Emlen Funnels Research Articles

The dusk orientation and the influence of successive tests on pied flycatchers (Ficedula hypoleuca) tested in Emlen funnels

Pied flycatchers were tested twice at sunset under a clear sky, a clear sky with moon, and under artificial overcast conditions. The mean spring direction was W‐NW, with a higher westward bias than in previous tests performed in complete darkness. The activity of single tests was high but their directionality was low, with an inverse correlation between activity and directionality. Under clear skies (with or without moon) the distribution of birds performing a test for the first or second time was not different, with high consistency of individual birds, while in overcast conditions second tests shifted southwards, seemingly a phototactic reaction. Under clear skies (with and without moon), in the second test individual vector lengths increased and there was no correlation between individual activity and vector value, indicating an improvement of the perform ance; in contrast, in second overcast tests vectors tended to decrease and the negative correlation activity/vector was significant. So, although the mean direction was not different from the clear sky, the individual performance was worse in overcast conditions, probably due to a decrease in motivation to migrate during prolonged overcast conditions.

Migratory Orientation of Blackcaps (Sylvia atricapilla): Population‐specific Shifts of Direction during the Autumn

AbstractThe population‐specific orientation of two groups of blackcaps (Sylvia atricapilla), one from southwest Germany, the other from easternmost Austria, was studied outdoors in Emlen funnels. We investigated whether a seasonal shift in the migratory direction — as expected for the Austrian birds from ringing recoveries — occurs under experimental conditions and in a seasonally constant magnetic field. The West German birds, for which no shift was expected, oriented southwest during the entire season. The Austrian birds oriented southeast in October and southsouthwest in November. The clockwise shift by about 60° occurred within a 10‐day period.The results indicate that in this species seasonal changes of migratory direction are probably based on an endogenous program, occur without the birds actually migrating and are independent of changes in the magnetic field. Our results provide further evidence that directional shifts in Sylvia warblers may be controlled by a different mechanism than in pied flycatchers (Ficedula hypoleuca).

Skylight Polarization Patterns and the Orientation of Migratory Birds

ABSTRACT Patterns of polarized light present in the clear dusk sky provide directional information relevant to the orientation behaviour of migratory birds. Experiments performed with white-throated sparrows (Zonotrichia albicollis) and American tree sparrows (Spizella arborea), North American night migrants, examined migratory orientation between the time of sunset and the first appearance of stars under several manipulations of skylight polarization patterns. Under clear skies, birds tested in Emlen funnel orientation cages oriented their hopping basically parallel to the E-vector of polarized light, with a bias towards the brightest part of the sky (sunset direction). Under solid, thick overcast conditions (no polarized light from the natural sky), birds showed axially bimodal hopping orientation parallel to an imposed E-vector. When birds were tested in cages covered with depolarizing material under a clear sky, their hopping orientation was seasonally appropriate and indistinguishable from controls viewing an unaltered clear sky. Skylight polarization patterns are not necessary for the occurrence of migratory orientation, but birds respond strongly to manipulations of the E-vector direction. The results reported here support the hypothesis that the relevant stimulus is the E-vector orientation rather than other parameters of skylight, e.g. intensity or colour patterns, degree of polarization. It appears that these night migrants are using skylight polarization at dusk as one of a set of multiple compass capabilities. Because of the necessarily artificial nature of the polarized light stimuli used in the experimental manipulations, it has not been possible to establish the relationship between this orientation cue and other known mechanisms (magnetic, sun and star compasses).

Orientational Responses To Different Light Stimuli By Adult and Young Sedge Warbler (Acrocephalus Schoenobaenus) During Autumn Migration: a Funnel Technique Study

In a North-eastern area of the Po Valley (Northern Italy), tests on the orientation pattern of sedge warblers during autumn migration were carried out for two consecutive years. It was found that the sedge warblers tested in Emlen funnel cages orientate in a southerly direction, in accordance with the expected migratory line during postnuptial migration. The recorded mean directions are revealed as very similar, at least during the beginning of the night, in both the adults and the young birds. Nevertheless, the orientation of the latter seems to be more disturbed by natural or artificial light sources such as the sunrise, the moonlight or the horizon glow present in the area, and towards which they seem to show a tactic component. Owing to the fact that the sunlight at the point of sunset is the only light stimulus which never induced a phototactic response in the juvenile birds, it is possible to presume that the sunset point bearing may be one of the orientational cues used by sedge warblers to establish the course of its migratory flight.

Additional Evidence of Nocturnal Migration by Yellow-Rumped Warblers in Winter

Migration is a response to changing environmental conditions (Gauthreaux 1982). Migratory behavior spans a continuum from highly fixed behavior (obligate migration) to very flexible behavior (facultative migration). Whereas facultative migration occurs in response to deteriorating environmental conditions, obligate migration appears to be fundamentally a result of an endogenous, circannual program (see Gwinner 1986 for a recent review). Even obligate migrations, however, are not performed entirely without integration of environmental information. For example, migrants make daily decisions to migrate or not to migrate based upon environmental factors such as weather conditions, food and water availability at stopover sites, and competition (e.g., Rappole and Warner 1976, Richardson 1978, Mehlum 1983, Biebach 1985, Gwinner 1986, Biebach et al. 1986). The degree to which migratory behavior is subject to environmental influence appears to be quite variable (Terrill and Ohmart 1984). There is evidence that at least some species of annual, migrant passerines facultatively extend migration after the fall migratory period if environmental conditions become unfavorable for overwinter survival at a particular locality (Perdeck 1964, Niles et al. 1969, Moreau 1972, Lack 1983; Terrill and Ohmart 1984; Terrill 1987, in press). Presumably, the ability to perform facultative migrations enables these birds to respond to relatively unpredictable winter environments by migrating in an appropriate direction if conditions necessitate it. Patterns of migration and distribution of Yellowrumped Warblers (Dendroica coronata) indicate that they switch from an obligate phase to a facultative phase over the course of fall migration (Terrill and Ohmart 1984). Winter populations shift southward if conditions become unusually severe. When placed in Emlen funnels (Emlen and Emlen 1966), Yellowrumped Warblers showed southerly nocturnal orientation into early January (after which no birds were tested). While the orientation data support the hypothesis that winter movements like fall movements are nocturnal, the evidence is indirect. Here we present direct evidence that winter movements by Yellow-rumped Warblers are in fact noctur' Received 15 April 1987. Final acceptance 27 August 1987. 2 Present address: 208 Junius St., Thomasville, GA 31792. SHORT COMMUNICATIONS 261

Richtungsbevorzugungen von Mönchsgrasmücken (Sylvia atricapilla) während der Herbstzugunruhe. Vergleich zweier Populationen mit verschiedenen Zugrichtungen

AbstractDirectional Preferences of Autumnal Migratory Restlessness in Two Populations of Blackcaps (Sylvia atricapilla) with Different Migratory DirectionsThe directional preferences in the orientation behavior of blackcaps, Sylvia atricapilla, were investigated. Two populations on different sides of the migratory divide were studied; one which flies in a SE direction in autumn and one which flies in a SW direction. The populations were from Lake Constance in the F.R.G. and Lake Neusiedl in Austria. Directional preference during fall migratory restlessness was determined by using Emlen funnels. The birds were hand‐raised from the nestling phase on under identical conditions.The results demonstrated significant differences between the populations in the autumnal directional preferences. For SW migrants it was 240.7° and for SE migrants 185.0°. One can conclude from these results that there are population‐specific differences in the innate directional preferences of fall migratory restlessness.A number of possibilities are discussed as causes for the extreme westward orientation of the birds from Lake Constance: The WSW orientation of the Alps could be genetically programmed into the pattern of migration. It could have been the result of a compensation for the transport from Lake Constance to Lake Neusiedl and therefore explained by goal area navigation. Recently, there have been many reports of German blackcaps wintering in Holland, England and Ireland. It is possible that a number of the experimental birds had already chosen this direction and with their WNW preference, the overall preference is shifted westward.

Age-Dependent Variability in the Migratory Orientation of the Savannah Sparrow (Passerculus sandwichensis)

Age-Dependent Variability in the Migratory Orientation of the Savannah Sparrow (Passerculus sandwichensis)

Age-differential homing tendencies in displaced bank voles, Clethrionomys glareolus

Escape movements of three different age classes of encaged bank voles, Clethrionomys glareolus Schreber, were studied in modified Emlen funnels. While there was a concentration about the mean direction in the adult and overwintered subadult groups (i.e. homing) when tested in darkness, no such concentration was found when testing yearling subadult bank voles. When tested in the light no concentration about the mean direction occurred in any age class. The differences in homing tendencies between the tested age classes are consistent with known differences in their behaviour. While adults and overwintered subadults about to become adults have fixed home ranges, yearling subadults generally do not have well-defined activity areas and hence lack a homing goal. In the light, all animals behaved as if running for the nearest cover rather than in any particular direction.

Sunset and the orientation of a nocturnal bird migrant: A mirror experiment

If savannah sparrows, (Passerculus sandwichensis), a North American night migrant, select a migratory heading based upon the setting sun, a shift in the position of that cue should produce a predictable shift in the migrant's nocturnal orientation. I tested this hypothesis by shifting the sunst position with mirrors and by recording the bird's orientation in Emlen funnels. The control group displayed directionality appropriate for spring migration (ā=342°). The mean heading of experimentals (ā=272°), which were exposed to a cue-shifted situation, was in the expected westerly direction relative to the control mean (P<0.05, V-test). The setting sun appears to be a sufficient source of directional information for this avian migrant.

Magnetic Orientation in Night-Migrating Passerines

Initially the intention of these experiments was to repeat the investigations of the Frankfurt group (e.g. Wiltschko 1968) using another kind of cage design. Could magnetic orientation be demonstrated in a small Emlen funnel only 29 cm in diameter and by application of a horizontal field produced by bar magnets? In the meantime, the papers of Wiltschko and Wiltschko (1975a, 1975b, 1976a, 1976b) appeared, concerning the dominance and/or primacy of magnetic orientation over stellar orientation. Thus an additional and very important question became whether the findings and conclusions of the Wiltschkos could be repeated and confirmed by the funnel experiments, in which conflicting information from stellar and magnetic cues was presented to the birds.