Volume 22 - N. 1/2
1/2 1998

Avocetta
Volume 22 - N. 1/2



  1. Rotte di homing e attività di foraggiamento degli uccelli studiate mediante l’uso di un data-logger: risultati conseguiti e prospettive per il futuro

    Benvenuti S., Dall’Antonia L. & Ribolini A.

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    13 89

    A new type of bird-borne data logger can record directional data which allow the reconstruction of the whole path flown during the homing process. This direction recorder, devised and manufactured by our research group and originally designed to study the pigeons’ homing behaviour, has recently been used in studies of wild birds. Our instrument has succesfully been used in investigations of the homing strategies of Cory’s shearwaters (Calonectris diomedea) transported and released at sites far from their breeding colony. The direction recorder has also been used in a study of the foraging activity of Brünnich’s guillemots (Uria lomvia) breeding at Latrabjarg (NW Iceland); the recorded data have allowed us to reveal aspects of the birds’ feeding strategies which were poorly known due to a lack of adequate technology. The recent versions of the data logger, equipped with new devices which can record the flight activity and the diving profile, have open new interesting perspectives for the study of birds’ ecology and behaviour.

  2. The passerine fauna of the wetlands on the North coast of the Black Sea, with emphasis on the Paddyfield Warbler (Acrocephalus agricola)

    Schogolev I.

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    18 37

    Seven species of passerine (Order Passeriformes, Class Aves) were studied at several wetlands on the North coast of the Black Sea from 1983 to 1997. Each species appeared to be considerably specialized in the kind of habitat it occupied, and as a result there were significant differences in the fauna of the wetlands according to the type of habitat present. Freshwater deltas are richest in species, despite varying water levels, while coastal sea water sand bars were occupied by only one species, the Paddyfield Warbler Acrocephalus agricola septima.

  3. Bird community in a Beech forest in Lower Savinja Valley (Slovenia)

    Vogrin M.

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    15 46

    Bird census work was carried out in the forest (30.8 ha) at the edge of the Dobrovlje karst plateau in Lower Savinja VaIley (Slovenia), belonging to the Luzulo-Fagetum phytocenosis and Blechmo-Fagetum forest. The main species of the forest are: Fagus sylvatica, Quercus petraea, Pinus sylvestris and Picea abies. Twenty-six bird species were reported in the forest and the average density was 30.2 pairs/10 ha. The abundance (biomass) of the bird community is 2078 g/10 ha. The highest densities of breeding pairs were noted for Parus ater and Erithacus rubecula. The Index of Diversity (H’) was 2.82 and the Evenness Index (Je) was 0.87. Breeding communities were also analyzed in relation to the nesting site, feeding and migratory habits. Among the breeding species, five were trans-Saharian migrants and five were only short-distance migrants. Nine species (33.6 %) are insectivorous (carnivorous) species, four (15.4 %) are herbivorous and thirteen (50 %) are omnivorous. The density of the breeding avifauna in the beech forest depended primarily on the density of species nesting in the crowns of trees and from hole-nesters (both 11.4 pairs/10 ha), on the density of omnivorous species (19.1 pairs/10 ha) and residents (16.2 pairs/10 ha). The breeding population of the Zovnek beech forest has a species composition markedly different from other forests compared here(Sorensen’s lndex of Similarity varied from 27 to 75, and the Renkonen lndex varied from 14.3 to 61.2).

  4. Sopravvivenza e filopatria della Rondine (Hirundo rustica) in Italia settentrionale

    Ferro G. & Boano G.

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    10 62

    From 1988 to 1996 13024 Swallows were ringed in a rural area of about 65 Km2 square near Bra (Italy, NW). The analysis of recaptures shows a high breeding-site philopatry: 93% of adults recaptured in the study area (15% of the adults ringed) returned to the previous breeding site. Natal philopatry was low and only 1% of the birds ringed as nestling were recaptured in successive years in the study area, and 80% of these chose a different site from that of their birth. In view of the high breeding-site philopatry we would expect that the permanent emigration of breeding birds from the area to be very low, so that the capture-mark-recapture survival estimate for the adults (36%, s.e 2%), obtained using Jolly-Seber models, will have provided a good estimate of adult survival. In contrast, the survival estimate for juveniles (3%) is certainly strongly negatively biased due to the low natal philopatry (i.e. high emigration rate). Capture-mark-recapture data of sexed adults also permitted the differential survival rates of males (37%, s.e. 3%) and females (26%, s.e. 2%) estimates. The adult survival estimate is comparable to other estimates obtained with ringing recoveries and is therefore probably unaffected by the emigration rate, but the lower females survival rate, if not due to a higher emigration rate than males, could explain the observed population decline in spite of a normal breeding success.

  5. Diet of the Black-eared Wheatear Oenanthe hispanica in relation to food availability in two arid shrubsteppes

    Hòdar J. A.

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    18 50

    The diet of Black-eared Wheatear Oenanthe hispanica was studied by faecal analysis in two arid shrubsteppe zones of southeast Spain. A total of 197 faeces collected in spring and summer contained recognizable remains of 826 prey. Formicidae, Coleoptera and Orthoptera were the main prey taxa in the diet, both in number of prey items as well as in the amount of biomass provided. Diet composition showed marked variations throughout the study period; differences between zones were also found. Prey size was smallest in mid-summer, when the main prey type was predominantly worker ants, and largest in spring and late summer. Prey availability, measured using pitfall traps, was related to diet. Only Orthoptera and Heteroptera were positively selected over the entire study period. Ants, due to their great abundance, appeared to be consumed below availability, despite their high frequency of consumption. The vegetal fraction in the diet was small, consisting mainly of Caper (Capparis spinosa) fruit. The Black-eared Wheatear appears to behave as a generalist feeder, with a diet based on the abundant ants and supplemented with other more profitable groups when found.

  6. Ruolo dei sessi nella riproduzione della Sterpazzola di Sardegna, Sylvia conspicillata, nell’Italia centrale

    Guerrieri G., Santucci B. & Castaldi A.

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    14 40

    The reproductive role of sexes in Spectacled Warbler has been studied during four years in a sample site of Central Italy (n = 28 pairs and 4 territorial unmated males). Male’s song activity reaches the top during nest building. The male is particularly involved in nest construction and protection, while female helps male by adding nest-line materials. Intraspecific territoriality among males persists for a short time and aggressive interactions are modest. The pair incubate the eggs with an evident differences between sexes. About 75 % of males take part in eggs covering with a less frequent care in respect to females (- 50 %). A few males (3.6 %) don’t incubate and 21.5 % incubate irregularly. Periods spent by both parents sitting on eggs vary during the day and eggs are covered during 61.7 % of the day times. Chick feeding increases along the breeding season and female seems to be more active in the morning. The members of the couple are very autonomous and the pair is able to begin a second reproduction even also the first is not completed yet.

  7. Breeding distribution of the Dipper Cinclus cinclus in the Reno valley (Appennino Emiliano, Northern Italy)

    Andreotti A., Riga F. & Rossi G.L.

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    14 52

    This work was carried out with the aim of collecting information with regard to the breeding of Dippers (Cinclus cinclus) in the upper part of the Reno valley (Appennino Emiliano, Northern Italy) and to correlate the nesting pair distribution with ecological parameters of the watercourses, with particular reference to water quality, assessed by I.B.E. method. The results have shown that the species is widely spread along the surveyed streams, most likely because of climatic conditions, producing a positive effect on the flow of the rivers, and the generally good condition of the stream banks and beds. Water quality measures performed through I.B.E. procedures on seven sampling stations have not revealed correlations between the presence of the Dipper and the evaluated variables. Accordingly, it is considered that limiting factors for this species could be related to criteria not taken into account in this research.

  8. Foraging behaviour and habitat use in corvids wintering on farmlands in northern Italy

    Rolando A., Peila P. & Marchisio M.

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    18 79

    Foraging behaviour and habitat use of corvids (Hooded and Carrion Crows, Rooks, Magpies) wintering on farmlands have been studied in the western Padana Plain (northern Italy). All species foraged prevalently on meadows and maize stubbles. Differences in the proportions of use of crops were not significant between Hooded and Carrion Crow, whereas they were significant in every other comparison between species. Foraging techniques were opportunistically used according to the foraging habitat choosed. Surface pecking was the commonest technique for every species, while digging was often displayed by the Rook only. Feeding rates varied according to the crop types used. Rooks fed significantly quicker than others on dunged meadows and harrowed fields, whereas Magpies fed slower than others on maize stubbles. The highest feeding activity of the Rook was obtained by means of an unremitting pecking activity and a wide use of all the different foraging techniques. No significant difference in feeding rates was found between Hooded and Carrion Crows. Both habitat use and foraging behaviour changed from area to area, suggesting that foraging ecology of corvids largely depends upon local environmental conditions. Flocks of Hooded Crows and Rooks were significantly more numerous when Carrion Crows and Hooded Crows were present, respectively. However, these data may be interpreted without assuming that interspecific competiton affects flock size.

  9. Behavioural development in young Bearded Vultures Gypaetus barbatus reintroduced in the Alps

    Rolando A., Toffoli R., Fornerone I. & Carisio L.

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    10 49

    The behavioural development in young Bearded Vultures released at the Argentera-Mercantour site prior to and immediately after departure from the artificial nest was analysed to provide a detailed description of the development of the main behavioural activities and to check for the occurrence of anomalies. Six individuals released from 1994 to 1996 were continuously monitored using telescopes. Regression analyses pointed out that three vultures during the period at the nest progressively increased the time spent on watching and feeding and hence decreased that spent resting. Then, after leaving the nest, most vultures progressively increased the time spent on feeding and flying and decreased that spent resting and walking. Percentages of significant regressions were lower in the first period (54%) than in the second (72%). This, together with the output of the analysis of covariance, suggests that the period at the nest may be more critical than that after leaving it. However, wing fluttering at the nest progressively and significantly increased in four out of six vultures. Once they have left the nest, most birds showed increased vigilance, selected roosting sites which were protected from terrestrial predators, and successfully interacted with crows at feeding sites. Finally, a few observations suggested that birds were able to drop bones autonomously. Our results, which are in keeping with previous observations, suggest that young vultures are able to overcome the difficulties they meet after release, probably because many behaviours are largely genetically controlled. Hence, we may assume that the final outcome of the reintroduction project of the Bearded Vulture in the Alps will not be significantly affected by the hacking technique employed.

  10. Migration patterns of the Common Sandpiper Actitis hypoleucos and its habitat choice during migration in northeastern Slovenia

    Vogrin M.

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    13 50

    During the years 1985-1996 migration patterns of Common Sandpiper Actitis hypoleucos and its habitat choice were studied on Dravsko polje in northeastern Slovenia. The peak period in spring is in the second half of April, whereas the peak period in autumn is less pronounced. The majority of Common Sandpiper seen during the migration were recorded in drained fishponds. During the autumn migration single bird occur more frequently then flocks, whereas differences during spring period was not significant.

  11. Book reviews

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    14 45