Volume 28 - N. 1
Aggression and microhabitat segregation among nesting common terns Sterna hirundo and Mediterranean gulls Larus melanocephalus
Canova L., Fasola M.Abstract Read Article Download17 34
We studied aggressive behaviour in a mixed colony of Mediterranean gulls and common terns. The two species bred syntopically but selected different reproductive microhabitats. Common terns were more aggressive than Mediterranean gulls, and aggression rate was higher towards heterospecifics than conspecifics. In both species, aggression rates were higher during the incubation phase, fell to a minimum when chicks rested in nests and increased again when chicks were able to wander inside the colony. High aggression rates during the pre-hatching phase are in agreement with theories of parental investment, while those involving adults during the chick wandering phase could be explained by a higher encounter rate with non-familiar adults, that induced an increase of aggressions between territory holders. The lower aggression in the “early chicks” phase can be explained by the increased food demand by chicks and the consequent reduction of adult density foraging out of the colony; however, selection of differing reproductive microhabitat can be considered as a further factor promoting coexistence, enhancing chicks survival immediately after hatching.
Characteristics of black kite Milvus migrans nest-trees in two Italian colonies
Zocchi A., Lacroix L., Bianchi M., Battisti C.Abstract Read Article Download19 39
Black kites often nest on trees, but little information is available on the characteristics of trees used for nest building. In this study we analysed several tree parameters that may affect tree choice, using data on 53 nests from two Italian colonies. Black kites preferred to build their nests on “chandelier type” branch platforms located at approximately 70% of relative tree height (i.e. regardless of the absolute tree height), and used stable trees, as evaluated using a stability index (tree diameter/tree height). In both study areas, oaks Quercus spp. appeared to be more likely to meet all these criteria, though nests were also located on other tree species with similar characteristics.
Biologia riproduttivadella cannaiola Acrocephalus scirpaceus in una zona umida dell’Italia Centrale
Quaglierini A.Abstract Read Article Download21 38
Breeding biology of reed warbler Acrocephalus scirpaceus in Central Italy. During twelve years (1999-2003), a study
was carried out on the population of reed warbler Acrocephalus scirpaceus nesting in the Lake of Massaciuccoli, a large marsh in
Central Italy. Data about location of nest and main reproductive parameters were collected. Reed warblers locate nests in pure reedbeds, upon young or two-year old stems. Nests are fastened to 3.5 stems on average, 91 cm above water surface and 32 cm far from
open waters. Below nests, water is 15-cm deep on average, and reed density is 830 stems/m2. Nests are fixed to stems 231-cm high
and 0.41-cm large. The complete clutch averages 3.5 eggs, a value lower than those reported in literature. Double brooding is a
common feature, with first broods layed between May 4th and June 21th, and the second ones occurring between June 13th and August
8th. Hatching rate was 76.8%; and 82.8% of nestlings fledged successfully (1.95 fledged youngs per nest) for an overall reproductive output of 63.6%. No nestlings have been raised in 23.3% of checked nests. Although territories of the reed warbler are 440-
m2 wide on average, the estimated total density in reed beds was 261 pairs/km2; thus a large part of suitable habitat for reproduction was not used. The breeding population is not decreasing, despite the general decay of the environment, because, contrary to
great reed warblers, reed warblers are able to use also ecotones and intermediate-aged reed beds.
Occupancy rate and habitat variables influencing nest-box use by tawny owls Strix aluco
Sacchi R., Galeotti P., Boccola S., Baccalini F.Abstract Read Article Download19 48
Nest-box use by owls was examined in a large urban park northeast of Milano (northern Italy) from 1997 to 2000. Nestbox features and several micro- and macrohabitat variables were compared among the 89 sites which held a nest box for at least
two years consecutively. Sites were classified according to the use of the nest box they held: unused, used for roosting and used
for breeding. The percentage of used nest-boxes increased significantly over the four years of study, being on average 44%, but
only a small fraction (12%) were used for breeding. Nest-box use was higher during winter than during both summer and autumn,
suggesting that thermal benefits might affect nest-site selection by tawny owls. Used nest-boxes were located higher on trees and
were settled in younger wood patches than unused nest boxes. Tawny owls appear to prefer natural cavities to artificial nests for
breeding in our study area, while out of the breeding season nest-boxes are often used as shelters. The preference for nest-boxes
higher than 6 m suggest that Tawny owls might select higher nest-boxes as a part of a protection strategy against human disturbance, which is very high in the Park of Monza.
Partial albinistic cases in adultand juvenile Cory’s shearwaters Calonectris diomedea
Ristow D., Witte L.Abstract Read Article Download11 39
Osservazioni di albinismo parziale in berta maggiore Calonectris diomedea. In questa nota riportiamo due osservazioni di albinismo parziale in berta maggiore. Il primo caso riguarda un maschio adulto, che ha mostrato una singola timoniera albina per almeno 4 stagioni riproduttive consecutive. Il secondo concerne un pulcino (femmina) al nido, che presentava un’ampia
distribuzione asimmetrica di remiganti e copritrici depigmentate su entrambe le ali.
Osservazioni sulle modalità della migrazione primaveriledei rapaci a Capo d’Otranto
Premuda G., Mellone U., Cocchi L.Abstract Read Article Download20 45
Spring raptor migration routes at Capo d’Otranto (Apulia, Southern Italy). Capo d’Otranto is one of the most important sites for monitoring spring raptor migration in Italy. Despite this, migratory routes over the Otranto Channel are not completely clarified. During a preliminary survey in April 2002, we detected a new watch-point for monitoring raptors migrating both northwards, up the Italian peninsula, and north-eastwards, across the Adriatic Sea towards the Balkans. This point also allowed us to check for possible migration routes over the Otranto Channel, from the Balkans towards Italy. Between 20 and 29 April 2003, 441 raptors were recorded: 17.2% of them (76 individuals) crossed the Adriatic Sea, while the others (82.8%) migrated up the coast. We did not observe any bird coming from the Balkans. The observations reported do not confirm hypotheses of migrating raptors
coming from Balkans and of migration pathways from Albania and Greece. The new watch-point allows for closer views of migrating raptors and easier species identification, particularly the lesser kestrel Falco naumanni. As such, it has emerged as a very important site for monitoring the spring migration of this species.
The autumn migration strategies of adultand juvenile short-toed eagles Circaetus gallicus in the central Mediterranean
Agostini N., Baghino L., Panuccio M., Premuda G., Provenza A.Abstract Read Article Download21 34
Le strategie di migrazione autunnale di adulti e giovani di biancone Circaetus gallicus nel Mediterraneo centrale. Durante la migrazione autunnale, i bianconi nidificanti in Italia centrale utilizzano una rotta “ad arco”, attraversando il Mediterraneo sullo Stretto di Gibilterra. Inizialmente questa rotta prevede una migrazione verso NNW, lungo il versante occidentale dell’Italia centrale. In questo studio abbiamo analizzato la migrazione autunnale del biancone nelle Alpi Apuane (Italia centrale), in relazione alle differenti classi di età. Nel periodo 15-26 settembre 2001 sono stati contati 351 individui in 108 ore di osservazione, ed è stato stimato il passaggio di 272 adulti, 23 immaturi e 56 giovani. I bianconi tendevano a migrare in gruppi, comprendenti in media 3.5 individui (N = 77 gruppi); almeno in 17 casi i gruppi contenevano sia adulti che giovani. La bassa percentuale di giovani riportata sulle Alpi Apuane, unitamente al tardivo passaggio di decine di questi attraverso il Canale di Sicilia, sembra suggerire che solo parte dei giovani appartenenti alla popolazione nidificante in Italia centrale apprenda la rotta “ad arco” seguendo gli adulti.