Reto Spaar

Ecological and social effects on reproduction and local recruitment in the red-backed shrike

Numerous hypotheses have been proposed to explain variation in reproductive performance and local recruitment of animals. While most studies have examined the influence of one or a few social and ecological factors on fitness traits, comprehensive analyses jointly testing the relative importance of each of many factors are rare. We investigated how a multitude of environmental and social conditions simultaneously affected reproductive performance and local recruitment of the red-backed shrike Lanius collurio (L.). Specifically, we tested hypotheses relating to timing of breeding, parental quality, nest predation, nest site selection, territory quality, intraspecific density and weather. Using model selection procedures, predictions of each hypothesis were first analysed separately, before a full model was constructed including variables selected in the single-hypothesis tests. From 1988 to 1992, 50% of 332 first clutches produced at least one fledgling, while 38.7% of 111 replacement clutches were successful. Timing of breeding, nest site selection, predation pressure, territory quality and intraspecific density influenced nest success in the single-hypothesis tests. The full model revealed that nest success was negatively associated with laying date, intraspecific density, and year, while nest success increased with nest concealment. Number of fledglings per successful nest was only influenced by nest concealment: better-camouflaged nests produced more fledglings. Probability of local recruitment was related to timing of breeding, parental quality and territory quality in the single-hypothesis tests. The full models confirmed the important role of territory quality for recruitment probability. Our results suggest that reproductive performance, and particularly nest success, of the red-backed shrike is primarily affected by timing of breeding, nest site selection, and intraspecific density. This study highlights the importance of considering many factors at the same time, when trying to evaluate their relative contributions to fitness and life history evolution.

TO CROSS THE SEA OR TO FOLLOW THE COAST? FLIGHT DIRECTIONS AND BEHAVIOUR OF MIGRATING RAPTORS APPROACHING THE MEDITERRANEAN SEA IN AUTUMN

Summary We studied the flight behaviour of migrating raptors confronted with the Mediterranean sea at an average coast site near Malaga (Spain) in autumn by means of a tracking radar. Behavioural reactions to the water barrier were species-specific, but modified by environmental conditions. Honey buzzards Pernis apivorus and black kites Milvus migrans were reluctant to crossing the water and followed the east-west leading coast; the few honey buzzards crossing the sea at the end of the migratory period were probably juveniles. Considerable numbers of harriers Circus sp., falcons Falco sp. and ospreys Pandion haliaetus crossed the Mediterranean sea. Falcons crossing the sea had higher flight altitudes than those following the coast or crossing the bay. Sea crossings occurred preferably in following winds and also in sidewinds, whereas no birds were observed to cross the sea in strong opposing winds. However, tailwind-support only partly explained for different migratory routes. Raptors crossing the sea in flapping-gliding flight increased airspeeds with sidewinds to reduce drift, but, different from theory, they did not decrease airspeed with increasing tailwind-support indicating that they minimised flight time above sea. Time and energy related consequences of different flight routes are discussed.

Migration by Flapping or Soaring: Flight Strategies of Marsh, Montagu's and Pallid Harriers in Southern Israel

Migratory flights of Marsh Harriers (Circus aeruginosus), Montagus Harriers (Circus pygargus) and Pallid Harriers (Circus macrourus) in southern Israel were used to test flight theory predictions. The body sizes of these closely related species are between those of the typical large soaring migrants, such as eagles and storks, and the typical flapping migrants, such as small falcons and sparrowhawks. In soaring-gliding flight, Marsh Harriers reacted to different thermal conditions by adjusting their gliding airspeed to the actual climbing rate in thermal circling; consequently, cross-country speed was related to climbing rate. In contrast, the smaller Montagus and Pallid Harriers did not adopt gliding airspeeds according to thermal conditions. All harrier species regularly used flapping-gliding flight, predominately soon after sunrise and before sunset, and more often in opposing winds than in following winds. Montagus/Pallid Harriers used flapping-gliding more frequently than Marsh Harriers. Because they alternate between different flight styles, harriers are more independent of environmental factors, such as thermal activity and wind, compared to pure soaring migrants. This allows harriers to migrate under unfavorable thermal and wind conditions. Marsh Harriers are similar to typical soaring migrants in maximizing cross-country speed in soaring-gliding flight, whereas Montagus and Pallid Harriers are less adapted to soaring-gliding flight and thus are similar to smaller flapping migrants. Optimal soaring-gliding flight seems to be less relevant for these smaller harriers; they maximize cross-country performance by efficiently combining different flight styles.

Migratory flight strategies of Levant sparrowhawks: time or energy minimization? ☆

Diurnal and nocturnal flight paths of 364 Levant sparrowhawks, Accipiter brevipes, were recorded by radar and used to analyse migratory strategies. Soaring-gliding was the predominant flight strategy during the day when thermals were available. Also during the day, and at night, flapping-gliding flight was used. Levant sparrowhawks flew at similar altitudes as other migrating raptors in Israel during the day; however, they showed different diurnal patterns, using flapping flight at high altitudes soon after sunrise and late in the afternoon. Migratory directions were strongly concentrated on a south-southwest-north-northeast axis in spring and autumn, whereby birds compensated for lateral drift. Soaring-gliding birds maximized cross-country airspeed according to optimal flight theory and, thus, minimized time needed per distance. In flapping-gliding flight, they adjusted their airspeed with respect to the wind to fly at the maximum range speed, suggesting that they minimized energy consumption per distance. Calculations based on aerodynamic flight theory showed that the optimal migratory strategy of a Levant sparrowhawk with respect to time and energy depends on feeding conditions en route: in poor conditions, both time and energy are minimized by a pure soaring-gliding flight strategy. If food is available en route, soaring-gliding flight should be combined with flapping flight when no thermals are available, as this will minimize time spent on migration. The evidence for both strategies is discussed. Copyright 1998 The Association for the Study of Animal Behaviour.

FLIGHT BEHAVIOR OF STEPPE BUZZARDS (BUTEO BUTEO VULPINUS) DURING SPRING MIGRATION IN SOUTHERN ISRAEL: A TRACKING-RADAR STUDY

ABSTRACT In spring 1992, steppe buzzard migration was studied by tracking radar in the Arava Valley near Hazeva (150 m below sea level) and in the Negev Highlands near Sede Boqer (470 m above sea level). Entire gliding and soaring phases were recorded. The flight altitude of the steppe buzzards depended on the time of day. Migration was slightly higher above ground and lasted longer towards sunset in the Arava than in the Negev. The maximum altitudes, about 2000 m above ground in the Arava and about 1000 m in the Negev, were reached in the early afternoon. The relatively low average climbing rates in thermals of 2 m/s can be explained by the fact that the whole diurnal circle is included in this average and that the observation sites were not situated at the edge of large rocky slopes where large thermal updrafts occur, but rather on flat surfaces. Strong thermals were used longer for soaring than weak ones. The climbing rate in thermals was a decisive trait when explaining the flight behavior of migratin...

The 50 most important questions relating to the maintenance and restoration of an ecological continuum in the European Alps.

The European Alps harbour a unique and species-rich biodiversity, which is increasingly impacted by habitat fragmentation through land-use changes, urbanization and expanding transport infrastructure. In this study, we identified the 50 most important questions relating to the maintenance and restoration of an ecological continuum – the connectedness of ecological processes across many scales including trophic relationship and disturbance processes and hydro-ecological flows in the European Alps. We initiated and implemented a trans-national priority setting exercise, inviting 48 institutions including researchers, conservation practitioners, NGOs, policymakers and administrators from the Alpine region. The exercise was composed of an initial call for pertinent questions, a first online evaluation of the received questions and a final discussion and selection process during a joint workshop. The participating institutions generated 484 initial questions, which were condensed to the 50 most important questions by 16 workshop participants. We suggest new approaches in tackling the issue of an ecological continuum in the Alps by analysing and classifying the characteristics of the resulting questions in a non-prioritized form as well as in a visual conceptualisation of the inter-dependencies among these questions. This priority setting exercise will support research and funding institutions in channelling their capacities and resources towards questions that need to be urgently addressed in order to facilitate significant progress in biodiversity conservation in the European Alps.

Saisonaler Verlauf der Gesangsaktivität der Singdrossel (Turdus philomelos), mit Anmerkungen zum nachbrutzeitlichen Gesangsschub

This study was carried out at the Zürichbergwald, a forest east of Zurich (47°20′N/08°30′E). The study site is a wooded hill of 350 ha between 480 to 680 m asl, characterised by a BeechFagus silvatica forest with patches of SprucePicea abies on 25 % of its surface. The Zürichbergwald is a popular recreational area with moderate forestry exploitation. We did not differentiate acoustic registration from singing activity, and we considered the number of singing males per km to be a measure for singing activity. Two different approaches were applied: in 6 breeding seasons (1989 and 1991 to 1995) JH counted birds at sunset on a 6.1 or 7.1 km circuit (n=123). In 1990, the same was done by RS at dawn each morning on a zigzag track of 6.7 km (n=46). Also in 1990, RS sampled data on the breeding biology of the species. The annual cycle of morning and evening song activity was significantly correlated (Spearmans rank-test; p<0.001 comparing pentads, p=0.025 comparing half of months). Morning and evening revealed the same pattern: there was a first large peak of singing activity early in the year (earliest onset of singing 19 February 1989; latest 8 March 1993) until 5 April (phase I). A period of low song activity followed from 6 April to 15 May (phase II). The period from 16 May to (circa) 5 July was characterized by a second large peak (phase III). Each of the corresponding phases was comparable between morning and evening (Wilcoxon matching pairs; p>0.05). The analysis of evening data reveals that phase II differed from I and from III (p=0.05), but the last two did not differ significantly (Wilcoxon matching pairs; p>0.05). The day with the highest song activity fell in phase I twice (maximum 6.1 singing males/km, 2 April 1995) and 5 times in phase III (maximum 6.9 singing males/km, 23 May 1994). The date females first laid was determined for 53 out of 68 nests. The first brood started 25 March, the last 25 June 1990. Only 3 broods were initiated later than 5 June. The first peak of singing activity could be correlated with the (delayed) onset of breeding, but the second started at the end of the breeding season and persisted too long to be correlated with any breeding activity such as female attraction or stimulation, mate-guarding, etc. We postulate the high post-breeding song output to have several possible functions: Song instruction by father to offspring, or territory announcement for the next season. Der Zürichbergwald ist eine 350 ha große, bewaldete Kuppe auf 480–680 m ü.M. am Rande der Stadt Zürich. Hier untersuchten wir von 1989 bis 1995 die jahreszeitliche Gesangsaktivität der Singdrossel mit zwei verschiedenen Ansätzen. 1989 und 1991–1995 zählte JH an 123 Tagen auf zwei festgelegten Strecken von 6,1 und 7,1 km die Sänger jeweils in der Stunde der abendlichen Dämmerung. Im gleichen Gebiet zählte RS 1990 an 46 Tagen auf einer 6,7 km langen Strecke am Morgen in der Stunde nach Sonnenaufgang. Ebenfalls 1990 sammelte RS Daten zur Brutbiologie. Die Gesangsaktivität definierten wir mit der Anzahl singender Männchen pro km. Im Jahresverlauf zeigen die Kurven der Morgen- und der Abendaktivität keinen Unterschied. Die Kurve ist deutlich dreiphasig: Ein erster Gesangsschub vom Eintreffen der Vögel bis zum 5. April, danach eine gesangsarme Zwischenzeit bis zum 15. Mai, gefolgt von einem zweiten Gesangsschub, welcher bis zum 5. Juli dauern kann. Allenfalls ist der erste Gesangsschub (stark zeitverschoben) mit dem Beginn der Erstbruten korreliert; die von vielen Singvögel bekannte, markante Gesangsaktivität unmittelbar vor der Eiablage gibt es nicht. Der zweite Gesangsschub ist in der Stärke mit dem ersten vergleichbar. Allerdings liegt er eindeutig am Ende der Brutzeit und kann nicht mit einem Brutparameter (Partnerfindung, Paarbindung, Balz, Brut-Stimulation) in Zusammenhang stehen. Die Funktion dieser nachbrutzeitlichen Gesangsaktivität scheint zukunftsbezogen zu sein. In Frage kommt gehäuftes Singen der Väter vor den Jungen zum Erlernen des Gesangs und des Dialekts, oder/und eine Revier-Voranzeige für die nänchste Brutsaison durch die als philopatrisch bekannten Männchen.