ALBERT

Description / Table of Contents: Summary 1. A possible correlation between the vocalizations of three native reed warbler species and their respective habitat types was investigated. The physical aspects regarding sound transmission in these habitats were investigated and compared with the basic frequencies in the territorial songs of the three Acrocephalus warblers. It is concluded that habitat acoustics play an important role in the evolution of vocalizations used in long distance communication. 2. The songs of the three species were analyzed to find the preferred frequency, the frequency range and sound type:A. schoenobaenus: h3 (1,97 kHz) — f5 (5,58 kHz),A. scirpaceus: c3 (1,04 kHz) — a4 (3,52 kHz),A. arundinaceus: g2 (0,78 kHz) — h4 (3,96 kHz). 3. The acoustic properties of each habitat were investigated by sound propagation tests (broadcasting constant sinusoidal sound waves). The sound attenuation was measured from three distances and with nine different loudspeaker microphone combinations each (see fig. 1). Single measurements were made in the habitats ofA. scirpaceus andA. arundinaceus. Two different measurements (one early and one late in the season) were made in the habitat ofA. schoenobeanus. Data from all four measurements permitted the following generalizations: a) attenuation is frequency dependent b) attenuation increases strongly above 5 kHz c) there is a negative correlation between attenuation and height above water or ground d) positions of loudspeaker and microphone could be interchanged without altering the attenuation index. 4. Special consideration was given to short-term amplitude modulations, because of their effects on sound localization. The following generalizations are possible: amplitude varies depending a) on height above water, and b) on wind, and c) on distance. However, no definite statements are possible in regard to these three points. d) It can be said with certainty that amplitude modulation is dependend on frequency. The former increases continuously beginning at 1 kHz; below 1 kHz there is almost no amplitude modulation. 5. The possible reasons, especially for the different attenuation effects, were considered. Reflection of sound from the water surface was important. There is a difference in time of arrival between the lineal and reflected sound waves (see fig. 9). In some circumstances this may result in extinction and in others in amplification. 6. Penetration of the vocalization of the three reed warbler species in their species-specific and, theoretically, in the other habitats was investigated. a) A. schoenobaenus: Differences in sound attenuation between spring (relatively small attenuation) and late summer (more pronounced attenuation) were noted. These were due to thicker vegetation and parching. It was noted that attenuation at the top of the vegetation in the specific habitat ofA. schoenobaenus was comparatively higher than in the other habitats due to the lesser heights of plants (maximally 2 m) here. Sound attenuation was negatively correlated with height, the species is tending to get away from the ground by frequent song flights. This typical behaviour permits the species to utilize high frequencies. TheA. schoenobaenus has not developed any preferred singing posts within the vegetation. b) A. scirpaceus: The acoustically optimal singing posts of this species should be the tops of the vegetation. Singing posts are, however, preferred in the middle of the vegetation. Whether or not this (acoustical) disadvantage is compensated by especially good penetration of the frequencies at 1,6 and 2 kHz, could not be determined with certainty. It is possible that there is a correlation between the strong attenuation of its song and the small territories and also the clumped distribution of territories. c) A. arundinaceus: It is noteworthy that there is good penetration of the lower frequencies between 0,4 to 1 kHz in the species-specific habitat. This species' song ranges down to 0,784 kHz. It was found that the frequency spectrum of its song penetrates best within the species-specific habitat. The species also utilizes the theoretically optimal singing posts at the tops of the vegetation and is, therefore, very well adapted to its habitat.

Description / Table of Contents: Summary 1. In two groups of closely related species, the six Central European Acrocephalus (A. arundinaceus, A. palustris, A. scirpaceus, A. melanopogon, A. schoenobaenus, A. paludicola) and the three Locustella warblers (L. naevia, L. luscinioides, L. fluviatilis), the relationship between habitat, locomotion „on foot“ and foot morphology was investigated. 2. The sympatricAcrocephalus andLocustella species occupy rather different habitats. Their habitat requirements are related to particular vegetation structures which are mainly available in marshland and waterside situations. 3. Terrestrial locomotion in all nine species is described. All species hop and run, but the amounts of hopping and running show clear interspecific differences. Acrocephalus species mainly hop, and Locustella species mainly walk. These differences are related to the different habitats. As an exception, the Aquatic warbler mainly runs, whereas the Savi's warbler hops more than the other Locustella species. 4. The analysis of foot morphology is based on different measurements (foot span with and without claws, lengths of the four toes and the four claws). In addition, the shape of the foot sole and the size of its pads are described. Interspecific changes in the proportions of the different characters were shown by allometry. The functional significance of species-specific differences in foot construction were interpreted in terms of the characteristics found byRüggeberg (1960). The significance of the differences in foot construction is discussed in relation to adaptive radiation: Locomotion and foot construction are adapted to the specific habitat and favour niche utilization. On the other hand, specialization in locomotion as well as in foot construction lead to ecological isolation in different habitats: a) The perching foot of the Great reed warbler, Reed warbler and Moustached warbler is well adapted for clinging to vertical stems. The larger foot span of the Moustached warbler is adapted for clinging to broad blades and stalks. b) As an adaptation to the rank, herbaceous vegetation of its habitat, the Marsh warbler has a small foot. c) The rather generalized perching foot of the Sedge warbler is well adapted for locomotion in its particular habitat, with more heterogenous vegetation structures. The species mentioned so far depend on the availability of vertical rigid vegetation. d) In convergence to Locustella species the Aquatic warbler has evolved a walking gait, and a foot with short inner and outer front toes of almost equal length with a long central front toe. Alternate leg action and the ability to grasp several stalks by foot at once were important in filling an empty niche. e) Conversely, in invading a typical Acrocephalus habitat, the Savi's warbler has largely retained the walking foot typical of the genus Locustella. However, its long hind toe and large claws are indicative of the highest development of clinging ability within the genus. f) The proportions of the feet of the Grashopper and River warbler are ideal for walking. Because of their weak clinging ability for climbing vertical stems their possibility to choose song perches is limited. 5. Changes in both the construction and function of the foot have been achieved by altering the length of single elements of the foot. There are no examples of specialized locomotion without special adaptations in foot construction.

Description / Table of Contents: Summary This paper gives an overview of the ecomorphology of birds; particular points are illustrated with analyses primarily of our own data. The preferred method is to analyse morphological data from systematically close knit groups (genera, families). In all the examples presented, data, insofar as they were measurements rather than counts, were corrected for size by dividing them by the cube root of the lean body weight. With the exception of variables which could take on values of zero or less, they were then transformed to their logarithms. In Principal Component Analyses (PCA), correlation matrices were favoured over covariance matrices to weigh characters equally. Most examples refer to our own measurements of external and skeletal characters in Old World warblers, Sylviidae, chat-like thrushes, and tits. Fig. 1 shows the standard set of 32 measures used. The various problems of morphometrical analysis and functional interpretation are treated at different levels of organization, i.e. within species, between species, among genera, and in bird communities. Stepwise Discriminant Analysis was used to elucidate the differences between the willow tit and the marsh tit,Parus montanus andP. palustris, and to search for the most relevant characters (Tab. 1). Although the measurements were not adjusted for size, shape characteristics dominate the canonical axes. Willow tits have longer, more graduated tails and smaller feet than marsh tits. A plot (Fig. 2) of the canonical scores of separate analyses of hindlimb and forelimb characters shows the relationship between inter-species and intra-species variation. The Dartford warbler and Marmora's warbler,Sylvia undata andS. sarda, are differentiated by their flight apparatus and their hindlimbs, which reflects the preference of the Dartford warbler for low vegetation and for skulking in a cluttered habitat. The same analysis applied to four species ofPhylloscopus warblers reveals size and shape differences in the first canonical axis, which are mainly associated with long-distance movements, and morphological differences in the second, which correlate with increased use of arboreal habitats (Fig. 3). To analyse variation within genera,Sylvia with 11 species andParus with 6 species served as examples; PCAs of within species means of 32 characters were carried out. The first component of morphological variation of the warblers can be explained by differences in migratory behaviour and the vegetation of their breeding habitats, and the second by the diversity of locomotory habits which include the contrast between hopping and skulking and the ability to take off quickly or to break efficiently on the wing (Tab. 2, Fig. 4). In the first component of a PCA ofParus the contrast between square tails combined with large feet and long graduated tails with small feet dominates (Fig. 5). This component reflects differences in habitat structure while the second is mainly associated with the morphology of the bill and its diverse use. A PCA of sylviids demonstrates the importance of hindlimb characters for separating the various genera along the first component (Fig. 6). The second for the most part represents mainly differences in long distance migration. Cluster Analysis of the same data describes intergeneric and intrageneric similarities quite well, but is not amenable to straightforward ecological interpretation (Fig. 7). An analysis of the community of migrants in a southwest-German stopover-site illustrates several important points. Most of the morphological variation represented by the first and the second PC, which together explain 60% of the total variance, concerns characters related to locomotion. The first component expresses the contrast between aerial hunters on the low end and species which climb vertical stalks on the high end (Fig. 8). The systematic heterogeneity of the species set hampers more definitive interpretations. Morphological variation within genera does not affect all characters equally. The demands of migration determine variation in wing morphology of those genera containing migratory species. Genera comprised of residents and short distance migrants vary more only in bill measurements, whereas canopy dwellers (Parus, Phylloscopus) develop a variety of hindlimb features (Tab. 3). There are many interactions between single functional complexes of morphological characters. Important constraints arise for birds due to the problem of flight and weight. For example, there is a general tendency to appoint less mass to the hindlimb when flight musculature is well developed (Fig. 9). As other studies of fruit-eating birds demonstrate, interactions between grasping for fruits with the bill and the use of perches lead to correlations between bill and hindlimb characteristics. The incompatibility of some character combinations restrains the set of possible adaptations even within functional complexes. In warblers of the genusSylvia, for example, features suited for long distance migration are not congruent with certain modes of habitat use (Fig. 10). Yet characters within functional complexes may show diverse correlation structures in different systematic groups, so that the functional interpretation of the variation of single characters depends on the context of covariation with other characters (Fig. 11). This aggravates generalizations and poses a principal difficulty for the application of ecomorphological methods to problems of community ecology. Correlations between morphology and ecology can only be understood if the relevant behaviour is known. Bill shape can be modified according to specific feeding techniques. Seasonal variation in behaviour can match changes in morphology. Sexual differences and social status are other variables which may influence ecomorphological relationships. Valuable insights can be gained when morphological, ecological and ethological data about several species are available. Regression Analysis and Canonical Correlations can be used to describe the relationships and to select the appropriate characters for interpretation and further studies (Fig. 12). Examples for relations between feeding techniques and morphology are presented in Figs. 13, 14 and 15. Besides such studies of correlations, experimental corroboration of the causal interplay of behaviour, morphology, and ecology is needed. Some examples for such studies are reviewed. In conclusion, it must be stressed that many ecomorphological studies, particularly those concerned with community ecology, fail to recognize the importance of selecting a representative set of characters which also have some functional meaning. The results of studies of the type advocated here may stimulate ecologists as well as morphologists. More ecomorphological work needs to be devoted to the role of morphology in constraining behaviour, to the problem of morphological changes caused by differential use, to the generalist-specialist continuum, and to convergent evolution.

Description / Table of Contents: Zusammenfassung In zwei aufeinanderfolgenden Brutzeiten wurde die Raumnutzung von Seggenrohrsängern mittels Telemetrie untersucht. Die ermittelte Größe der Streifgebiete von Männchen betrug in der gesamten Brutzeit bis zu 8 ha. In dem Streifgebiet eines einzelnen Männchens wurden bis zu elf telemetrierte Männchen festgestellt. Die Überlappungen der Streifgebiete telemetrierter Männchen betrugen durchschnittlich 51 %, maximal 74 %. Weibchen nutzten während der Paarungszeit nicht zusammenhängende inselartige Areale von insgesamt 2,8 bis 6,4 ha (Mittelwert 4,2 ha) innerhalb von Aktionsräumen von 110 bis 160 ha (Mittelwert 120 ha). Diese Areale überlappten zu 20 % mit den Aufenthaltsgebieten anderer Weibchen. Während des Brütens sank die Größe der Streifgebiete der Weibchen auf durchschnittlich 1,6 ha. Da im Beobachtungszeitraum keine konstant genutzten Aufenthaltsgebiete vorlagen, schließen wir, daß sich Seggenrohrsänger in der Brutzeit nicht territorial verhalten.

Description / Table of Contents: Summary 1. The Marsh Warbler(A. palustris) may be distinguished from the Reed Warbler(A. scirpaceus) in that the former has a smaller foot, with shorter toes than the latter. 2. Various measurements of elements of the feet were taken from adults, which were identified with certainty. These were tested for their selectivity. In all the segments investigated, it was found that the foot of the Marsh Warbler was proportionately shorter. The measurements of single segments showed little difference between the two forms, however if summed up, the compound measurements showed significant differences. 3. The best criterion was found to be the measurement of the inner foot span (taken from the tip of the hind claw to the tip of the inner claw). The mean measurement of this for the Marsh Warbler was 25,0 mm, and for the Reed Warbler 27,8 mm. 4. The functional significance of these differences in foot morphology were discussed. The Marsh Warbler is not as well adapted for climbing vertical stems as the Reed Warbler. Correspondingly, the foot elements, important for climbing vertically, were weaker.