Breeding ecology of the Cattle Egret (Bubulcus ibis) in Guerbes-Sanhadja wetlands of Algeria

Regional Studies in Marine Science 33 (2020) 100979

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Breeding ecology of the Cattle Egret (Bubulcus ibis) in Guerbes-Sanhadja wetlands of Algeria ∗

Sophia Metallaoui a,b , , Hamdi Dziri a,b , Abderazzak Bousseheba a,b , Salim Heddam b,c , ∗∗ Haroun Chenchouni d,e , a

Department of Natural and Life Sciences, Faculty of Sciences, University of 20th August 1955, Skikda 21000, Algeria Research Laboratory on Interactions of Biodiversity, Ecosystems and Biotechnology ‘LRIBEB’, University of 20th August 1955 Skikda, Skikda 21000, Algeria c Department of the Agronomic Sciences, Faculty of Sciences, University of 20th August 1955, Skikda 21000, Algeria d Department of Natural and Life Sciences, Faculty of Exact Sciences and Natural and Life Sciences, University of Tebessa, Tebessa 12002, Algeria e Laboratory of Natural Resources and Management of Sensitive Environments ‘RNAMS’, University of Oum-El-Bouaghi, Oum-El-Bouaghi 04000, Algeria b

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Article history: Received 30 May 2019 Received in revised form 25 November 2019 Accepted 5 December 2019 Available online 16 December 2019 Keywords: Cattle Egret Bubulcus ibis Brood Nesting ecology Nest site use Breeding success Guerbes-Sanhadja wetlands Nest placement

a b s t r a c t Information about breeding ecology and nest site selection in the Cattle Egret (Bubulcus ibis) at newly established colonies are still lacking in many North African heronies. This study aimed at determining nest site selection and assessing breeding parameters of Cattle Egrets nesting, for the first time, at the Ouajaa marsh in Guerbes-Sanhadja wetlands (northern Algeria) in relation to nest site and nest traits. Breeding chronology of Cattle Egret in the region was monitored onsite, since the use of the wetland as a dormatory till the end of the breeding season. Egg morphometrics (length, breadth, weight and volume) and breeding parameters (clutch size, hatching, fledging and breeding successes) were measured and compared between nests built on different tree species (Salix alba and Acacia cyanophylla) and at different locations within crowns of nesting trees. The effects of nest site characteristics (nesting height, trees and positions) and nest traits (nest surface, outer and inner diameters) on breeding parameters were investigated using generalized linear models (GLMs). The breeding period of Cattle Egret at the Ouajaa Marsh lasted from 12th April to 20th July 2014. Egg morphometrics were similar between central and peripheral nests. Overall, Cattle Egret’s eggs measured 46.18 ± 2.03mm. Clutch size was on average 3.43 ± 0.91 eggs (N=53 nests). Overall, hatched eggs averaged 2.72 ± 0.91 per nest, whereas the number of fledglings totaled 134 chicks with an average 2.53 ± 0.85 per nest. The reproductive success at Guerbes-Sanhadja wetlands was 73.6%. However, it was higher (84%) in three-egg nests. GLMs showed that the number of hatchlings increased significantly with the increase of clutch size (P = 0.032), and it was significantly higher (P = 0.028) in central nests (2.74 ± 0.96 chicks) compared to peripheral nests (2.68 ± 0.82 chicks). GLM revealed that the number of hatchlings positively influenced the variation of the number of fledglings (P<0.001), while the effects of nest site characteristics, nest traits and clutch size were not significant. Our findings indicate that cattle egrets prefer relatively shorter nesting heights above the water surface, which reflects that colonies built above water have more secure aspects compared to inland nesting sites. Consequently, vegetation structure is an important criterion for the choice of a specific nesting site among ardeids. © 2019 Elsevier B.V. All rights reserved.

1. Introduction ∗ Corresponding author at: Department of Natural and Life Sciences, Faculty of Sciences, University of 20th August 1955, Skikda 21000, Algeria. ∗∗ Corresponding author at: Department of Natural and Life Sciences, Faculty of Exact Sciences and Natural and Life Sciences, University of Tebessa, Tebessa 12002, Algeria. E-mail addresses: [email protected] (S. Metallaoui), [email protected] (H. Dziri), [email protected] (A. Bousseheba), [email protected] (S. Heddam), [email protected] (H. Chenchouni). https://doi.org/10.1016/j.rsma.2019.100979 2352-4855/© 2019 Elsevier B.V. All rights reserved.

Ecological studies on herons have thrived in recent years because these species are good indicators of anthropogenic disturbances in wetland ecosystems (Kour and Sahi, 2013; Massa et al., 2014). Among ardeids, the Cattle Egret (Bubulcus ibis) extended its distributional and breeding ranges from Africa to Europe, Asia, America and Australasia (Maddock and Geering, 1993; Parejo et al., 2001; Setbel, 2008). The phenomenon of Cattle

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S. Metallaoui, H. Dziri, A. Bousseheba et al. / Regional Studies in Marine Science 33 (2020) 100979

Egret invasion is global. Indeed, new populations were established and the species colonized all continents including many oceanic islands, except Antarctica (Siegfried, 1978; Parkes, 2010). During the last two centuries, this Indo-African species spread over Oceania, North and southern Africa, and south-western of Europe (Franchimont, 1986). Nowadays Cattle Egrets are recorded in all countries in South America. Besides, successful broods are noted in most countries in Central America and Mexico (Massa et al., 2014). The global expansion of the Cattle Egret mainly resulted from extrinsic factors related to changes in environmental conditions. However, intrinsic factors linked to species’ biology also played a role in this expansion; mainly its ability to survive under changing environmental conditions and adapt its behavior to cope with the new environmental conditions (Kushlan and Hafner, 2000; Kopij, 2008; Setbel, 2008). The high breeding success contributed too in the spread of the species into new regions where it was become as migrant, but now become resident-breeder. During colony installation, Cattle Egrets select safe nesting sites surrounded by waters (Arendt and Arendt, 1988; Kushlan and Hafner, 2000; Kushlan and Hancock, 2005). The water surrounding nesting site and/or tall nesting trees reduces nest visibility and thus nest predation by potential terrestrial predators (Hilaluddin et al., 2006). Some new inland colonies are established on other habitats than wetlands (Sbiki et al., 2015). Several factors cause population fluctuations. According to Butler (1994), there is little unequivocal evidence that densitydependent factors regulate most wading bird populations. Intraspecific competition for breeding sites, colony-sites, and food supplies appears to be less important in determining the reproductive success or survival in most wading bird species compared to envirnemental variables and characteristics of nesting site. Moreover, it is unclear whether food limits the number of breeding pairs through density-dependent processes. Unpredictable factors such as cold weather events, high winds, human disturbances, diseases, and food shortage can explain reduced breeding success and increased mortality in wading birds in some regions (Butler, 1994; Kopij, 2016; Chenchouni, 2017a). In the Mediterranean Basin, in particular the Western regions, population sizes of the Cattle Egret are increasing since 1980 (Kushlan and Hafner, 2000). While, the most important colonies are registered in Spain and Portugal, North African populations are counted among the most concerned regions (Kushlan and Hancock, 2005). In Algeria until the 19th century, the Cattle Egret has been only breeding in the lakes of Fetzara and Halloula (extreme North-Eastern of the country) and maybe elsewhere in the Tell region (Heim de Balsac and Mayaud, 1962). More recently, the species become abundant breeder in several regions, particularly in north and northeast coastal areas and the High Plateaux region (Isenmann and Moali, 2000; Boukhemza et al., 2000; Samraoui et al., 2007; Setbel, 2008; Sbiki et al., 2015). Herons are an important component of the Guerbes-Sanhadja wetlands (Skikda, Algeria) as they are good indicator species and because of the conservation value they offer to the habitat (Metallaoui, 2010; Metallaoui et al., 2013). Cattle Egrets usually breed in mixed colonies (Kopij, 1997; Sbiki et al., 2015), where competition with other herons may be important (Burger, 1978; Toloa et al., 2017). Amongst the five species of Herons commonly distributed in Algeria, Cattle Egret seems to be the most adaptive one, probably due to its large feeding niche and nonspecificity for the nesting environment. However, the reasons behind the spatiotemporal variations of its breeding success are often unexplained and will remain so until sufficient data on breeding requirements of various nesting habitats are available from different breeding grounds across its distributional range.

Ecologically, wading birds are dependent on wetlands; they use wet and mesic habitats for foraging, nesting, resting, migration stop-over, etc. (Kushlan and Hafner, 2000; Bezzalla et al., 2019). Most wading bird species mainly rely on wetland habitats for feeding, although Cattle Egrets feed mainly on terrestrial prey (Kushlan and Hancock, 2005; Setbel, 2008). Herons usually chose new nest sites and new mates each year. The colony may therefore serve as an assembly site for mate finding (Shirai, 2013). Studies on nesting ecology are of paramount importance in designing conservation plans for maintenance and regulation of bird populations. A good nesting site generally provides protection against predators, adequate stability and materials to support and construct the nest, and also it influences hatching success (Kazantzidis et al., 1997; Shah and Shawl, 2003) and thus fledging success (Shah and Shawl, 2003; Ashoori and Barati, 2013). The Cattle Egret nested for the first time at Guerbes-Sanhadja wetlands in the Ouajaa marsh in 2014 where the total population size was about 750 pairs at the start of its establishment (personal observation, unpublished). The Ouajaa marsh heronry was discovered in 2013 where it used the trees of Ouaja marsh for roosting (no sign of nesting nor breeding). However, according to the local residents and farmers, Cattle Egrets first settled down a dormitory site in 2012, then this dormitory was transformed in 2014 into a breeding site. We presume that the regular and repeated uses of this site occurred since 2012, first as dormitory and roosting site, but the wetland was successfully used for breeding in 2014 as a familiarization and adaptive process to local conditions. Nesting sites with good quality offer protection against predators, strong support to construct the nest, and easy access to feeding sites within near foraging areas. Since we are dealing with a newly established colony of the Cattle Egret, this research aimsed at exploring and describing the first information related to its reproductive ecology in the region. The study investigated the environmental variables involved in nest site selection (e.g. nesting tree species, nesting height, nest placement and nest sizes) and their effects on breeding parameters (i.e. hatching, fledgling and reproductive success). The study tests also the interrelationships between the breeding parameters in combination with nest site variables. 2. Materials and methods 2.1. Study area This study was carried out in Ouajaa marsh (latitude: 36◦ 53′ 19.2′′ N, longitude: 7◦ 18′ 56.3′′ E, surface: 10 ha) located in the Guerbes-Sanhadja wetlands (northern Algeria; Fig. 1). Important internationally, the Ouajaa marsh is considered as an Important Bird Area ‘IBA’ (IBA code: DZ009) and Ramsar site since February 2001 (Ramsar ID: 1056, Wetlands International ID: 1DZ008). The marsh maximum depth is about 2 m in some places. Water of the marsh is used for irrigating fields of the adjacent farmlands. Water level rises during winter that coincides with heavy rains, and decreases progressively during hot summer. Accordingly, the Salix alba and Acacia cyanophylla woods within the marsh are flooded in winter and drained progressively during summer to reach up a waterless-state in late August. The reason behind studying this area is the particular characteristic of the heronry, as it is newly established in the region and because nesting trees are surrounded with water. Out of the ten trees planted in line, four were used by Cattle Egrets for nesting. The nesting trees include Salix alba Linnaeus (Salicaceae) and Acacia cyanophylla Lindley (syn. Acacia saligna) (Fabaceae). The Guerbes-Sanhadja Plain is located within the Mediterranean subhumid bioclimatic zone with two variants: hot subhumid with 96.5% of the total area and mild subhumid for the

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Fig. 1. Location map of the study area ‘Ouajaa marsh’ belonging to the Guerbes-Sanhadja wetlands in the province of Skikda, northern Algeria.

remaining area (Metallaoui, 2010). De Martonne index indicated a value 34 (class = humid climate). The Budyko radiation index of dryness was 1.376 with an aridity index (ratio annual precipitation/annual PET) equals to 0.92 and Gorczynski continentality index is 16.1. Based on long-term meteorological data, January and February were the coldest months with a minimum average temperature of 7 ± 4 ◦ C and August was the warmest month, with a maximum average temperature of 28.7 ± 3 ◦ C and. Whereas December was the wettest month with 181 ± 45.3 mm of precepitation. In contrast, July was the driest month with an average precipitation of 5 ± 1.9 mm. The total rainfall averaged about 796.84 mm per year (Table 1). The Cattle Egret heronry recorded at Ouajaa marsh was exclusively a monospecific colony. At the end of the breeding season, the pond was completely dry, which allowed us to estimate the area occupied by the colony to about 350 m2 . Out of the ten trees planted only four were selected by Cattle Egrets for nesting, and these were near each other. The materials used for nest building composed entirely of dry and unbarked twigs. Following the horizontal nest placement within the crown of the nesting trees (Salix alba and Acacia cyanophylla), nests were classified as central or peripheral. Nest position was defined as ‘peripheral’ when a nest was built at the edge of the colony i.e. at peripheral branches of the nesting tree crown, otherwise a nest was considered as ‘central’ if its position is within tree crown near the trunk (Sbiki et al., 2015). 2.2. Data collection and analysis The monitoring of Cattle Egret nests inside the waterbody of Ouajaa marsh was carried out using a small boat during the breeding season of 2014. Until the end of March, no built nest was observed. The effective monitoring of the colony started at

the first week of April when the first nests were found. Thereafter, periodic surveys (i.e. twice a week) were undertaken from approximately the mid of April to July, which represents the bulk breeding season of birds in this region. The counting of breeding pairs was conducted using 10 × 50 binoculars. Out of 230 active nests of the Cattle Egret, a set of 53 nests in the colony was selected and surveyed in this study. These nests were selected based on their low nesting height (0.7 − 2.75 m) above water surface within trees, whereas the other nests were excluded because they were inaccessible. The chosen nests were labeled with numbers, plotted on a map and their contents were checked every 3–4 days during the entire survey. For each nest, the following parameters were recorded: (i) nest horizontal placement with the crown tree, (ii) nesting height above water level, (iii) nest outer diameter, (iv) nest inner diameter, (v) nest surface area (NSA) was calculated as NSA = π × (D2 /4): with π = 3.1428 and D is the average of the outer and inner nest diameters. These four later parameters were measured as a proxy of the nest construction strength and the volume of nest cup which reflects the vital space for eggs and nestlings that ultimately may constrain clutch size. Morphometric measurements of eggs were taken to 0.1 mm precision using a digital caliper. Egg length (EL) and breadth (EB) were measured at highest points of the egg. Egg volume (EV) and egg shape index (SI) were calculated using the formulas: EV = 0.000509 × EL × EB2 (Hoyt, 1979) and SI = EB/EL × 100 (Panda, 1996). Moreover, we recorded for each active nest: the number of eggs (i.e. clutch size), hatchlings and surviving fledglings at approximately 10 days old because most of chicks are nidifugous and too mobile after this age. Hatching dates were used to retro-estimate the sequence of egg-laying. In our study, egg incubation period ranged between 25 and 26 days. Nesting success (NS) was calculated as: NS = HPm/(HPm + HPo) × 100, where

January

12.8 ± 3.0 13.8 ± 2.8 7.0 ± 4.4 176 ± 47 37.2 ± 9.6 10.3 ± 1.7 6.1 ± 2.2 34 ± 6.9 09:54 03:21 4 126 72 20 1

Parameters

Mean temperature [◦ C] Maximum temperature [◦ C] Minimum temperature [◦ C] Precipitation [mm] Potential evapotranspiration [mm] Water vapor pressure [hPa] Wind speed [km/h] Sunshine frequency [%] Day length [h] Sunshine hours [h] Ground frost frequency [%] Effective rain [mm] Effective rain ratio [%] Number of rainy days Solid precipitation ratio [%] 13.1 ± 2.7 14.3 ± 2.1 7.0 ± 4.3 123 ± 31.2 48.4 ± 7.2 9.6 ± 2.0 6.1 ± 2.4 44 ± 10.2 10:47 04:44 4 99 80 15 1

February 14.8 ± 2.2 17.1 ± 1.6 8.8 ± 4.0 79 ± 19.9 68.5 ± 9.8 11.3 ± 2.1 7.9 ± 1.8 53 ± 8.6 11:55 06:19 1 69 87 11 1

March 15.6 ± 2.0 18.7 ± 1.1 10.0 ± 3.6 53 ± 15.1 84.8 ± 15.1 12.9 ± 3.1 5.8 ± 2.3 52 ± 6.1 13:05 06:48 0 49 92 8 1

April 18.7 ± 1.5 21.6 ± 2.1 13.1 ± 3.0 41 ± 13.1 112.5 ± 8 15.6 ± 3.4 5.8 ± 2.0 62 ± 6.9 14:05 08:43 0 38 93 6 0

May 22.1 ± 1.8 25.0 ± 2.5 16.6 ± 2.7 18 ± 6.5 131.9 ± 8.2 16.8 ± 4.8 5.8 ± 2.4 66 ± 6.8 14:35 09:37 0 17 97 2 0

June 25.0 ± 1.9 28.2 ± 3.6 19.2 ± 2.4 5 ± 1.9 155.5 ± 12.7 22.2 ± 5.6 5.8 ± 1.4 78 ± 8.5 14:21 11:11 0 5 99 1 0

July 25.7 ± 2.0 28.7 ± 3.0 20.5 ± 2.6 8 ± 3.7 145.2 ± 10.1 23.6 ± 6.3 6.1 ± 1.4 76 ± 6.2 13:30 10:15 0 8 99 1 0

August 24.6 ± 2.3 26.6 ± 1.8 18.7 ± 3.5 42 ± 10.4 109.5 ± 7.0 20.8 ± 5.4 6.1 ± 1.2 70 ± 8.4 12:23 08:40 0 39 93 5 0

September

21.3 ± 2.6 22.7 ± 2.1 15.0 ± 4.5 106 ± 25.8 71.0 ± 8.3 17.5 ± 3.6 5.8 ± 1.5 54 ± 6.1 11:12 06:03 0 88 83 12 0

October

17.2 ± 3.0 18.2 ± 2.5 11.6 ± 4.7 135 ± 27.4 49.1 ± 7.4 13.3 ± 2.1 6.1 ± 1.6 41 ± 8.5 10:10 04:10 0 106 78 16 0

November

14.1 ± 3.1 15.0 ± 3.2 8.8 ± 4.8 181 ± 45.3 37.4 ± 8 11.2 ± 1.9 7.2 ± 1.7 36 ± 8.9 09:37 03:27 1 129 71 20 1

December

18.8 ± 2.3 20.8 ± 2.4 13.0 ± 3.7 80.6 ± 20.6 87.6 ± 9.3 15.4 ± 3.5 6.2 ± 1.8 55.5 ± 7.7 12:08 06:57 1 Σ = 773 80 Σ = 117 1

Mean/Σ

Table 1 Long-term monthly climatic data of Ouajaa Marsh belonging to the Guerbes-Sanhadja wetlands in the province of Skikda, northern Algeria. (latitude: 36◦ 53′ 19.2′′ N, longitude: 7◦ 18′ 56.3′′ E, altitude: 20 m a.s.l.)

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S. Metallaoui, H. Dziri, A. Bousseheba et al. / Regional Studies in Marine Science 33 (2020) 100979

HPm = number of successful nests (i.e. nests bearing at least one nestling survived beyond 15 days of age); HPo = number of unsuccessful nests (i.e. nests with no eggs hatched). Hatching success was calculated as the number of eggs hatched/clutch size × 100 (Fazili, 2002). Fledging success = (fledglings/hatchlings) × 100, represent the ratio between the number of chicks successfully fledged and the number of hatchlings (Parejo et al., 2001). Breeding success was calculated as: number of fledglings survived/clutch size × 100 (Jehle et al., 2004). During all the study period, no evidence of predation activity on the sampled nests was observed. However, 5.5% of chick lost was estimated based on dead bodies found hung on branches probably due chick’s high mobility within branches of the nesting trees or antagonism between conspecifics. A total of ten dead hatchlings were observed on tree branches outside nests. Losses were generally more important after hutching than during chick rearing stage. 2.3. Statistical analysis The data collected from each nest were used in statistical analyses. Data were summarized as means ± standard deviations for nest positions and nesting tree species. The variation of nest morphometric parameters (nesting height, outer and inner diameters and nest surface) were tested using two-way ANOVA with ‘nest positions’, ‘nesting tree species’ and their interaction taken as explanatory variables. The interrelationships between egg traits (egg length, breadth, volume) were tested using a generalized linear mixed-effects models (GLMM), with the nest ID as random effect and egg dimensions in interaction with nest placement and nesting tree species as fixed effects. The variation of breeding parameters (i.e. clutch size, number of hatchlings and fledglings) were analyzed using generalized linear models (GLM) followed by type-III likelihood ratio (LR) tests (McCulloch et al., 2008). For each GLM, all nest site parameters viz. nest placements (with two variants: central or peripheral), nesting tree species, nesting height, and nest surface (a proxy of nest outer and inner diameters) were included as explanatory variables. In addition, the interactions between nest placements, nesting tree species and nest dimensions were considered in the initial full model, that included also clutch size for modeling hatchlings, and clutch size and the number of hatchlings for modeling the variation of fledgling numbers. The ‘backward/forward’ stepwise selection procedure was used to simplify each model based on Akaike information criterion (AIC). The final model was selected as the one with the lowest AIC value. Statistical tests were performed using the software R (R Core Team, 2018). 3. Results 3.1. Breeding chronology In Ouajaa marsh, no nest of Cattle Egrets was observed during and before late March although about 1500 individuals were counted during all day-roosts at the same site. This gathering at the beginning of bird breeding season announced probable pair formation and then nest construction. The breeding period of Cattle Egret at the study area lasted from 12th April to 20th July 2014. The first nests were found during the second week of April, which revealed that nest building started in the beginning of April. Egg hatching was asynchronous as it began the last week of April and lasted till the last week of June. At the end of July, the colony was totally abandoned by parents and all fledglings. It is noteworthy mentioning that in late June, eight new nests were newly built on the same trees of the colony. Already, these late nests were at the egg-incubation phase. We

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suggest that some Cattle Egret pairs have a second brood during the same breeding season or maybe these broods were some late replacement clutches. These broods were not monitored due to the high height of nest placement (height above water surface >3 m) within trees. 3.2. Location and dimensions of nests The average nesting height above water surface was 1.51 ± 0.5 m (range: 0.70 − 2.75 m). Nests of Salix alba (n = 23) were at 1.62 ± 0.6 m above water surface, whereas nesting height in Acacia cyanophylla (n = 30) averaged 1.42 ± 0.4 m. Central nests (n = 34) were at 1.49 ± 0.46 m above water, while peripheral nests (n = 19) were built on average at 1.53 ± 0.57 m above water surface. The ANOVA showed no significant difference in nesting height between nest placements, nesting tree species and their interaction. Nest outer and inner diameters averaged 24.0 ± 3.5 cm and 13.7 ± 2.6 cm, respectively, in central nests, whereas in peripheral nests they were 25.3 ± 3.1 cm and 13.6 ± 2.2 cm, respectively. The inner diameter of A. cyanophylla nests (15.08 ± 2.14 cm) was significantly smaller than S. alba nests (12.64 ± 2.17 cm). The average nest surface was 4.87 ± 1.30 dm2 , with 4.6 ± 1.4 dm2 in central nests and 5.1 ± 1.2 dm2 in peripherals (Fig. 2). Except the significant variation of nest inner diameter between nesting tree species (ANOVA: F(1,23) = 7.41, P = 0.012), nest diameters and surface showed no significant difference between nest placements, nesting trees and their interaction ‘Placement × Tree’. 3.3. Egg characteristics Overall, Cattle Egret’s eggs measured 46.18 ± 2.03 mm (range: 42–51) in length, 34.22 ± 1.02 mm (range: 31–37) in breadth, with 27.55 ± 1.99 cm3 (range: 20.54 − 31.80) of volume and 74.24 ± 3.88 (range: 65.31 − 82.22) for shape index. In A. cyanophylla nests, egg length, breadth and volume averaged 46.81 ± 2.25 mm, 34.22 ± 0.85 mm and 27.92 ± 1.93 cm3 , respectively; whereas egg traits of S. alba nests were 45.43 ± 1.44 mm, 34.22 ± 1.2 mm, and 27.11 ± 2.02 cm3 for length, breadth and volume, respectively. Egg morphometrics were very similar between central and peripheral nests (Table 2). Egg volume increased significantly with the increase of egg length (GLMM: t = 52.35, P < 0.001), breadth (GLMM: t = 77.76, P < 0.001). GLMM showed a higher increase of volume with the increase of egg breadth in peripheral nests (GLMM: t = 2.69, P = 0.012) compared to centrals (Fig. 3). The GLMMs revealed that eggs of peripheral nests built on S. alba have higher volume (GLMM: t = 3.99, P = 0.003) but significantly lowed length and breadth (P < 0.05) compared to central nests constructed on A. cyanophylla (Table 3). The GLMMs indicated that there is a significant positive relationship between egg length and breadth for peripheral nests built on S. alba. However, they showed no significant difference in egg length and breadth between central and peripheral nests (Fig. 3, Table 3). 3.4. Distribution of breeding parameters over clutch sizes The common clutch size in Cattle Egrets breeding at Ouajaa marsh in 2014 (n = 53 nest) was 3–4 eggs, 3 being the most common (27 nests) and exceptionally 5 and 7 eggs. The mean of overall clutch size was 3.43 ± 0.91 eggs (range: 2–7 eggs), 3.21 ± 0.73 in central (total of clutch sizes = 63 eggs in nests with 3 eggs) and 3.84 ± 1.07 in peripheral nests (sum of clutch sizes = 36 eggs in nests with 4 eggs). The common clutches of three and four eggs have higher hatching success compared to other clutches (Table 4). Reproductive success was highest in

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S. Metallaoui, H. Dziri, A. Bousseheba et al. / Regional Studies in Marine Science 33 (2020) 100979

Fig. 2. Violin plots with overlaid boxplots representing the variation of nest measurements (nesting height above water surface, nest outer and inner diameters, and nest surface) of the Cattle Egret for nest placements and nesting tree species in the Guerbes-Sanhadja wetlands at northern Algeria. The solid white circles are markers of the means.

Table 2 Egg characteristics of the Cattle Egret breeding at Guerbes-Sanhadja wetlands in Algeria. Data presented are mean ± standard deviation (Mean ± SD), interquartile range (IQR) and range [min–max] in square brackets. Egg characteristics

Statistics

Nest placement

Nesting tree species

Central (n = 26)

Peripheral (n = 24)

Acacia cyanophylla (n = 27)

Salix alba (n = 23)

Overall (n = 50)

Length [mm]

Mean ± SD IQR Range

46.23 ± 1.63 2.0 [44–49]

46.13 ± 2.42 4.3 [42–51]

46.81 ± 2.25 4.0 [43–51]

45.43 ± 1.44 1.0 [42–49]

46.18 ± 2.03 3.0 [42–51]

Breadth [mm]

Mean ± SD IQR Range

34.42 ± 1.06 1.0 [32–37]

34.00 ± 0.93 0.3 [31–35]

34.22 ± 0.85 1.0 [32–35]

34.22 ± 1.20 1.0 [31–37]

34.22 ± 1.02 1.0 [31–37]

Shape index [%]

Mean ± SD IQR Range

74.57 ± 3.93 6.3 [67.35–82.22]

73.88 ± 3.88 5.5 [65.31–81.40]

73.27 ± 3.99 6.4 [65.31–81.40]

75.38 ± 3.48 3.9 [67.35–82.22]

74.24 ± 3.88 5.8 [65.31–82.22]

Volume [cm3 ]

Mean ± SD IQR Range

27.89 ± 1.71 1.7 [23.98–31.36]

27.17 ± 2.23 2.9 [20.54–31.80]

27.92 ± 1.93 2.4 [23.98–31.80]

27.11 ± 2.02 1.6 [20.54–31.36]

27.55 ± 1.99 2.3 [20.54–31.80]

the three-egg clutches, but lower in clutches with seven eggs. Fledging success was higher in the nest of seven eggs than in the common clutches (Table 4). Overall, hatched eggs averaged 2.72 ± 0.91 per nest (range: 1–5 hatchlings) (Fig. 4). In central nests, it totaled 56 hatchlings, with 45 hatchlings recorded in Acacia cyanophylla nests that have 3-egg clutch. Overall, the number of fledglings totaled 134 chicks with an average 2.53 ± 0.85 per nest (Fig. 4), the highest value (53 chicks) was recorded in

central nests with 3-egg clutch (Table 4). The highest values of hatching success were recorded in two-egg clutches in peripheral nests (100%) followed by three-egg clutches (∼90%), and four-egg clutches in central nests (80%). Nests with two eggs, and five-egg peripheral nests and those built on Salix alba have the maximum fledging success (100%). The overall fledging success in nests with 7 eggs was 93.1%. The reproductive success in general was 73.6%.

S. Metallaoui, H. Dziri, A. Bousseheba et al. / Regional Studies in Marine Science 33 (2020) 100979

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Fig. 3. Scatterplots displaying relationships between egg dimensions (length, breadth and volume) in the Cattle Egrets breeding at Guerbes-Sanhadja wetlands in northern Algeria. Values are set to egg volume and the shape of points representing nesting tree species and the color mapped to nest placement within trees. The solid lines represent linear regressions obtained by a Gaussian GLM fit with confidence regions in light gray.

However, in nests with three eggs it was 84% and 76.6% in nest with four eggs (Table 4). 3.5. Effects of nest characteristics on clutch size Table 5 includes results of the models testing the effects of nest site and nest characteristics combined with some breeding parameters on the variation on reproduction of the Cattle Egret. According to the GLM testing the variation of clutch size, the predictive variables related to nest site characteristics (i.e. nest placements and nesting tree species) and nest traits (i.e. nesting height and nest surface) have no significant effects (P > 0.05). Indeed, nest traits seems to have no effect on the variation of number of eggs per nest regardless of nest horizontal position within trees or the nesting tree species (Table 5, Fig. 5).

and central placements (χ 2 = 4.85, P = 0.028), where hatchling numbers in central clutches (2.74 ± 0.96 chicks) were greater than those of peripheral clutches (2.68 ± 0.82 chicks). The model revealed that the effect of clutch size on the variation of the number of hatchlings differed following nest peripheral/central placements (χ 2 = 4.16, P = 0.041) (Table 5). In fact, the number of hatchlings increased significantly with the increase of clutch size in central nests compared to peripheral nests (Fig. 6). Regardless of nest placements, the GLM indicated no significant effects (P > 0.05) of nesting height and nest surface on the variation of hatched eggs. Although the number of hatchlings seemed to be positively associated with nests built on S. alba (mainly in combination with clutch size: Fig. 6), as it yielded

3.6. Variation of the number of hatchlings The GLM showed that number of hatchlings increased significantly with the increase of clutch size (LR: χ 2 = 4.58, P = 0.032). The number of hatchlings varied significantly between peripheral

higher scores in central nests (2.67 ± 0.84 hatchlings) compared to peripherals (2.78 ± 1.0 hatchlings), the GLM demonstrated that the nesting tree species and its interactions with nest traits have no significant effects (Table 5, Fig. 6).

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Table 3 Parameters of the generalized linear mixed-effects models (GLMM, with Gaussian distribution) testing the relationships between egg traits (egg length ’EL’, egg breadth ’EB’, egg volume ’EV’) for different nest placements (central vs. peripheral) and nesting tree species (Acacia cyanophylla vs. Salix alba) of the Cattle Egret breeding at Guerbes-Sanhadja wetlands in northern Algeria. Gaussian GLMM (Egg volume ∼((egg length + egg breadth) × nest emplacements × nesting trees)) Variables

Value

Intercept Egg length Egg breadth Peripheral nests Salix alba Peripheral nests × Salix alba Egg length × Peripheral nests Egg length × Salix alba Egg breadth × Peripheral nests Egg breadth × Salix alba Egg length × Peripheral nests × Salix alba Egg breadth × Peripheral nests × Salix alba

−54.91 0.61 1.58 −2.21 0.19 8.26 −0.01 −0.03 0.08 0.04 −0.01 −0.23

Std. Error 0.872 0.012 0.020 1.248 1.677 2.069 0.014 0.022 0.031 0.029 0.031 0.044

DF

t-value

P

29 29 29 9 9 9 29 29 29 29 29 29

−62.97

<0.001* <0.001* <0.001*

52.35 77.76 −1.77 0.12 3.99 −1.00 −1.40 2.69 1.23 −0.24 −5.24

0.111 0.910 0.003* 0.325 0.171 0.012* 0.227 0.816 <0.001*

Gaussian GLMM (Egg length ∼(egg breadth × nest emplacements × nesting tree species)) Variables

Value

Std. Error

DF

t-value

Intercept Egg breadth Peripheral nests Salix alba Peripheral nests × Salix alba Egg breadth × Peripheral nests Egg breadth × Salix alba Egg breadth × Peripheral nests × Salix alba

53.34 −0.20 22.11 19.19 −71.20 −0.64 −0.57 2.04

15.957 0.466 24.465 20.049 31.149 0.715 0.583 0.912

33 33 9 9 9 33 33 33

3.34 −0.43 0.90 0.96 −2.29 −0.89 −0.98 2.24

P 0.002* 0.671 0.390 0.364 0.048* 0.380 0.334 0.032*

Gaussian GLMM (Egg breadth ∼(egg length × nest emplacements × nesting tree species)) Variables

Value

Std. Error

DF

t-value

Intercept Egg length Peripheral nests Salix alba Peripheral nests × Salix alba Egg length × Peripheral nests Egg length × Salix alba Egg length × Peripheral nests × Salix alba

32.37 0.04 2.84 29.52 −50.75 −0.06 −0.64 1.10

6.947 0.149 8.301 11.389 16.057 0.177 0.247 0.352

33 33 9 9 9 33 33 33

4.66 0.27 0.34 2.59 −3.16 −0.35 −2.58 3.12

P

<0.001* 0.787 0.740 0.029* 0.012* 0.727 0.014* 0.004*

SE.: standard error, DF: degrees of freedom, P: P-value. *Significant effects (P ≤0.05) are displayed in boldface font.

3.7. Effects of clutch size, hatching success and nest traits on number of fledglings The simplification of the GLM testing the effects of nest site characteristics, nest traits, clutch size and number of hatchlings on the variation of the number of fledglings resulted a model in which the number of hatchlings was found to be the significant predictor of fledgling variation. Regardless of nest horizontal position within tree crown or the nesting tree species, the selected GLM revealed that the number of fledglings increased significantly with the increase of the number of hatchlings (Table 5, Fig. 7). Although the number of hatched eggs was demonstrated to be positively linked with clutch size, the latter had no significant effect (P = 0.454) on the variation of the number of fledglings. Similarly, number of fledglings showed no significant variation between nest placements and nesting tree species. Likewise, nesting height above water level and nest surface were deemed to have no significant effects on number of fledglings (Table 5, Fig. 7).

Cattle Egret colony in all the Guerbes-Sanhadja wetlands. This monospecific colony includes more than 230 confirmed breeding pairs. The duration of breeding season of the Cattle Egret varies from one region to another. In the Ouajaa marsh it lasts four months from the beginning of April to the end of July. Setbel (2008) reported a breeding period a little longer than four months, from Late-March to Late-July. However, in Camargue (France), the nesting period is shorter but later compared to breeding grounds in North Africa; it begins the second decade of April and lasts until late August (Hafner, 1980). Similarly, the breeding period in the Salton Sea region lasts from April to July (Patankar et al., 2007). Furthermore, the Cattle Egret may raise a second and even a third brood per year; several cases were reported worldwide (Prosper and Hafner, 1996; Setbel, 2008; Dragonetti and Giovacchini, 2009). Besides, the difference in timing and duration of the breeding season between regions depicts that species’ breeding is very closely related to seasonal varia-

4. Discussion In Algeria, the Cattle Egret bred at Halloula and Fetzara wetlands since the nineteenth century (Heim de Balsac and Mayaud, 1962) and it is still breeding in many other regions of the country (Isenmann and Moali, 2000; Setbel, 2008). At the Ouajaa marsh, the study colony is newly established and seems to be the sole

tion of climatic conditions that control food resources in foraging habitats (Weber, 1975; Hafner and Fasola, 1992). Birds have developed evolutionary adaptations that enable them matching their breeding cycle with the favorable climatic season which offers abundant food resources to rise adequately their offsprings (Fazili, 2002; Chenchouni, 2017b).

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Table 4 Breeding parameters of the Cattle Egret nesting at Guerbes-Sanhadja wetlands in northern Algeria. Reproduction data were grouped for each clutch size per nesting trees species (Acacia cyanophylla vs. Salix alba) and nest horizontal positions within trees (Central vs. Peripheral). Parameters

Clutch size

Total

2

3

4

5

7

2 3 4 1 5

17 10 21 6 27

7 9 7 9 16

3 1 2 2 4

1 – – 1 1

30 23 34 19 53

4 6 8 2 10

51 30 63 18 81

28 36 28 36 64

15 5 10 10 20

7 – – 7 7

105 77 109 73 182

3 3 4 2 6

45 27 56 16 72

22 31 25 28 53

8 3 8 3 11

2 – – 2 2

80 64 93 51 144

3 3 4 2 6

43 25 53 15 68

20 29 23 26 49

7 3 7 3 10

1 – – 1 1

74 60 87 47 134

75.0 50.0 50.0 100 60.0

88.2 90.0 88.9 88.9 88.9

78.6 86.1 89.3 77.8 82.8

53.3 60.0 80.0 30.0 55.0

28.6 – – 28.6 28.6

76.2 83.1 85.3 69.9 79.1

100 100 100 100 100

95.6 92.6 94.6 93.8 94.4

90.9 93.5 92.0 92.9 92.5

87.5 100 87.5 100 90.9

50.0 – – 50.0 50.0

92.5 93.8 93.5 92.2 93.1

75.0 50.0 50.0 100 60.0

84.3 83.3 84.1 83.3 84.0

71.4 80.6 82.1 72.2 76.6

46.7 60.0 70.0 30.0 50.0

14.3 – – 14.3 14.3

70.5 77.9 79.8 64.4 73.6

Number of nests A. cyanophylla Salix alba Central Peripheral Overall

Sum of clutch sizes [eggs] A. cyanophylla Salix alba Central Peripheral Overall Number of hatchlings A. cyanophylla Salix alba Central Peripheral Overall Number of fledglings A. cyanophylla Salix alba Central Peripheral Overall Hatching success [%] A. cyanophylla Salix alba Central Peripheral Overall Fledging success [%] A. cyanophylla Salix alba Central Peripheral Overall Breeding success [%] A. cyanophylla Salix alba Central Peripheral Overall

The expansion of breeding range of the Cattle Egret in several regions of the world is especially explained by its capacities of adaptation to new environments. Several studies argue that Cattle Egret’s geographical expansion worldwide is not only favored by intrinsic factors related to species characteristic (large clutch size, several broods per year, high breeding success, short incubation period, early sexual maturity, and broad trophic niche); but the colonization process of new regions also includes factors connected to environmental conditions and human activities such as expansion of croplands to the detriment of forest, agriculture intensification, and the development of animal farming and new irrigated areas (Hafner and Fasola, 1992; Kushlan and Hafner, 2000; Setbel, 2008; Parkes et al., 2012). Colonial nesting herons have been shown to differentially partition nest site resources on a spatial and temporal basis in mixed-species colonies (Hafner, 1980; Telfair and Bister, 2004; Ashoori and Barati, 2013). Nesting height is an essential driver of

breeding success in temporal marshes, because it confers more protection against terrestrial predators (Shah and Shawl, 2003; Ashoori and Barati, 2013). The selection of suitable nest site location viz. nesting height and location within vegetation is thought to increase reproductive success by reducing interspecific competition in mixed species colonies (Burger, 1978; Ashoori and Barati, 2013; Toloa et al., 2017) and reducing the odds of being predated (Chenchouni, 2017a). In addition to competition for nest location, Burger (1978) reported that competition for nest materials occurred through the pre-egg-laying and incubation periods. Usually nest material was stolen while nests were unattended. On the one hand, Cattle Egrets showed the highest aggression rates as it removed material from nests being defended by other species (Burger, 1978); which indicates high inter- and intra-competitions for suitable nest placement.

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Table 5 Generalized linear models testing the effects of: nest site and nest characteristics on the variation of clutch size (GLM1), nest characteristics and clutch size on number of hatchlings (GLM2), and nest characteristics, clutch size and number of hatchlings on the variation of number of fledglings (GLM3) of Cattle Egrets breeding at Guerbes-Sanhadja wetlands in Algeria. Model parameters were selected using the ‘backward/forward’ stepwise procedure based on the lowest AIC. Variables

LR χ 2

P

Sig.

0.554 0.328 0.078 0.114 0.172

0.457 0.567 0.781 0.735 0.679

NS

4.577 4.851 0.108 1.846 0.392 0.626 4.159 0.023 1.874 0.687

0.032 0.028 0.742 0.174 0.531 0.429 0.041 0.881 0.171 0.407

31.609 0.560 0.140 0.751 0.349 0.399 0.978

<0.001 0.454 0.708 0.386 0.555 0.528 0.323

GLM1: Clutch size (AIC = 97.51, ∆AIC = 7.84) Nest placement Nesting tree species ‘Tree’ Nesting height Nest surface Tree × Nesting height

NS NS NS NS

GLM2: Number of hatchlings (AIC = 64.76, ∆AIC = 2.00) Clutch size Nest placement ‘Placement’ Nesting tree species ‘Tree’ Nesting height Nest surface Placement × Tree Clutch size × Placement Clutch size × Tree Clutch size × Nesting height Clutch size × Placement × Tree

* * NS NS NS NS

* NS NS NS

GLM3: Number of fledglings (AIC = 40.84, ∆AIC = 13.24) Number of hatchlings Clutch size Nest placement Nesting tree species Nesting height Nest surface Clutch size × Nesting tree species

*** NS NS NS NS NS NS

LR χ 2 : chi-square of the likelihood ratio test, P: P-value, AIC = Akaike information criterion of the selected GLM, ∆AIC = AIC difference between the full GLM and the simplified one with the lowest AIC based on ‘backward/forward’ stepwise selection procedure, Sig.: probability significance codes, NS : P > 0.05. *P ≤ 0.05. ***P < 0.001.

Dimensions of Cattle Egret’s nests in the study area are quite similar to those found in the literature. For example, the outer and inner diameters of nests were about 24.8 cm and 13.6 cm, respectively; which are substantially similar to the mean diameter reported in India (Patankar et al., 2007). However, nest diameters of the current study are much larger than the average diameters (17.9 cm) reported at Montserrat in West Indies (Arendt and Arendt, 1988), but on the other hand they are smaller than nest diameters described from North America (31.9 cm) (Telfair, 1983), New Jersey (35.8 cm) (Burger, 1978), and South Africa at Paarl (36.3 cm) (Siegfried, 1971). In a South African heronry, Kopij (1996), reported a mean nest diameter pf 26.3 cm (range: 17–36), and mean nest height 12.3 cm (range: 6–25 cm). Moreover, nesting height data reveal that Cattle Egrets nesting in mixed and monospecific colonies construct their nests at a mean height of about 1.9 m (Arendt and Arendt, 1988), with some exceptions such as the case where nesting height averaged 7.4 m (Hafner, 1980). In Ouajaa marsh, Cattle Egrets nest on average at a height of 1.6 m above water level (range: 0.70 − 2.75 m). These findings suggest a preference of relatively shorter nesting heights in colonies built on water compared to tree nests above ground: as it is the case for an inland colony newly established in Algeria, where the average nesting height was 11.5–13.2 m (Sbiki et al., 2015). These large differences in nesting heights can be explained by the type of the colony, i.e. whether it is established above water or on firm ground. We suggest that colonies built up above water have more secured site features, thus birds opt for a low nesting height, while nests constructed on tree on the ground have a higher placement above the ground. This specific nest site selection is probably a strategy to avoid terrestrial predation and other disturbance sources, mainly anthropogenic, coming from below, which are much lesser or absent when nests are built

above water. Moreover, this nest site selection in colonies established above waters can be considered as a strategy to avoid aerial predators, because predation risk decreases with the decrease of nesting height (Chenchouni, 2017a). The suitability of Ouajaa marsh as a breeding habitat for the Cattle Egret can be explained by the presence of a variety of favorable factors such as: (i) agricultural fields near the colony that represent valuable foraging habitats, specifically during chick rearing, (ii) many grazing herds of sheep and cattle frequent the surrounding sites, (iii) tree vegetation with specific structure and characteristic (trunk diameter, height, crown width, density, solidity of branches, . . . ) that enables setting-up the colony with large carrying capacity. These suitable conditions of the nesting site gave Cattle Egrets protection against predators and offered adequate nest stability and abundant materials to support and construct the nest, and above all easy access to high quality foraging habitats that offer adequate feeding resources that timely match nutritional needs during different phases of the breeding season (Hafner and Fasola, 1992; Chenchouni et al., 2015). The variation of clutch size can originate from phenotypic response to environmental conditions (Murphy, 1983) or genetic variation (Van Noordwiijk et al., 1980). Maximum clutch size of the Cattle Egret was determined to be six eggs (Shah and Shawl, 2003), five eggs (Arendt and Arendt, 1988; Iyer, 2004) and in the range of 2–5 eggs (Weber, 1975; Kopij, 1997, 1999). Our results fit within this pattern. Indeed, the average clutch size recorded is 3.43 eggs per nest, which is similar to that reported by Darmallah (1990) at Bou Redim in El Kala (Algeria) but slightly higher

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Fig. 4. Violin plots with overlaid boxplots representing the distribution of clutch size, hutched eggs and fledged chicks of the Cattle Egret per nest placements and following nesting tree species in the Guerbes-Sanhadja wetlands at northern Algeria. The solid white circles are markers of the means.

than that found by Samraoui et al. (2007). Franchimont (1985) indicated an average clutch size of 3.27 for a colony in Asjène in Morocco, whereas Kopij (1997) reported a value of 3.0 based on 1217 nests in a South African heronry. In South African colonies, the most common clutches contained three eggs, whereas twoand four-egg-clutches were less common while clutches with one and five eggs were only laid occasionally (Kopij, 1997, 1999). It is also within the range of results reported in North Africa that are generally lower compared to southern Europe where

records showed clutch sizes averaged 4.23–4.6 eggs (Prosper and Hafner, 1996). Our results revealed that the common clutch size in Guerbes-Sanhadja wetlands was 3–4 eggs/nest, which is in agreement with the theory of Lack (1954) according to which the most frequent clutches are usually the most successful and therefore of the highest adaptive value. The hatching success during the study period was 79.1% with a mean interval predicted at 2.72 ± 0.91 hatchling per nest which is higher than that of Samraoui et al. (2007).

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Fig. 5. Relationship between clutch size and nest characteristics (nesting height and nest surface) of Cattle Egrets breeding at Guerbes-Sanhadja wetlands in northern Algeria. Observations are grouped by nest horizontal placements (top plots) and by nesting tree species (bottom plots). The solid lines represent linear regressions obtained by Poisson GLM fit with confidence regions in light gray.

Fledging success (73.62%) is not an indicator of the adaptive value of the average clutch size, as it adverts to the hatching success. While it was not affected by vegetation structure of nesting site, which is an important criterion for the choice of a specific nesting placement in Ardeids (Subramanya, 1996; Sbiki et al., 2015). In the studied colony, hatching success and clutch size were positively associated, in particular in central nests, and notably for nests built on Acacia cyanophylla. Sharah and Ali (2012) reported that the preference of Cattle Egret for Acacia trees is justified by some factors such as the very strong and hard wood of Acacia trees, where even the upper-most very thin branches can support nests. In Cattle Egret, the latter have lightweight compared to most other wading Ciconiiform birds. The significant effect of nest placement (central and peripheral) on hatching success was reported in several studies (Siegfried, 1972; Ranglack et al., 1991; Kopij, 1997). Given their location within vegetation (inside tree crown), central nests are safer than peripheral nests as they offer good protection against the effects of the wind and also aerialpredation. Indeed, our findings showed a positive correlation between hatching success and central nests. Although nest site selection affects breeding parameters in several species (Larison et al., 2001; Guezoul et al., 2011; Chenchouni, 2017a), some studies suggest that breeding

success may be independent of nest site (Harris et al., 1997; Kazantzidis et al., 1997). Clutch size in birds is often dependent on the age of the parents, with too younger or too older parents laying smaller number of eggs (Klomp, 1970). In addition, younger breeders are inexperienced and more often have low productivity (Tobolka et al., 2013). The main explanations of the low breeding success in young breeders are related to the occupancy patterns of the nesting site. Bad selection of nest position due to inexperience of parents or unavailability of good sites are common examples. In tree branch nesting birds, the young pairs nesting for the first time generally tend to lay eggs late in the season compared to old birds, thus when central nests are occupied by experienced adults, young breeder are forced to selected peripheral positions (Klomp, 1970), which offer lower quality nesting site. This makes them more vulnerable to adverse meteorological conditions (strong wind, heat, heavy rain, hail, etc.) and predation (Picman et al., 2002; Sharah and Ali, 2008) which leads to significant decrease in chick survival rate and thus lesser breeding success. Safe nesting site, availability of water and food are the

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Fig. 6. Relationship between hatching success and nesting height, nest surface and clutch size of Cattle Egrets breeding at Guerbes-Sanhadja wetlands in northern of Algeria. Observations are grouped by nest placements (top plots) and nesting tree species (bottom plots). The solid lines represent linear regressions obtained by Poisson GLM fit with confidence regions in light gray.

major ecological determinants of Cattle Egret’s nest site selection (Kopij, 2016; Abdullah et al., 2017) and high chick productivity. 5. Conclusion At the Ouajaa marsh, the newly established colony of Cattle Egret was the sole herony in the complex of Guerbes-Sanhadja wetlands. The investigation of breeding ecology of the Cattle Egret was reflective of the overall species ecological success (expansion, breeding, adaptation). Our findings suggest a preference of relatively shorter nesting heights within trees in colonies established above water. This reflects that this kind of monospecific colonies have more secure features of nest site, thus birds opt to lower heights. Vegetation structure is an important criterion for the choice of a specific nesting site among ardeids. The monitoring of the nesting ecology and breeding biology of Cattle Egret throughout the Guerbes-Sanhadja region is suggested in order to further deepen our understanding of nest site selection process. Providing scientists and habitat managers with accurate data on species breeding ecology can contribute to delineate the main factors involved in the spatial expansion of Cattle Egret range and even predict patterns of habitat use, tends of population dynamics and its impacts on ecosystems.

Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

CRediT authorship contribution statement Sophia Metallaoui: Methodology, Data curation, Writing original draft, Writing - review & editing . Hamdi Dziri: Methodology, Data curation . Abderazzak Bousseheba: Data curation. Salim Heddam: Writing - original draft, Writing - review & editing. Haroun Chenchouni: Data curation, Conceptualization, Writing - original draft, Writing - review & editing.

Acknowledgments We sincerely thank the inhabitants of Ben Azzouz (Skikda, Algeria) particularly the families of Ouajaa for their full support, collaboration and hospitality during the realisation of this study. Many thanks extend to the students Khawla Boukhmiss and Nour El Islam Alleg for their assistance in the fieldwork.

Availability of data and materials The datasets used and/or analyzed during the current study are available from the corresponding authors on reasonable request.

Funding This study was not funded by any source.

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Fig. 7. Relationships between the number of fledglings and nesting height, nest surface, clutch size and number of hatchlings of Cattle Egrets breeding at GuerbesSanhadja wetlands in northern of Algeria. Observations are grouped by nest placements and nesting tree species. The solid lines represent linear regressions obtained by Poisson GLM fit with confidence regions in light gray.

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