F. Papi

The navigational feats of green sea turtles migrating from Ascension Island investigated by satellite telemetry

Previous tagging studies of the movements of green turtles (Chelonia mydas) nesting at Ascension Island have shown that they shuttle between this remote target in the Atlantic Ocean and their feeding grounds on the Brazilian coast, a distance of 2300 km or more. Since a knowledge of sea turtle migration routes might allow inferences on the still unknown navigational mechanisms of marine animals, we tracked the postnesting migration of six green turtle females from Ascension Island to Brazil. Five of them reached the proximity of the easternmost stretch of the Brazilian coast, covering 1777 to 2342 km in 33 to 47 days. Their courses were impressively similar for the first 1000 km, with three turtles tracked over different dates following indistinguishable paths for the first 300 km. Only the sixth turtle made some relatively short trips in different directions around Ascension. The tracks show that turtles (i) are able to maintain straight courses over long distances in the open sea; (ii) may perform exploratory movements in different directions; (iii) appropriately correct their course during the journey according to external information; and (iv) initially keep the same direction as the west–south–westerly flowing current, possibly guided by chemical cues.

The 7000-km oceanic journey of a leatherback turtle tracked by satellite

A leatherback turtle nesting on a KwaZulu-Natal beach was tracked by satellite for nearly 7000 km during internesting movements, rapid straight transfers and feeding-related movements in the Southern Ocean. Some parts of the track reveal the ability to maintain a straight course in the absence of cues deriving from the coastline or shallow bottoms. Swimming speed and diving behaviour varied in different segments of the journey. The value of satellite telemetry for planning conservation strategies is emphasized.

Olfactory navigation in birds

Many bird species rely on an osmotactic mechanism to find food sources even at a considerable distance. Pigeons also rely on local odours for homeward orientation, and they integrate those perceived during passive transportation with those at the release site. It is possible to design experiments in which birds are given false olfactory information, and predictions about the effects of this can be made and tested. Pigeons build up their olfactory map by associating wind-borne odours with the directions from which they come; this was shown by experiments which aimed at preventing, limiting or altering this association. Some objections have been made to this conclusion; namely that even anosmic pigeons are sometimes homeward oriented, that they may be demotivated in flying or disturbed in their general behaviour, and that olfactory cues may be only one component of pigeos navigational repertoire. The most recent experiments, however, confirm that pigeons derive directional information from atmospheric odouts. The lack of any knowledge about the chemical nature and distribution of the odorants which allow pigeons to navigate hinders progress in this area of research.

Pigeon navigation: Effects of wind deflection at home cage on homing behaviour

SummaryFrom fledging time up to the test releases, two groups of experimental pigeons were housed in two cubic cages supplied with deflectors which deviated the winds through to the inside approximately 70° clockwise (CW-birds) or counter-clockwise (CCW-birds). Test releases were made at 9.0, 23.5, and 105.3 km from the loft. With respect to that of control birds, the mean bearing of CW-birds was always deflected clockwise, and that of CCW-birds was always deflected counter-clockwise. Control birds performed better than CW-birds in homing from the first release site, and better than both experimental groups from the second release site.These results agree with the olfactory hypothesis of pigeon navigation (Papiet al., 1972).

Homing performances of inexperienced and directionally trained pigeons subjected to olfactory nerve section

SummaryPigeons not experienced in homing and subjected to olfactory nerve section are generally found to be unable to home from short distances. In nine successive releases from different localities at 3.3 to 11.8 km from the loft, 15 out of 19 experimental birds were lost as well as 2 out of 40 control birds.The homing capacity improves when the birds are released from familiar localities on a line along which they have been trained before undergoing nerve section, but they still perform very poorly in later releases from unfamiliar localities outside the training line. 11 experimental birds showed fairly good performances from a familiar locality on the training line at 43.4 km from the loft (10 returned within the same day of the release, at an average speed of 32 km/h). Only one of these birds was able to home within the same day in a later release in an unfamiliar locality outside the training line at 34.9 km from the loft. Five other birds of this group homed one or more days later, and the remaining five were lost.The initial orientation was poorer amongst the experimental birds. More of the inexperienced experimentals landed near the release point.As the experiments show that olfactory nerve section causes no disturbances in general behaviour and homing drive, it is concluded that olfaction plays an important and specific role in the homing mechanism of pigeons.

Examining the limits of flight and orientation performance: satellite tracking of brent geese migrating across the Greenland ice-cap

Brent geese, Branta bernicla hrota, were equipped with satellite transmitters on a spring stop-over site in Iceland. The brent geese deposit heavy fuel reserves for long-distance flights across the high Greenland ice-cap to breeding destinations in north Canada. Satellite tracking of brent geese on this journey serves the twofold purpose of testing specific predictions about: (i) size-dependent power constraints in bird flight (severe restrictions in climbing capacity with heavy payloads); and (ii) orientation constraints at northerly geographic and magnetic latitudes (different routes depending on which celestial or geomagnetic cues are used). Five individuals were successfully tracked to west Greenland, and they traversed the Greenland ice-cap where it reaches > 2500 m above sea level (ASI). Their climbing rates were exceedingly small, 0.01-0.06 m s-1, indicating critical size-dependent power limitations on flight. The movement up the ice slope was very slow, and the most plausible interpretation is that the geese paused frequently between partly anaerobic flights. The flight tracks were surprisingly irregular, although departure directions from Iceland and across Greenland were similar. The geese’s orientation is probably based on a combination of landmark piloting and a compass mechanism giving a constant geographic course irrespective of longitudinal time and geomagnetic declination (variation) differences along the route.

Island-finding ability of marine turtles

Green turtles (Chelonia mydas) swim from foraging grounds along the Brazilian coast to Ascension Island to nest, over 2200 km distant in the middle of the equatorial Atlantic. To test the hypothesis that turtles use wind-borne cues to locate Ascension Island we found turtles that had just completed nesting and then moved three individuals 50 km northwest (downwind) of the island and three individuals 50 km southeast (upwind). Their subsequent movements were tracked by satellite. Turtles released downwind returned to Ascension Island within 1, 2 and 4 days, respectively. By contrast, those released upwind had far more difficulty in relocating Ascension Island, two eventually returning after 10 and 27 days and the third heading back to Brazil after failing to find its way back to the island. These findings strongly support the hypothesis that wind-borne cues are used by turtles to locate Ascension Island.

Do geomagnetic disturbances of solar origin affect arterial blood pressure

Objective: Episodic reports suggest that geomagnetic disturbances of solar origin are associated with biological and clinical events, including increased arterial blood pressure (BP). We reassessed this aspect by relating solar activity levels to ambulatory BP measured in our out-patient population.Patients and methods: The ambulatory BP measurements of 447 consecutive untreated patients attending a hypertension out-patient clinic who did a monitoring for diagnostic purposes over 5 years were retrieved. The mean daytime, night-time and 24-h BP and heart rate values were related to the temporally corresponding geomagnetic index k-sum obtained by the nearest observatory. K-sum is a local measurement of the irregular disturbances of the geomagnetic field caused by solar particle radiation.Results: Significant to highly significant positive correlations were observed for k-sum with systolic (daytime and 24 h) and diastolic BP (daytime, night-time and 24 h), but not with heart rate. No correlations were found with the k-sum of 1 or 2 days before the monitorings. Multiple correlations which also included other potential confounding factors (date, age) confirmed a significant effect of k-sum on BP. Comparison made in season-matched subgroups of quiet and disturbed days (using three different criteria of definition), always showed significantly higher values in the disturbed days for all BP parameters except systolic night-time pressure. The difference between the quietest and the most disturbed days was of about 6 to 8 mm Hg for 24-h systolic and diastolic BP.Conclusion: These results are unlikely to be due to unrelated secular trends, but seem to reflect a real relation between magnetic field disturbances and BP.

Homing pigeons do extract directional information from olfactory stimuli

SummaryTwo groups of pigeons were kept from fledging time in two cages fully exposed to winds. From time to time, the cage containing experimentals was additionally exposed to an artificial air current coming from a specific direction and carrying a scent of benzaldehyde. When both groups were exposed to benzaldehyde scent during transportation and at the release site, the control birds flew homeward, whereas the experimentals oriented in the direction roughly opposite that from which they were used to perceiving the benzaldehyde at the loft. When benzaldehyde was not applied, experimental pigeons were homeward oriented like controls.

The effect of olfactory deprivation by nasal tubes upon homing behavior in pigeons

Summary1.As a test of the importance of olfaction to the navigational system of homing pigeons, a method of olfactory deprivation, the insertion of plastic tubes through the nostrils, has been employed. Birds wearing the tubes, and untreated controls, were singly released from two sites: a familiar one west of the loft, from which the birds had been released without tubes eight times previously, and an unfamiliar site south of the loft.2.From the unfamiliar site anosmatic birds showed drastically impaired homing ability, both in terms of vanishing bearings and homing success (only 6 of 33 homing on the day of release vs. 33 of 36 controls). From the familiar site, tube-equipped birds showed homing performance which was only marginally poorer than that of controls.3.The latter experiment shows that the effect of olfactory deprivation on homing is not a general behavioral influence on, for example, homing motivation, but is a consequence of the central importance of olfactory cues in determining home direction from unfamiliar territory. Anosmatic birds do home from familiar sites, presumably using an auxiliary pilotage mechanism relying on visual landmarks or other local cues.