Departure Directions Research Articles

Statistical study of the trajectories of the air masses flow in the Alpine area

As a part of our activity in the transboundary transport, this study examines a five years’ trajectory climatology interesting Northern Italy. Our analysis is twofold: firstly we examine the statistics of air masses arriving at an Alpine location (Brenner Pass) separating between rainy only trajectories and all trajectories, and, secondly, we study the climatology of trajectories, going out from the Po Valley. Trajectories are computed by means of a simple three-dimensional trajectory method using the wind data obtained by the analysis of the ECMWF. The distribution of the arrival (or departure) directions of the trajectories is presented and commented. The differences in the travel times for the different directions are presented as well. The vertical distribution of the trajectories is finally computed. The main results are discussed.

Caching Behavior in Free-Ranging White-Breasted Nuthatches: The Effects of Social Dominance

Using five mated pairs of free-ranging White-breasted Nuthatches Sitta carolinensis, I examined whether the social dominance of the male nuthatch over the female affects the caching behavior of each individual of the pair. I allowed each bird of a mated pair in five deciduous woodlots in central Ohio to scatterhoard 30 mealworms Tenebrio sp. For each caching trip, I recorded data on 10 variables describing cache site characteristics and social context. I compared niche overlap and niche breadth values to determine the degree of sex-specific caching behavior. Nuthatches typically cached food items in bark crevices on the trunks of large, highly rugose trees. Both male and female nuthatches selected trees for cache placement that had higher than average rugosity. Departure directions from the food source differed significantly between the sexes when the male cached first. Males used the trunks of trees as a substrate for caching significantly more often than did females. By utilizing a broader caching niche, the females may have reduced interference competition from their mate, and thus may have compensated for their socially subordinate status.

Orientation of tsetse flies to wind, within and outside host odour plumes in the field

Abstract Free‐flying wild tsetse flies (Glossina pallidipes Aust. and G. m. morsitans Westw.) were video recorded in Zimbabwe as they flew within an artificial host odour plume at 3, 7 or 15 m from the source, or in no odour, with and without a 0.75 m2 vertical, black visual target present aligned with the wind. With no visual target present, flights in odour were strongly biased upwind, and in the absence of odour strongly biased downwind. With the target present, between 16% and 40% of the upwind approaching flies responded visually as they passed the target, by circling it, in proportion to the proximity of the source (taken to be proportional to the mean odour concentration). Crosswind approaching flies (for whom the target will have been visible for some metres away) circled more frequently (34–56%), but without obvious correlation with the odour concentration. Circling flies also responded orthokinetically, by slowing down as they passed the target. The departure directions relative to the wind of flies leaving the target were significantly affected by the odour concentration. At 3 m they left the target in all directions, except possibly avoiding due upwind. At 7 m they left with an obliquely upwind bias, but at 15 m and also in no odour, they left with a strong crosswind bias.

Fecal Sac Dispersal by Prothonotary Warblers: Weatherhead's Hypothesis Re-Evaluated

Data on removal of fecal sacs by Prothonotary Warblers (Protonotaria citrea) were used to test Weatherhead's (1984) hypothesis that birds carrying fecal sacs away from the nest will vary their departure directions more widely than will birds not carrying fecal sacs in order to prevent attraction of predators. We recorded the departure direction of adults and whether or not they carried fecal sacs, as well as the distance flown to drop a fecal sac. Fecal sacs dropped over land were not carried significantly farther than those dropped over water. Although the distribution of directions flown with fecal sacs was significantly different than that of directions flown without fecal sacs, Prothonotary Warblers did not vary their departure direction more when carrying fecal sacs than when not carrying sacs. In fact, the distribution of trips without fecal sacs was more varied than trips with fecal sacs. Our results contradict the results of Weatherhead (1984), possibly because of differences in data analysis, and do not support his hypothesis of fecal sac dispersal.

The flight directionality of honeybees foraging on real and artificial inflorescences

An examination of the flight directionality, the change in direction between arrival and departure, of Apis mellifera (Apidae) workers foraging on artificial inflorescences and on inflorescences of Echinops sphaerocephalus L. (Compositae) is reported. Thirty-seven circular, artificial inflorescences, each with three feeding tubes separated by 120° located on the perimeter were used. At the beginning of each visit all tubes contained 2 ± 0.2 μL of 1.2 M sucrose solution. Bees locating the tubes would probe one or more of them, then depart to another artificial inflorescence and repeat the foraging sequence. Changes in flight directionality were generated during within-inflorescence locomotion and not after feeding had ceased. Directionalities of bees that circled a second time around these inflorescences were indistinguishable from bees departing the same locations prior to completing a single cycle. Hence, the directionality of bees visiting tubes in the sequence 1-2-3-1, 1-2-3-1-2, or 1-2-3-1-2-3 were indistinguishable from the directionality of bees visiting tubes in the sequence 1, 1-2, or 1-2-3, respectively. The direction faced by bees while probing the final tube or floret (last-faced direction) was most often the departure direction; thereafter, bees flew ahead to the nearest inflorescence. An energetic analysis of the artificial inflorescence study showed that directionality was independent of nectar uptake rates. The experiment using real inflorescences, some of which had been enriched with ca. 10 μL of 1.2 M sucrose solution, confirmed that directionality was generated during within-inflorescence locomotion and that the last-faced directon was the most frequent departure direction; furthermore, changes between the last-faced and departure directions were independent of nectar uptake. Evident in the search pattern of honeybees were the following: (i) a forward-moving tendency while on inflorescences, (ii) a departure decision, (iii) departure in the last-faced direction, and (iv) minimum deviation from the last-faced direction when flying directly to the next inflorescence. Although bees tend to move in a forward-facing direction during all movement phases, the floral architecture facilitates or induces turning. The extent of the turn is limited by the bees decision to depart. It is concluded that directionality is an epiphenomenon resulting from interactions among floral architecture, bee locomotion, floral nectar content, and the bee's departure decision. Memory of the arrival direction is not required.

Aggregative mechanisms and behavior in ring-billed gulls departing from a colony

Departures of ring-billed gulls (Larus delawarensis) from a breeding colony were significantly clumped in time and space. Mean departure directions did not correlate among successive days, but were highly correlated with wind direction. Most gulls circling about the colony did not depart. Gulls that did depart typically flew directly away from the colony and approximately half emitted distinctive "contact" calls. Significantly more gulls departed when others were soaring on nearby thermals than at other comparable times. Playback experiments showed that contact calls and calls from thermal flocks attracted other gulls. A causal model of flock formation, derived from the assumption that temporal clumping arises from social facilitation superimposed upon random departure times, was supported by (i) random fly-up times by nondeparting gulls, (ii) demonstrated attractiveness of contact calls, (iii) characteristically direct flight paths of departing gulls, and (iv) by simulations of departing gulls. Social attraction, temporal and spatial grouping, wind, and visual contact between successively departing birds all appear to facilitate aggregation within localized regions of the habitat.

WINTER ROOSTING AND FEEDING BEHAVIOUR OF PIED WAGTAILS MOTACZLLA ALBA NEAR OXFORD, ENGLAND

SummaryThis study presents data on the roosting and feeding behaviour of Pied Wagtails around Oxford, England. During the winter of 1977–78, from two to 1200 wagtails roosted in a Phragmites reed‐bed. Use of this roost was greatest during mild, windless weather and the birds apparently used alternate roosts during harsh weather. Movement between roosts sometimes occurred between sunset and sunrise. Morning ‘departure group’ size, number leaving per unit time and diversity of departure directions increased with roost size. Wagtails quickly left the vicinity in the morning. In the afternoon, they joined one or more pre‐roost gatherings before entering the roost for the night. Behaviour upon arrival at the roost was variable: birds might enter the reeds quickly or circle in large groups before landing. Aerial revolutions and generally ‘restless’ behaviour often accompanied increases in roost size.Wagtail feeding rates varied significantly between and within habitats. Number of wagtails feeding on the flooded Port Meadow, located 2–3 km south of the main roost, varied from about five to over 60 on different days; these numbers were not correlated with feeding rates. In contrast, the number of birds feeding at a sewage farm was nearly constant all winter. Some wagtails show high fidelity to feeding areas but others do not. Five short‐term food supplementation experiments indicated that wagtails knowledgeable about a dense food source are not followed in the morning by naive birds.Results of this study are discussed in relation to the predation, physiology and information centre hypotheses that have been suggested to explain communal roosting in birds. I conclude that the communal roosting system of Pied Wagtails has physiological and anti‐predator functions. Wagtails appear to choose certain roosts because of the protection that they provide from adverse climate and predation.

RECENT EXPERIMENTS ON BIRD ORIENTATION

Summary.Pigeons raised in open aviaries show homeward orientation when released 100 or 150 km. away from their home aviary. Some of them (15–20%) actually return.When palisades are placed around the aviaries orientation vanishes. The palisades allow the birds free sight of the sky except for a zone of an elevation of 3° above horizon.Orientation is absent also in pigeons raised in an aviary giving view of a broad sector to the north, i.e. the direction opposite to release. These experiments are being continued.Homing pigeons were subjected to an artificial light/dark change (period 24 hours). If the artificial cycle was out of phase with the natural day/night cycle, the “internal clock” was shifted within three to four days as shown by directional responses.Basically the same deviations are shown by “shifted” pigeons taken away from home and released. What appears to be influenced by shifting is a directional response which must necessarily rest upon a previous determination of position relative to home. This preceding part of the whole orientation performance appears to be unaffected.Orientation is influenced by spatial factors, or factors related to space, of unknown nature. The observed phenomena may be tentatively subdivided into variations due to direction, site of release place, site of loft, and region.Among weather conditions, cloud cover has a significant influence upon homing orientation. Top‐class homing flights are less frequent with overcast.Homing ability is subject to an annual fluctuation. Homing is best in August and poorest in January. Parallelity to temperature is obvious throughout the year. Correlation between particular releases and temperatures prevailing at the particular occasions exists only in autumn and winter but not during the rest of the year.A correlation has also been found with interdiurnal barometric change. This correlation is scarcely perceptible at surface level, but significant at the 500 and 200‐mb. level. This correlation concerns homing performance as well as correctness of departure directions, but not scatter of departures.So far no cross relations can be established between results attained with the different ways of approach.It is thought that homing ability as shown by the domestic pigeon continues to be a problem of ornithological interest. It is assumed the same ability is possessed by wild species.