Volume 25 - N. 2
December 2001

Avocetta
Volume 25 - N. 2



  1. The Golden Eagle Aquila chrysaetos in Crete. Distribution, population status and conservation problems

    Xirouchakis S.

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    20 73

    The post 1990 distribution and status of the Golden Eagle Aquila chrysaetos was investigated in a four-year study on the island of Crete. Total foraging and breeding range is about 5,200 km2 (63% of the island’s surface) although eagles are regularly sighted over an area of 3,200 km2. Population comprises of 16 breeding pairs or an estimated 60 birds. The mountains of Lefka Oroi, Idi (Psiloritis) and Dikti support the greatest eagle concentration with a mean population density of 0.63 breeding pairs per 100 km2. Mean annual productivity was estimated at 0.51 eaglets per territorial pair with a rate of one successful breeding attempt every 2.6 years. The average home range size was 79 km2 ranging from 45 km2 to 110 km2. Site occupancy is irregular in a number of territories due to human persecution which is also suspected to be the reason for territories occupied by single adult birds or mixed pairs of adult and pre-adult individuals (mean= 21%, range = 17-28%). Land use changes threaten the species’ long-term survival since the abandonment of terraced agriculture, overgrazing in combination with fire and road construction have caused the degradation of its habitat. Protection of mountain areas, control of poaching, decrease in stocking density and the implementation of hunting controls are the most desirable conservation actions.

  2. Purple Heron diet in northern Spain. Differences between feeding areas and between sampling methods

    Campos F., Lekuona J. M., Rios M., Miranda R.

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    26 58

    Purple Heron (Ardea purpurea) diet was analysed by observing foraging adults in rivers and ricefields in northern Spain and by taking food samples from nests (pellets, food remains and spontaneous regurgitates). Diet composition varied between feeding areas (fish were the most abundant prey in rivers and crayfish Procambarus clarkii in ricefields) and sampling methods (direct observations underestimated the importance of insects and overestimated crustaceans and amphibians). The Purple Herons in the study area seemed to have adapted their diet to a new trophic resource (the crayfish) recently introduced in the study area.

  3. Peninsular patterns of breeding landbird richness in Italy: On the role of climatic, orographic and vegetational factors

    Battisti C., Testi A.

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    17 59

    In this study, an analysis of the breeding landbird distribution patterns in the Italian peninsula in relation to climatic, orographic, and indirectly, to vegetational factors has been carried out. Data were drawn from the Atlas of Breeding Birds in Italy (Meschini and Frugis, 1993) and arranged in latitudinal bands (LB). Three matrices (species/latitude, species/classes of LB with same bioclimatic Mediterranean area, species/ classes of LB with same altitudinal ranges) were obtained and analyzed with multivariate statistics. Comparations with thematic maps at national scale highlight that differences in the species richness among LB are localized in corrispondence with orographic, bioclimatic, geobotanic, anthropic discontinuities along the peninsula. Results, interpreting the preceding hypotheses on latitudinal changes of species richness, have evidenced that fauna changes occur at bioclimatic and orographic thresholds. These changes are due, in part, to quantitative differences in the number of species among the latitudinal bands, and in part to qualitative differences which will be investigated in successive works. Floristic and physiognomic-structural changes of vegetation probably contribute, indirectly, to these. Climate at macroscale level, orography and vegetation at mesoscale level, may influence the observed patterns. Thus, a primary role of physical factors and a secondary role of biological ones, is confirmed in determining the breeding landbird richness patterns in peninsular Italy.

  4. Laying dates, clutch size and breeding success in the Pallid Swift Apus pallidus in Sofia, Bulgaria

    Antonov A., Atanasova D.

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    20 66

    Breeding biology of Pallid Swift Apus pallidus was studied between 1997 and 2000 in Sofia city, a place lying at the northern boundary of the species’ range on the Balkan Peninsula. It was found that first clutches were laid mainly during the second half of May and second clutches – the end of July and the first half of August. Breeding period in Sofia tended to be more compressed and synchronized compared to that in Piedmont (NW Italy). The proportion of pairs laying second clutches was 55 %, 90 % and 66 % in 1998, 1999 and 2000 respectively. Pallid Swifts laid on average 2.93 ± 0.54 eggs (2 -4) in the first clutches and 2.12 ± 0.48 eggs (1-3) in the second clutches. Comparisons with other colonies of this species in Piedmont (Italy), Gibraltar, Tunisia and Corse showed that clutch size of both first and second clutches was highest in Sofia. First breeding had an average overall success of 2.6 fledged young/pair and second breeding – 1.4 fledged young/pair. Values of the fledging rate proved greatest in Sofia though significantly different only in relation to Gibraltar.

  5. Column - Nuovi avvistamenti

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    26 171
  6. Observation of a breeding trio in the Cory’s Shearwater Calonectris diomedea on Selvagem Grande

    Mougin J.L. , Jouanin Chr., Roux F.

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    23 43

    Chez le Puffin cendré Calonectris diomedea de Selvagem Grande (30°09’N, 15°52’W), un trio a été observé. Sur le même nid, deux mâles et une femelle ont couvé en alternance un œuf qui a éclos et produit un poussin heureusement envolé trois mois plus tard. Un tel comportement est probablement la conséquence exceptionnelle des visites exploratoires effectuées dans les colonies pendant la pariade par les jeunes oiseaux à la recherche d’un partenaire et d’un nid.

  7. Resti vegetali nelle borre di civetta Athene noctua (Scopoli, 1769)

    Fontaneto D., Guidali F.

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    20 55

    We report data on the presence of vegetable matter in pellets of the Little Owl, Athene noctua (Scopoli, 1769). The presence of vegetable remains seems to be positively related to remains of invertebrates with hard cuticle, and negatively related to remains of fur of little mammals and feathers of birds. The Little Owl could so ingest vegetable matter to help pellet egestion.

  8. Column - Book Reviews

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    21 60