Residues of mercury, lead, cadmium and chromium in eggs of five species of birds nesting in Lombardy (Italy) in 1990. In spring 1990, we collected and analysed a total of 95 eggs of five species of birds nesting in Lombardy, in order to identify and quantify levels of contamination with mercury, lead, cadmjum and chromium. The five species were Mallard Anas platvrhvnchos, Blackbird Turdus merula, Moorhen Gallinula chloropus, Hooded Crow Corvus corone cornix and Domestic Dove Columba livia domestica. The eggs were measured and weighed and correlations between concentrations and both eggshell index and egg volume were investigated. Significant correlations were observed only in Hooded Crow and Domestic Dove; un Hooded Crow, between mercury and eggshell index (P<0.00 1), between mercury and egg volume (P<0.00 1), between lead and eggshell index (P<0.02), and between chromium and eggshell index (P<0.05); and in Domestic Dove, between lead and eggshell index (P'0.02) only. For both these species, the correlation between lead and eggshell index was negative (similar to the known correlation with DDT and its metabolites); the other correlations were positive, but these must be further venfied. Mercury levels were higher in eggs of Moorhen ( xav.= 0.175 µg/g w.w.) than in those of other species. Cadmium and lead were present in trace amounts in all five species; these amounts may however be toxic, particularly where there is a dietary calcium defíciency which may lead to increased uptake of these metals. Domestic Dove and Mallard showed somewhat higher levels of chromium than in Moorhen, Hooded Crow and Blackbird. The toxicological implications of the levels of metals found in the sampled eggs have yet to be identified. The toxicity of these metals may be amplified in the presence of other contaminants and stress factors (eg. food shortage, cold). Further studies are needed to investigate the importance of eggs as a route for the excretion of metals in birds exposed to chronic intoxication.

The Bittern population of a marshland in Central Italy was censused using a network of listening stations. This technique appears to be sufficient to quantify the population being examined, but does not allow an accurate analysis of the positions of the booming males. The data in the literature, dating from 1974, indicate that the population studied had a progressive increase up to the early 1990s (from 0-1 to 14-18 males) and then a phase of decline (with 7-9 in 1994). These vanations seem mainly due to the changes in the marsh vegetation. This was positive at first, thinning out the reedbeds, then negative with their progressive reduction. However, the role of primary importance of the studied population in Italy has been confirmed

The Alpine Chough Pyrrhocorax graculus is a social corvid which uses food provided by tourist activities in mountain regions (e.g. at ski stations, refuse dumps, picnic areas). In order to determine the impact of the human food supply on the Alpine Chough, foraging flock size and distribution were studied in a tourist region in the Northern French Alps bet veen 1988 and 1992. Alpine Chough attendance at tourist sites was closely related to human activities. Activity rhythm was influenced by human presence on picnic area in summer. Relations to human activities held at a seasonal scale (such as opening of a ski station) but not at a daily time scale (such as weekend). Long term trends of Alpine Chough populations since intense tourist development at altitude are discussed with regard of flock size counts recorded at a same site before and after intense tounst development.

FABRIZIO GRIECO

The phenology and structure of the nest-sites of a Cormorant colony in dead trees, during 1992-1993, are described. Sites were classified using three criteria: (1) topography of the colony; (2) density of breeding trees; (3) structure of breeding trees. Photographs were used to mark the nests during the breeding penod. The number of nests increased to a peak in early May and then declined; many nest sites were used successfully by more than one pair. The structure of nest sites was more important than their position. The percentage of sites reaching the nest stage decreased dunng the breeding season. Adult birds showing much white on the head are more frequent in the centre ofthe colony. Sites taken by breeding immature-plumaged birds are like those taken by adults, but immatures seem to succeed in building nests and breeding only on sites of lower quality. Beginning from 1992 some breeding attempts occurred on sites outside the present colony. Current level of competition between Cormorants and Grey Herons which breed in the same area is low. Differences between this and a similar German colony are discussed.

SALLY WARD

Deparlment of Biological and Molecular Sciences, Universitv of Stirling, Stirling, FK9 4LA, U. K. Address for correspondence: Department of Zoology, Universitv of Aberdeen. Tillvdrone Avenue, Aberdeen, AB9 2TN, U K

Relationships between egg mass, egg composition, hatchling mass, female characteristics and environmental conditions during egg formation were investigated for Swallows Hirundo rustica in Central Scotland. Egg dimensions were highly correlated with egg mass. 60% of variation in egg mass originated from differences between females. Egg mass was repeatable (repeatability=0.54) for individual birds but was not related to other female characteristics such as measures of structural size. Egg mass was not related to clutch size, hatchability or position in the clutch. Eggs contained more lipid if favourable environmental conditions prevailed dunng egg t'ormation. Heavier eggs contained more lipid and lean dry component. A sample of eggs was hatched in a incubator so that hatchlings could be matched with the eggs from which they emerged. Egg mass explained 60% of vanation in hatchling mass, 79% of vanation in hatchling mass was explained by the first component in a principal component analysis which used egg mass, length and breadth to describe egg size. Heavier eggs produce larger hatchlings which generallv grow faster and have greater survival across 34 studies of non-passerine birds. Although larger passerine eggs produce hatchlings which are initially larger and grow faster (n=7 studies) this does not lead to increased survival. Hirundines lay relatively small eggs for their body size although production of larger eggs was predicted to have little extra cost for a Swallow and should be advantageous as larger hatchlings would be more likely to survive periods of food shortage.

The off-nest behaviour of the Little Tern Sterna albifrons was studied in the Axios Delta, a Macedonian wetland. The time taken up by the following components of this behaviour was measured during incubation in four nests and during different parts of the day. Away from nest, Shift dunng incubation, Chase of intruders, Throwing Sideways, Around nest, Wake Up and fly, Courtship Feeding and Human Disturbance. Data were analysed by Repeated-Measures ANOVA. There were significant effects of nest, day and part of the day on a number of these components of off-nest behaviour. The birds from one of the nests spent very
different proportions of time on the various activities than those at the other nests. The effects of the part of the day were clear and some activities exhibited trends: time spent on Away and Shift typically decreased from the beginning to the end of the day, Human Disturbance was diminished in the third part of the day and Wake Up and Throwing Sideways were greater in the middle of the day. Despite clear day effects on many variables there was no regular pattern to these. There was also an interaction of day and part of the day on Away, Throwing Sideways, Human Disturbance and Wake Up denoting that these activities were affected by unpredictable events.

The method normally used to measure the wing shape in both iive birds and museum skins, is based on the measurement of the distance between the tip of each primary and the tip of the folded wing. This method has two essential shortcomings: it does not allow to compare live birds with museum skins and it is difficult to standardise when different observers are involved. It seems therefore inadequate for studying the wing shape variation of populations breeding on a large geographical range. Here we propose to use the total feather length for measuring the wing shape. This will allow to compare living birds with museum skins and to obtain comparable results from different ringers.

A test on the accuracy reached by 13 unexperienced trainees introduced to two different methods for the measurement of wing-length (maximum chord MC, feather length P8) was performed during a 5-days ringing course on 203 Swallows Hirundo rustica and 63 Reed Warblers Acrocephalus scirpaceus. The two measurements were standardized, and the absolute differences between the values obtained on a same bird by trainer and trainee calculated for both methods were statistically tested. In both species the feather length method produced trainee measurements significantly closer to those obtained by trainers than maximum chord. Since 1992, the feather length method is the one recommended by the Italian Ringing Centre for wing measurement in Passennes.

MASSIMO PANDOLFI

La difesa di piante con frutti che costituiscono una risorsa alimentare in situazioni di carenza di cibo risulta un comportamento abbastanza comune in diverse specie di turdidi in Nord Europa. Nel presente lavoro sono stati analizzati casi di difesa a breve termine di risorse alimentari di Capinera su frutti di Diospyros kaki. La difesa è stata osservata nel 1993 e nel 1994 ed effettuata sia da un maschio che da una femmina contro diverse altre specie di passeriformi anche se in maniera più accentuata con conspecifici, con diverse modalità: pattugliamento, attacco con picchiate, attacco con scontro fisico. Questo comportamento è attuato da un singolo animale che difende un albero-dispensa. Questa modalità di difesa, proprio perche temporanea, risulta meno accentuata in ambiente mediterraneo, meno estremo e con maggiori risorse invernali disponibili, che non nel Nord dell'Europa.