmigan chicks raised on a diet containing 265 mg ascorbic acid/kg develop scury-like symptoms and die by 4 weeks of age. If blueberry plants are given as an ad libitum supplement to this diet, the malady is prevented. We have described the clinical, pathological and histological changes which accompany this malnutrition and conclude that they are in accord with the description of scurvy in guinea pig and man. Biochemical determination of ascorbic acid synthesis in the kidney of ptarmigan chicks indicated a rate of synthesis five times that found in livers of growing white rats. Blueberry plants and many other plants found in the natural diet of ptarmigan chicks contain 2,000 to 5,000 mg ascorbic acid/kg dry weight. Feeding experiments showed that the pathological signs were avoided and that already afflicted chicks recovered if the vitamin C content of the diet was raised to 750 mg/kg dry weight of food. Since the food intake of the chicks was 5 to 8 g/day the daily requirement of external vitamin C is about 150 mg/kg body weight. To our knowledge this is the first example of an animal which, while producing vitamin C itself, requires substantial amounts of external vitamin C to survive.

Tachycardia during egg-hypothermia in incubating ptarmigan (Lagopus lagopus).

Incubating birds regulate the egg temperature by varying their posture and the distance between eggs and brood patch. In the present study, we show that this homeostatic process is further assisted by varying the brood patch blood flow according to the temperature of the eggs. When female ptarmigan resume incubation of cooled eggs (e.g. after a period of foraging), they immediately develop pronounced tachycardia (4 times noraml in wild, 2-3 times in captive birds). Tachycardia is maintained, although at decreasing intensity, until the eggs have obtained normal temperature. The eggs are heated 30 to 50% slower in females where tachycardia is inhibited by a beta-receptor blocking agent.

Blood flow, calcium deposition and heat loss in reindeer antlers.

Antler blood flow was studied in a 2 year old male reindeer during the last half of the antler growth period using an electromagnetic flow probe chronically implanted around the superficial temporal artery. Arteriovenous (a-v) differences of calcium were measured on antler blood. The blood flow increased from 60--90 ml/min when the antler was half-grown to 100--120 ml/min when fully developed. Subsequently a reduction was observed towards shedding. Positive a-v plasma calcium differences (on average 0.2 mM) were recorded during the period of active growth. Two bulls maintained positive a-v calcium differences after a 48 hour starvation period, in spite of reduced arterial calcium concentrations. Exercise to near exhaustion caused a 2 degrees C rise in the rectal temperature. Antler blood flow was decreased immediately after exercise and returned to pre-exercise values usually within 5--10 min. Since no overshoot in antler blood flow was recorded during the hyperthermia it is concluded that variations in blood perfusion of the antlers are without importance in the defence against hyperthermia during and after exercise.

Gas deposition by counter-current multiplication in the eel swim-bladder: experimental verification of a mathematical model.

1. Blood pO2 along the rete of eel has been investigated with a microelectrode, the swim-bladder gas being replaced by air. 2. When the eel does not secrete gas, the pO2 profile is flat, whereas in actively secreting eel the pO2, along the rete has a maximum of approximately 1 atm near the bladder pole of the rete. 3. The findings confirm predictions of a mathematical model for counter current multiplication in the swim-bladder.

The effect of plasma proteins on the capillary permeability in the rete mirabile of the eel (Anguilla vulgaris L.).

Measurements of transcapillary exchange of high-molecular dextrans, K+ and THO in the rete mirabile of the eel (Anguilla vulgaris L.) have been made under steady-state conditions while varying the amounts of plasma proteins in the perfusates. When the perfusates contained 20% or less horse serum the permeabilities of D-75 000, K% and THO increased significantly. The effect on the K+ permeability was irreversible while that on D-75 000 and THO was not. The permeability was unaffected when the perfusate contained 30% serum or more. Adding 1.3 g/100 ml bovine albumin to the perfusate maintained the D-75 000 and THO permeabilities unchanged while that of K+ appeared to increase. At an albumin content of 0.33 g/100 ml the effect was similar to that produced by low serum perfusates. Our main conclusion is that lack of the albumin fraction of the plasma proteins reversibly increases the intercellular pore area and irreversibly changes the K+ permeability of the cell membrane.

The effect of serotonin and transcapillary pressure on the capillary permeability in the rete mirabile of the eel (Anguilla vulgaris l.).

Measurements of transcapillary exchange of high-molecular dextrans, K+ and THO in the rete mirabile of eel (Anguilla vulgaris L.) have been made under steady-state conditions while the transcapillary pressure was varied and pharmaca added to the perfusates. Raising the transcapillary input pressure increased the exchange of dextrans and K+ but lowered that of THO. Histamine and ouabain had no effect on the transcapillary exchange of the test molecules. The highest dose (100 mug/ml) of serotonin reversibly increased the capillary permeability of D-75 000, K+ and THO while the medium dose (50 mug/ml) only raised the transcapillary exchange of K+ and THO. The lowest dose (10 mug/ml) had no permeability effect. Our main conclusion is that serotonin reversibly increases the area of the intercellular pores by affecting the capillary wall directly.

Regulation and grinding ability of grit in the gizzard of Norwegian willow ptarmigan (Lagopus lagopus).

Fluctuations in grit composition in the gizzards of willow ptarmigans and the grinding ability of various grit assortments from wild ptarmigans were examined. We confirmed reports of other investigators that larger, fewer and rounder stones were present in the winter than in the autumn. Experiments showed that ptarmigans prefer stones with diameters between 2-5 mm. Birds on a constant diet maintained a constant stone intake throughout the year. The composition of gizzard grit was influenced by the availability of stones as well as of the type of food the ptarmigans ate. Using an artificial gizzard, grit from birds shot during the autumn was found to be a more efficient grinding material than grit from winter birds. We suggest that other functions than grinding, such as supplying minerals, may be equally important functions of the grit.

The permeability of fish gills with comments on the osmotic behaviour of cellular membranes.

The permeability of eel gills to ions, lipid-soluble and -insoluble substances has been measured under steady-state conditions. The results obtained support the multi-pathway model for transcapillary transport (Stray-Pedersen and Steen 1975). The gills are 25 times more permeable to THO than to Na+ or K+. Metabolic inhibitors do not affect the transfer of substances across the gills. Exposure to EDTA or MS-222 changes the permeability properties to resemble those of an aquous barrier. The gills are 10 times less water permeable than the capillaries of the rete mirabile.

The capillary permeability of the rete mirabile of the eel, Anguilla vulgaris L.

Direct measurements of transcapillary exchange during steady-state conditions have been performed in the rete mirabile of the eel. The capillaries were found to be more than 30 times as permeable to THO (PTHO = 33.2 times 10(-5) cm sec-1), ethanol and antipyrine than to K+. The mutual relationship of the permeabilities for K+, Na+, urea and sucrose were similar to that between the corresponding free diffusion coefficients in water. The permeability characteristics did not change when the perfusate contained metabolic inhibitors. Additional of 1 mM/l of albumin lead to a significant transcapillary osmotic flow. NaCl, urea and sucrose, however, did not cause osmotic flow. Based on the quantitative values for permeability and volume flow the capillary pores should be about 1300 A and have a frequency of 1.3 times 10(6) per cm2 of the capillary surface, occupying an area of about 0.1% of the total area. The results obtained in the present investigation raise questions as to the validity of the Pappenheimer single-pore theory for transcapillary transport as well as to the fine structure of the capillary pores. As an alternative to Pappenheimer's theory a multi-pathway model is proposed in order to explain transcapillary transport.