Sylvia Melanocephala Research Articles

Hippocampal volume in migratory and non-migratory warblers: effects of age and experience

We tested the hypothesis that experience of migration from Europe to tropical Africa by Garden Warblers is associated with changes in the relative volume of the hippocampus, a brain region thought to be involved in processing spatial information, including that used in navigation. Relative hippocampal volume was larger in birds at least one year old that had migrated to and from Africa, than in naive birds approx. 3 months old. Further comparisons between groups of differing age and experience of migration suggested that both experience and age during the first year have an effect of relative hippocampal volume. The increase in relative hippocampal volume was mainly due to a decrease in the size of the telencephalon; however, the comparison between young, naive birds and older, experienced birds also suggests a possible increase in absolute hippocampal volume. The latter is associated with an increase in number and density of neurons, whilst the former is associated with an increase in density but no change in total number of neurons. In a non-migratory close relative of the garden warbler, the Sardinian warbler, older birds had a smaller telencephalon but there was no change in hippocampal volume, which supports the view that changes in the hippocampus may be associated with migratory experience, whilst changes in the telencephalon are not.

Remoult of tertials during post‐juvenile and post‐nuptial moult in Sardinian Warblers (Sylvia melanocephala)

Remoult of tertials during post‐juvenile and post‐nuptial moult in Sardinian Warblers (<i>Sylvia melanocephala</i>)

Identity, prevalence and intensity of infestation with wing feather mites on birds (Passeriformes) from the Setubal Peninsula of Portugal

The results of a 4 year project investigating species of mites infesting wing primary feathers on 21 species of Passeriformes are reported. The majority of species were identified as belonging to the genus Proctophyllodes Robin, 1877 with one new host record. In addition Pteronyssoides obscurus Berlese 1884 was found on European swallows, also a new host record. A novel method to enable quantification of mite intensities without causing harm to the birds was devised and evaluated. This relied on visual inspection of wing primary feathers and assignment of subjective infestation scores to individual feathers, the sum of the individual scores comprising the primary feather total mite infestation score (PTMIS). Comparisons between species revealed that birds could be grouped into four categoris depending on their infestation intensity with mites. Swallows, sand martins and greenfinches showed the highest prevalence and most intense infestations (mean PTMIS ≥ 6.8). Blackbirds, blackcaps, serins, goldfinches, Cetti's warblers, great tits and house sparrows showed moderate levels of infestation with prevalence in the range 60–90.9% but a mean PTMIS lower than in the former group (1.6–5.8). The third group comprised Sardinian warblers, nightingales and short-toed tree creepers and was characterized by a prevalence of mites ≥ 40% and a mean PTMIS of 0.6–1.4. The final group, representing wrens, chiffchaffs, fan-tailed warblers and waxbills were without detectable mites, the only exception being wrens on which mites were identified in only three birds of the 32 sampled. These results are interpreted in the light of published information and possible explanations for the observations are discussed.

Factors involved in the distribution of forest birds in the Iberian Peninsula

The relationships between a series of environmental variables and the abundance of individual species of forest birds were examined in 58 large woodlands along a band crossing the Iberian Peninsula from north to south. The variables were mean annual rainfall, mean annual temperature, density of trees <20 cm in diameter, density of trees >30 cm in diameter, floristic composition (conifer or broadleaved trees) and geographical situation (distance from northern extreme of study band). The variable most highly correlated with bird density was mean annual rainfall (40% of the species had significant partial correlations with this parameter). The northern species (Chiffchaff, Goldcrest, Robin, Song Thrush, Bullfinch, etc.) generally correlated positively with mean annual rainfall, while the Mediterranean species (Sardinian Warbler, Bonelli's Warbler, Black-eared Wheatear, Rock Sparrow, Spotless Starling, Azurewinged Magpie, etc.) exhibited an inverse pattern. Mean annual temperature (36%) was also closely associated with bird distribution, but did not show clear tendencies according to biogeographic groups. Floristic composition (26%) was a strong determinant of the abundance of species distributed throughout the whole Iberian Peninsula and geographical situation (22%) largely determined the distribution of the northern and Mediterranean species. Finally, density of trees <20 cm in diameter (20%) and >¸30 cm in diameter (14%) generally showed a negative association with the majority of the species, particularly the Mediterranean species.

IMPROVISATION OF NEW NOTES DURING SINGING BY MALE SARDINIAN WARBLERSSYLVIA MELANOCEPHALA

ABSTRACT The songs of Sardinian warblers Sylvia melanocephala are extremely complex and variable, and even consecutive songs uttered by the same male usually differ. To provide a better understanding of the nature of the variation recorded, an attempt has been made to determine size and composition of the note repertoire of three selected individuals. The analysis was carried out on samples each consisting of several dozen songs, and the various notes were sorted on the basis of the visual similarity of their spectrographs patterns. Each male turned out to have a very large note repertoire which does not show any overlap with those of other males, with the only exception a particular note found in the songs of all the males. In two birds out of three, however, the graphs of the occurrence of new notes in consecutive songs show no tendency to become asymptotic. This suggests that the assessment of note repertoire size in these birds is not accurate, as they continue inserting new notes in their songs even after they ha ve uttered several dozen songs. A table recording the presence or absence of the various notes in consecutive songs revealed that at least two of the three birds used different sets of notes in different bouts of songs, switching from one to another after short pauses made between two consecutive bouts. All this makes the attempt to assess the actual size of the note repertoire in these birds very difficult, and makes it probable that Sardinian warblers do not possess a finite repertoire of notes. The pattern of note selection observed for the three males in this study is best explained by assuming that these birds improvise new notes as they sing.

Determining the age of Sardinian Warblers

Determining the age of Sardinian Warblers

Weitere Indizien für „sektorale“ Handschwingenmauser bei jungen Singvögeln

The occurrence of sectoral postjuvenile primary moult is confirmed for Sardinian Warbler, Greenfinch, Goldfinch and Red Crossbill and is newly described for White Wagtail, Siskin and Cirl Bunting. A characteristic feature for this type of moult seems to be that the primary coverts belonging to the renewed primaries are not at all or irregularly moulted. It is supposed that sectoral primary moult is provided in the moult programme of many passerines but is only manifested under special conditions. One of these is an early hatching date.

The Macaronesian bird-flower element and its relation to bird and bee opportunists

Canarina canadensis, three Isoplexis species and Lotus berthelotii, among other species, have been supposed to be bird pollinated. None of their flowers reflect UV light and the volume of nectar produced is relatively high with low sugar concentration, indicating bird pollination. This study gives the first report of birds visiting and thus pollinating these species. Sylvia melanocephala, S. conspiciltata and Phylloscopus collybita visited I. canariensis and C. canariensis flowers. Isoplexis sceptrum and Digitalis obscura are regarded as transitional species anthecologically between I. canariensisj I. isabelliana and European Digitalis species.

A Study of Avian Frugivores, Bird‐Dispersed Plants, and Their Interaction in Mediterranean Scrublands

Fruit production and patterns of seed dispersal by birds were studied at two elevations in the mediterranean scrublands of southern Spain. Fleshy—fruit—producing species represent a very prominent fraction of woody plants in terms of cover (57—76%) and species number (49—66%). Fruit production occurs year round in the lowland site but is confined to August—February upslope. Ripe fruits are most abundant (&gt;105 ripe fruits/ha) in November—December. Fruit abundance fluctuates widely between years at the highland locality but only slightly in the lowlands. In both communities, the dominant species ripen fruits in autumn—winter, display the highest within—plant fruit densities, and tend to have the most lipid—rich fruits. Fruits differ in pulp nutritive value, seediness, and relative amount of pulp among species but are remarkably uniform in size (mostly 5—10 mm transverse diameter). Two—thirds of the passerine species at each site eat some fruit. Of these species, 69% (highland) and 26% (lowland) are resident "fruit predators," feeding on either pulp or seeds alone, and damaging the seeds when eating pulp and seeds together. The rest are overwintering or migratory seed dispersers that ingest whole fruits without damaging seeds. Seed dispersers are most common in late autumn—winter, coincident with the peak in fruit abundance and the predominance of lipid—rich fruits. A few small (12—18 g body mass) disperser species (Erithacus rubecula, Sylvia atricapilla, Sylvia melanocephala) account for most of the frugivory at each site and disperse the majority of seeds. Fruit predators either are relatively scare or eat fruits infrequently, or fruits represent a negligible fraction of their diets. Fruit removal was very high (89—100% of crops) among species with fruits smaller than the gape width of the abundant small—sized dispersers, and very low among species with fruits larger than gape width. Removal success was negatively correlated with fruit size among species having fruits smaller than dominant dispersers' gape width. No relation has been found between removal success and fruit quality, fruiting time, ripening rate, or within—plant fruit density. The principal dispersers at each site ate mainly the most nutritious fruits, although not to the exclusion of less nutritious fruits. Substantial pairwise plant—bird reciprocity is not common. (The avian species disperses a substantial fraction of a plant's seeds, which in turn provide the bulk of the bird's energy supply.) Current bird—plant seed dispersal interactions are the result of evolutionary, climatic, and geographical factors in the Mediterranean. Mutualistic congruency largely is, in these cases, an epiphenomenon of these factors, not resulting necessarily from mutual adaptations (coevolution). It is suggested that actual coevolution involving a smaller set of bird and plant species may facilitate the persistence of noncoevolving (or very slowly coevolving) plant species, thus favoring the existence of a chronic "anachronism load" (with regard to dispersal) in the plant community.

Beeren und Farbenwahl durch Vögel

Three chance observations on colour preference in birds feeding on berries are presented. Blackbirds (Turdus merula) in Bavaria fed in a cherry-tree irrespective of the colour of the cherries. They began feeding when the first cherries ripened and turned from greenish-yellow to light red. As the cherries were offered in different colours at the same time, and pell-mell in the same tree, the birds presumably quickly learned by trial and error to eat cherries of different colours. A little later Blackbirds, which must have been partly if not exclusively the same individuals, started to feed on red currants. Red and white currants were offered to them at the same time, and side by side but on different bushes. In this case there was a very clear spontaneous selection of red in preference to white. White berries were only eaten after the red bushes had been cleared up by the birds. Sardinian Warblers (Sylvia melanocephala) in Sardinia, feeding on berries ofRhamnus alaterna, which are coral red and hard when unripe and turn to blackish and soft getting ripe, prefered the black ones. It is presumed that they conditioned themselves to black and soft by trial and error learning. Generalisations as to birds preferring certain colours in berries they feed on can not be drawn from any special case.

Species 39. Cisticola Tinniens. Pl. XIV.

A smallish, rather slender‐built bird; quite a typical Cisticola like subruficapilla, which species despite its different coloration is‐one of if not the nearest of its allies, about the same size, build and proportions as the Sardinian Warbler (S. melanocephala) and with much moreover in its behaviour which recalls that and other quite differently coloured bush‐loving Sylvia Warblers, such as, for instance, the Whitethroat (S. communis).

Species 39. Cisticola Tinniens. Pl. XIV.

A smallish, rather slender‐built bird; quite a typical Cisticola like subruficapilla, which species despite its different coloration is‐one of if not the nearest of its allies, about the same size, build and proportions as the Sardinian Warbler (S. melanocephala) and with much moreover in its behaviour which recalls that and other quite differently coloured bush‐loving Sylvia Warblers, such as, for instance, the Whitethroat (S. communis).