SEASONAL BODY MASS CHANGES IN PIED FLYCATCHER (FICEDULA HYPOLEUCA) AT TWO STOPOVER SITES IN MOROCCO

Souad Zerdouk, Houda Hadi, Abdelaziz Benhoussa and * Hamid Rguibi Idrissi. Laboratory “Biodiversity, Ecology and Genome”, Center of Research “Plant Biotechnology, Microbial, Biodiversity and Environment” University Mohammed V, Faculty of Sciences, Rabat, Morocco. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History Received: 15 May 2019 Final Accepted: 17 June 2019 Published: July 2019


ISSN: 2320-5407
Int. J. Adv. Res. 7 (7), 479-486 480 species winter in Morocco, and it is predicted that their body mass will be lighter in autumn, after arrival, than in spring, before setting off for their breeding grounds.
Study of mass change at many stopover sites may help to study the difference migration strategies between species. Some data suggest that migration strategies my be considerably different even in closely related species of passerines migrants (Bibby and Green, 1981;Ellegren, 1990Ellegren, , 1991Schaub andJenni, 2000, Casimir et al., 2003;Rguibi et al., 2003) with variation in the time period and location at which maximum fuel loads accumulated (Gargallo and al;, 2011).
In this paper, we analyze body mass and feeding ecology in a long-distance migrant, the Pied Flycatcher Ficedula hypoleuca, during autumn and spring migration. The data were collected by captures in nets at two stopover sites in Morocco : reed bed in Larache (Atlantic coast) and Kebacha (Mediterranean coast) ( fig. 1), in several years (nine season-year-site combinations). The main aim was to compare the body mass variation between seasons, sites and age-classes and to describe the diet in terms of prey composition to further interpret these data in relation to migration strategy during the stopover in Morocco.

Data set
In both localities, the nets were concentrated in a limited area where capture effort was thus maximized. Birds were identified to the species level, banded with a numbered aluminium ring (Helgoland rings, Wilhelmshaven, Germany), weighed to the nearest 0.1 g with a Salter spring balance (60 g), and their wing chord measured to the nearest 1 mm (Bairlein, 1995). The amount of subcutaneous body fat was estimated on a scale of 0 (no visible fat on the abdomen or in the furculum) to 8 ( fat bulging both on the abdomen and the furculum) (Kaiser 1993). Most individuals were aged, separating birds in their first years (Svensson, 1992, Jenni andWinkler, 1994).
Some individuals were administered a 1% solution of antimony potassium tartrate, according to the method of Poulin and Lefebvre (1995). The solution was made one month before sampling to reduce the toxicity of the chemical. On the other hand, only the birds captured over two hours after sunrise were forced to regurgitate. Treated birds were given 0.08 ml of solution per 10 g body mass through a 1.5 m diameter flexible plastic tube attached to a 1 ml syringe. The chemical was then slowly administered, and the bird placed in a small dark box lined with absorbent paper. Birds were released 20-30 minutes later, and regurgitated items were preserved in 70% ethanol.
For the analysis of body mass and fat reserves, we tested for differences in these variables between seasons (spring and autumn), sites and age groups, using the General Linear Model (GLM). Diets characteristics were compared between sites by means of classical statistical tests (Likelihood ratio G-tests, ANOVAs).
A total of 461 individuals pied flycatchers were trapped, and the totals for each site and age groups are show in Table 1. 481 Results:-

I. ANALYSIS OF POPULATION WEIGHT
The mean body weight of the whole sample was 13.66g±1.39 (n = 338) and ranged between 10.0g and 17.3g during autumn migration, and 12.21g±1.25 (n= 123) and ranged between 9.90g and 18.30g during spring migration. The results of the analysis of variance of the weight in two stopover sites appear in Table 2.
An analysis of variance (Table 2) demonstrates that age, although a significant factor, juvenile birds appear little heavy than the adults. Moreover, results from analysis of variance revealed that only body mass and age and site were significantly related to the date of passage (Table 1). There was a considerable season effect on body mass, with individuals weighing on average 1.07 g more in autumn than in spring (Table 2). Adults tended to be heavier than juveniles (main effect of age: +0.1 g for adults vs. first year) across sites and seasons, but a significant season x site interaction indicated that birds of all ages were able to gain weight at an unaffected rate and that arriving or departing birds had different weight during migration (Fig. 2).
Body mass and fat reserves all increased markedly during the day since first capture ( Table 2). These changes in body mass were strongly associated with the observed changes in fat reserves (Fig. 3).

II. POTENTIAL PREY ABUNDANCE
In total 129 and 250 food items were identified in the 26 and 15 emetic samples selected at reed bed in Larache and Ramsar Smir, respectively from across the season. A comparison of the relative proportion of the major invertebrates-groups identified differed significantly between the two sites (t-test for unequal variances: t= 3.83, df = 17, p = 0.001) suggesting differences in food intake between sites. The prey size (ranged between 2.5 and 7.5 mm) distribution differed significantly between the two site (G = 2.512, df = 4, p = 0.05) with birds at reed bed in Larache fed larger prey than at Ramsar Smir.

Discussions:-
The body mass of the individuals birds can vary widely during migration (Blem, 1990). Many theoretical analyses suggest that this variation reflects the differences between the costs and benefits of fat storage (McNamara and Houston, 1990;Houston and McNamara, 1993).
Our data demonstrated that autumn birds of Pied flycatchers captured at two stopover sites were able to accumulate body mass (fat stores) faster during the day than spring birds. Several hypotheses may explain why spring migrants gained mass at a somewhat slower rate than autumn birds. First, the duration of the stopover in autumn migration leading to reduced selective pressure for short stopovers and rapidly body mass gain (Burger 1988; Wunderle 1991; Rguibi Idrissi et al,. 2003), or, the competition potential among individuals juveniles and adults during stopover at two sites, forcing some birds to use less favourable habitats at each site resulting in lowered rates of mass gain. In the other hand, we have found in our research on the Reed warblers (Rguibi Idrissi et al., 200;2004;2007) that variation of stopover and foraging patterns was age-related. Stopover duration was longer for juveniles than for adults and longer in autumn than in spring. Adults tended to be heavier than juveniles across sites and seasons.
The rate of body mass varied among site, seasons and age-groups. The rate of mass estimated based on the slopes of the regressions between body mass and capture time (Fig. 2) may estimate the mass change because many migrants were probably rehydrating after nocturnal flight and therefore appeared to be gaining mass more rapidly than they actually were. Body mass differences between adults and juveniles birds were usually small but apparently sufficient enough for birds to base stopover decisions on. Similar age-specific differences in body mass occurred in Pied flycatchers in Spain (Veiga, 1986), Sedge warblers in Northern Italy (Spina and Bezzi ,1990), Bluethroats in Sweeden (Ellegren, 1991) and Reed warblers in Morocco (Rguibi Idrissi et al., 2003). Is likely that these differences reflect different migration strategies in autumn and spring, together with geographical influences, fattening strategy (Rogers, 1987) and predictability of their food resource. Indeed, during migration, birds respond to decreased food availability by increasing body mass and energy reserves (Biebach, 1990;Bairlein, 1991;Rogers, 1995;Witter et al., 1995;Witter and Swaddle, 1997;Chernetsov and Titov, 2000), moreover, birds can reduce body mass and energy reserves under increased risk of predation (Witter et al., 1994). Generally, migration strategy assumes that there is a negative relation between stopover, variation of body mass and fatting rate (Bairlein, 1990(Bairlein, , 1998Alerstam and Lindeström, 1990). The differences in body mass of pied flycatchers between sites could be attributed to a declining availability of food between sites and between age-groups the mass loss could be due to low post-fledging foraging 482 efficiency. The foraging strategy of pied flycatchers during autumn migration shows that birds in Atlantic site exploit a greater diversity of prey of large size than in Mediterranean site which birds fed on small prey. However, the manipulations of food availability influenced either absolute levels of body mass or the pattern of change mass during the day of capture. This explains the variation rate of body mass between season and age-groups at both sites, although less pronounced at the Atlantic site.    Table 1. Total number of juvenile and adult Pied flycatcher trapped during stopover at two sites in Morocco.