Biologie

During two annual cycles (from September 2012 to August 2014), we analyzed structural patterns (provided and compared data on the diversity metrics) of bird assemblages in coastal wetlands of Northeastern Algeria. Annual and seasonal differences in relative species abundance were analyzed from the viewpoint of diversity/dominance. Bird assemblages vary only in the number of species (35 recorded species during the wintering season against 23 during the breeding season). Values of the relative abundance in both seasons were similar, curves in the diversity/dominance diagram were analogous (not significantly different; both p-value > 0.05 under One-way ANOVA). Indeed, the seasonal structure of waterbird communities indicates highly dominated assemblages manifesting themselves in reduced species diversity and increased dominance of certain species. Simpson’s index was never recorded below 0.50, thus indicating evidently lower evenness. The Eurasian Coot Fulica atra and the Little Grebe Tachybaptus ruficollis were highly dominant species together accounting for more than 50% of waterbird communities. This atypical organization (highly dominated structure) is mainly due to anthropogenic or natural stresses. The marked decline in bird species diversity recorded during the study period in this study in the course of (approximately two years long) may be of concern to wetland managers as causes and consequences of the increased number of widespread species and factors behind the increasing species diversity are likely to be felt in both seasons.
Keywords.— Bird assemblages, diversity indices, widespread species, rank/abundance

Riassunto-Andamento temporale e uso complementare di una zona umida mediterranea (Tonga, Nord-est Algeria) da parte degli uccelli acquatici migranti e residenti. Abbiamo effettuato una descrizione quantitativa sull'uso di una zona umida mediterranea (Tonga, nord-est dell'Algeria) da parte di 22 specie di uccelli acquatici (11 residenti e 11 migratori paleartici) durante il periodo di fine-estate inizio-inverno, analizzando anche la loro gestione del tempo diurno e le relative principali caratteristiche del paesaggio. Le analisi delle analogie nella gestione del tempo da parte degli uccelli (analisi del clustering gerarchico) ha mostrato 4 gruppi di specie associati a 4 attività principali: nutrimento principalmente nelle ore diurne (11 specie), dormire (6), nuotare (3) e riposare (2). Le specie residenti (aironi e rallidi) hanno mostrato un tempo di nutrimento mag-giore rispetto alle specie migratorie (anatre tuffatrici, gabbiani e cormo-rani). Dal periodo di fine-estate a quello di inizio-inverno le abitudini dei migratori cambiano, mentre i residenti si comportano uniformemente durante le ore diurne e durante il corso della stagione. L'utilizzo di questa zona umida naturale in maniera complementare da parte di una gran numero di uccelli acquatici (residenti e migratori) è favorita prin-cipalmente dalla presenza di numerosi tipi di habitat. Abbiamo consta-tato che sono 3 le principali unità ecologiche più utilizzate come habitat di foraggiamento tra podicipedidae Bonaparte, rallidi, anatre, gabbiani ed aironi: corpo idrico aperto, piane tidali e prati allagati. Al contrario, vegetazione a foglie galleggianti ed emergente alta erano le categorie di habitat più comuni usate nelle attività di riposo, soprattutto da cormorani ed aironi. I dati raccolti sui requisiti di comportamento di questi uccelli acquatici possono essere utilizzati per la conservazione e la corretta gestione di questa e di altre zone umide costiere mediterranee. Parole chiave: comportamento diurno, microhabitat, metodo di coordinamento, periodo stagionale, uccelli acquatici. Abstract-We carried out a quantitative description of the use of a Mediterranean wetland (Tonga, Northeast Algeria) by 22 waterbirds species (11 residents and 11 Palaearctic migrants) during late summer-wintering period, also analyzing their species-specific diurnal time budgets and the main related features of the landscape. The analyses of similarity in time budgets across birds (hierarchal Cluster Analysis) showed four clusters of species associated with four major activities: day time mostly feeding (11 species), sleeping (6), swimming (3) and resting (2). Residents (herons and Rails) showed a higher feeding time when compared to migrants (diving ducks, Gulls and Cormorants). From late summer to winter the time budget activity change in migrants; in contrast residents behave uniformly among daytime and at the course of the season. The use of this natural wetland in a complementary way by a high number of waterbirds (residents and migrants), is principally promoted by the existing of numerous habitat types. We found that 3 main ecological units, open water body, mudflats, and flooded meadows were the most utilized as foraging habitats among grebes, rails, ducks, gulls, and herons. In contrast, floating-leafed vegetation, and tall emergent vegetation were the commonest habitat categories used in resting activities especially by cormorants and herons. Data on behaviour requirements of these waterbirds can be used for conservation and correct management of this and other Mediterranean coastal wetlands.

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The Black Kite Milvus migrans is a common species in northeast of Algeria. Data on the breeding ecology and biology of this bird was well collected all over the world, but in Algeria the population of Black kite are still not known. This study was carried out during 2015 at Ras El Ma ravine (Guelma, northeast of Algeria) in order to characterize the phenology and biology of the breeding of this raptor. The breeding population of black kite was present from March to September with a peak of 28 individual noted at the first week of August. The egg-laying started from April. 36 nests of black kite were surveyed during the breeding season. The first chick had fledged from July 16 th. A total of 15 eggs were measured during our study the mean egg length, breadth, weight and volume were 55 ± 2.33 mm, 43 ± 2.11 mm, 103.66 ± 1.2 g, 51.76 ± 1.2 cm 3 respectively. The clutch size of the black kite varied between 1 and 3 eggs.