Volume 17 - N. 1
June 1993

Volume 17 - N. 1

  1. Avocetta n.17 (1) - 1993

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    20 448
  2. Nest-hole selection as defence measure in breeding Swifts (Apus apus)


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    27 91

    During the 1990-1991 breeding seasons we studied factors affecting Swift nest-hole selection,
    i.e. exposure, height, dimensions, type of holes and dispersion, in Pavia, Northern Italy. Exposure
    was not a significant factor, while in most cases Swifts nested at a height of 9-14 m in very small
    holes, often barely large enough to let them in. Holes were the sites selected in most cases; however
    a number of Swifts used the spaces under tiles, and a small number nested under eaves or behind shutters.
    Swifts were found nesting at 1-2 m maximum distance, confirming that nest-aggregation is another
    important factor in hole selection.

  3. Umbrella pine seeds selection by Hooded Crow,  Corvus corone cornix


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    18 44

    Probably the Hooded Crow selects longer and heavier pine-seeds to obtain bigger endosperms
    or to select the full pine-seeds. The old valve absence among the pine-seeds opened by the Hooded
    Crow also confirms the latter hypothesis.Smaller pine-seeds having a more elongated shape are opened
    on anvils, maybe because they are more difficult to break open, but the different techniques used to
    open pine-seeds on the ground and anvils stili need further study.

  4. Breeding habitats of Sparrowhawks (Accipiter nisus) and Goshawks (A. gentilis) in the Southern Alps


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    23 46

    The breeding habitats of Goshawks and Sparrowhawks were studied at the level of the
    nest site, of the area close to the nest, and of the presumed home range. The generai features of the
    home ranges of the two hawks coincided. In contrast, both the territories and the nest sites differed
    sharply: compared to the Sparrowawk, the Goshawk preferred territories where trees were older, bigger,
    and spaced at wider distances, and where the shrub and tree cover was lower, and the grass cover
    was higher. These preferences may be related to the size difference, and to interference competition
    between the two hawks.

  5. Breeding population and distribution of the Oystercatcher (Haematopus ostralegus) in Italy


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    19 59

    The whole Italian population of Oystercatcher (Haematopus ostralegus) breeds along the
    north-east coastline; 36 pairs were censused in 1991 and 42 in 1992. They are mostly restricted to the
    barrier islands of Po Delta and to the lagoon of Grado-Marano. In the favourable breeding areas,
    a mean density of 1.92 (1991) and 1.84 (1992) pairs per km was recorded, with a minimum distance
    between nests of 45 m. Nest site fidelity in the years 1991-1992 was 58.3%. Over the last ten years
    the ltalian breeding population, one of the most important of the Mediterranean area, has shown
    irregular fluctuations.

  6. Notes on the lek behaviour of the Little Bustard in Italy


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    21 61

    The display behaviour of Little Bustard (Tetrax tetrax) males was studied in Sardinia and
    in Apulia.
    Little Bustard males occured from Aprii to June in steppe-like habitats and cJustered in display centers
    with average density of 1.9 males/lOO ha. Mean nearest neighbour distance was 450 m.
    The habitat of the area exploited by the birds consisted mainly of permanent pastures grazed by sheep
    and cattle, secondly of oat/barley fields and fallow land.
    The birds were mostly active at dawn and dusk, giving snort calls at the maximum frequency of 1
    call/9.3 seconds. More elaborate courtship display, Iike wing flashing and jumping, occurred only
    in twilight.
    The author compares the behaviour of Sardinian and Apulian males, finding out some differences
    in the pattern of display.
    In Sardinia males showed complete courtship display and occurred always in relaxed groups, while
    in Apulia the males were never record ed wing flashing or jumping and sometimes they were so dispersed
    as to be considered “soloists”.

  7. Stress antropogenici ed evoluzione di una comunità ornitica in una zona umida artificiale dell'Italia centrale


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    20 47

    Si è studiata l’evoluzione di una comunità ornitica in un area umida dell’Italia centrale
    sottoposta a stress antropico. L’analisi condotta in una piccola area (25 ha) dal dicembre 1986 al gennaio
    1992. Il disturbo antropico è stato correlato alla diminuzione degli uccelli; si rileva un’azione combinata
    di diversi fattori quali inquinanti chimici, diminuzione della vegetazione sommersa, taglio e bruciatura
    del canneto. La pesca e l’attività di ricreazione non solo minacciano la presenza di uccelli acquatici
    a causa della diminuzione dell’habitat utilizzabile ma riducono anche la capacità portante dell’ambiente.
    La presenza del Germano Reale e del Moriglione sono correlati con la diminuzione di Myriophillum;
    La diminuzione della Folaga sembra dovuta all’aumento di vegetazione sia sommersa che emersa.
    L’Airone Cenerino patisce particolarmente il disturbo antropico. Il trend negativo descritto per questa
    zona non è altrettanto evidente in altri ambienti umidi costieri della Regione.

  8. Variability of the entomatic diet of the Hooded Crow Corvus corone cornix  in the western Po Valley


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    22 50

    A study was performed on the entomatic food supply of the Hooded Crow Corvus corone
    cornix in two different areas of the Po Valley. Significant differences were observed in geographical,
    seasonal and monthly terms. The analysis of the stomach contents in terms of the abundance of a
    given taxon/stomach did not correspond in generai with the classical analysis of the frequencies with
    which the various taxa were found. The data obtained confirm the broad-based behaviour of the species
    and reveal that the Crow takes advantage of the local availability on an and hoe basis.
    Within the framework of this behavioural model, however, the species is able to select certain crop
    types if they are actractive (the rice-fields in spring-surnrner), and appears to be ready to takes advantage
    of the concentration of prey in given sites (Formicidae in nests, Diptera pupae in dung) and their seasonal
    behaviour (Staphylinidae wintering under stones).

  9. Bird-borne satellite transmitters: current limitationsand future prospects

    Benvenuti S.

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    20 57

    The paper provides a brief account on satellite tracking, a new promising method for
    studying bird migration and orientation. This method is based on two Tyros-N satellites which receive
    and locate the signals emitted by bird-borne transmitters. The literature on this topic is stili very limited,
    due to the fact that this technique, which is only a few years old, has not yet left the pionieristic phase.
    However, technical problems concerning the weight of transmitters – and their short operative lifetime
    – which presently pose severe limits to experimentation, will supposedly be overcome soon by the progress
    of technology. New generations of transmitters, and possibly other satellite systems equipped with
    mare advanced onboard instruments, will certainly provide relevant infarmation on the many challenging
    questions related to avian migration and navigation which cannot be answered by conventional methods.
    Preliminary results from a satellite tracking experiment on migrating Brent Geese, recently run by
    the research team which the authar belongs to, are briefly reported. Despite the limited operative lifetime
    of transmitters, this method allowed us to reconstruct a large portion of the geese’ flight paths from
    their main staging sites in Iceland to the breeding grounds on Canadian arctic islands, and also to
    investigate the experimental birds’ orientational strategies.

  10. Seasonal variations in numbers and levels of activity in a communal roost of Choughs  Pyrrhocorax pyrrhocorax  in central Spain


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    19 88

    This paper presents an analysis of number and activity rates throughout year in a large
    communal roost of Choughs Pyrrhocorax pyrrhocorax in Centrai Spain. Number of Choughs attending
    the roost vari ed along the year, the greatest gatherings occurring during the winter. In the breeding
    season the roost is occupied mostly by non-breeding Choughs staying a short time in pre-roosting
    activities. Communal roosting in the area is interpreted as a behaviour related with socially organised
    foraging. After comparing variations among roosting numbers, activity patterns and duration of the
    roosting activities in the different periods of the year, we suggest that communal roosting may serve
    to facilitate mating.

  11. Homing experiments with the Domestic Dove  Streptopelia risoria


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    16 65

    A group of 4-14 months old do mesti c doves (Streptopelia risoria), which had been raised
    according to the procedures used in investigations on pigeon homing, was subjected to test releases
    at various distances (0.1 to 9.0 km) from the home loft. The results show that this tame bird species
    owns a strong homing drive which, however, is not supported by a true navigational mechanism. Good
    homing success was in fact reported only in tests carri ed out at sites where the doves had a direct view
    of the home loft , or after the birds had been given the opportunity to develop familiarity with the
    test area.

  12. Diet and nest site characteristics of Eagle Owl (Bubo bubo) breeding in two different habitats in north-eastern Greece


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    25 119

    One hundred and eighty-five pellets and prey remains of Eagle Owl (Bubo bubo) collected during
    1990-92 in north-eastern Greece, were examined to determine the owl’s food habits. The Eagle Owl took
    a wide range of prey, its diet consisting of about 59 species. The main food group was vertebrates (95.2070
    by numbers) supplemented with invertebrates (4.8%). The most important food groups were small mammals
    (48.9%) and birds (44.1 %). Game species played an insignificant role as prey in the Eagle Owl’s diet. The
    diet vari ed between habitat. In forest habitats Eagle Owls fed mainly on birds and insects, whereas in cultivated
    habitat they fed predominantly on small mammals. Eagle Owls nested on cliffs facing S-SW. The mean distance
    between neighbouring nests was 2.8 km (ranging from 2.1 to 5.5 Km).

  13. Changes in the numbers and interspecific interactions of Red Grouse (Lagopus lagopus scoticus) and Black Grouse (Tetrao tetrix)

    PARR R., WATSON A. and Moss R.

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    15 58

    Numbers of Red Grouse Lagopus lagopus scoticus and Black Grouse Tetrao tetrix fluctuated
    over the years on three Scottish moors where both lived. Black Grouse tended to peak in numbers
    at, or one or two years after, a trough in Red Grouse numbers. During interspecific disputes in the
    wild and in captivity, the smaller Red Grouse usually dominated the Black Grouse. We discuss the
    possibility that Red Grouse at high densities depress Black Grouse numbers on moorland through
    aggressive competition, and speculate whether such interactions have adaptive value.

  14. Predazione ai danni di popolazioni, trapiantate nell'Appennino pavese,di Formica lugubris Zett. ad opera del Picchio verde, Picus viridis


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    16 40

    Abbiamo valutato sotto vari aspetti i danni arrecati a popolazioni di Formica lugubris
    Zett. ad opera del Picchio verde, Picus viridis L.. Le indagini, eseguite in periodo di fine inverno del
    1992 sull’Appennino Pavese in località Monte d’Alpe (Pavia) dove il Picchio verde è svernante e le
    popolazioni di Formica lugubris di origine alpina e prealpina sono ormai insediate in modo stabile,
    hanno riguardato 5 aree boschi ve con differenti condizioni ecologiche e 128 acervi di formiche. L’attività
    di predazione del Picchio verde è stata considerata sotto l’aspetto della gravità e tipologia del danno
    subito dai formicai e del ruolo che tale comportamento gioca sulle popolazioni della specie predata.
    Si può affermare che il Picchio verde tende a contenere la proliferazione dei piccoli nidi di Formica
    lugubris che si formano durante l’estate per distacco da acervi di milioni di operaie, senza però essere
    in grado di compromettere la vitalità di queste grandi e importanti colonie di formiche.

  15. Biologia riproduttiva di una popolazione di Passera d'Italia, Passer italiae, nidificante in una "colombaia" della pianura lombarda


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    20 49

    Vengono presentati i risultati di una ricerca condotta nel 1991 sulla biologia riproduttiva
    di una popolazione di Passer italiae nidificante nella “coìombaia” di una cascina della pianura lombarda.
    L’inizio della costruzione dei nidi è compreso tra il 15 marzo e il 28 luglio. I nidi sono stati terminati
    in un tempo medio di 6,7 giorni (2-14). Tra l’ultimazione del nido e l’inizio della deposizione trascorrono
    in media 2,4 giorni (1-8). L’inizio delle deposizioni è compreso tra il 27 marzo e il 13 agosto. Nello
    stesso nido si sono avute fino a 4 deposizioni consecutive. La dimensione media della covata è 5,3
    uova (2-8), con differenze statisticamente significative tra covate e mesi. Le uova misurano in media
    mm 21,7 x 15,4 e pesano g 2,7 (n = 133). La durata media dell’incubazione è Il,9 giorni (11-15), con
    valore modale di 11, quella dell’allevamento dei pulii di 13,2 (11-17), con valore modale di 13; in entrambi
    i casi si sono rilevate differenze statisticamente significative tra covate e mesi. Il numero medio di
    pulii/covata alla schiusa è 4,4 (1-7), quello dei pulli/nidiata all’involo di 3,5 (0-7). I tassi di schiusa
    e d’involo, rispettivamente del 75,50/0 e dell’81 ,2%, sono più alti nelle covate numerose. Il successo
    riproduttivo è del 61,3%. La produttività annua per nido è in media di 7,3 pulii involati, con un max
    di 20 pulii in 4 deposizioni. I risultati evidenziano l’influenza svolta dalle condizioni meteorologiche
    sull’andamento della nidificazione e soprattutto sul successo riproduttivo.

  16. L'alimentazione del Nibbio bruno (Milvus migrans) nella Tenuta di Castelporziano (Roma)


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    14 42

    Nella Tenuta di Castelporziano (Roma) nidi fica una popolazione di Nibbi bruni (Mi/vus
    migrans) composta nel 1991 da almeno 16 coppie, e nella stagione riproduttiva 1992 da 9 coppie.
    Durante il 1991 sono state collezionate le borre rinvenibili sotto i posatoi comuni usati anche come
    dormitori e dopo l’involo, avvenuto intorno alla metà di luglio, è stato raccolto il materiale all’interno
    di 15 nidi. Le prede identificate e le relative percentuali sia numeriche che in biomassa sono mostrate
    in Tabella l: la più alta percentuale numerica é rappresentata dagli Insetti con il 39.5070,ma in biomassa
    non costituiscono che lo 0.2 % della dieta. AI contrario i Mammiferi pur essendo il 20.8% in numero,
    forniscono ben il 37.3 % della bio massa totale consumata.

  17. Breeding populations of gulls and terns in northern Egypt


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    17 60
  18. Osservazioni preliminari sulla biologia riproduttiva del Picchio dorso bianco Picoides leucotos lilfordi  in Italia Centrale


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    18 365
  19. Book Reviews

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    15 51