La production, la taille des oeufs et les conditions corporelles des poussins ont été étudiées chez le Héron garde-boeufs (Bubulcus ibis), l'Aigrette
        intermédiaire (Egretta intermedia), l'Aigrette garzette (Egretta garzetta), le Crabier chinois (Ardeola bacchus) et le Bihoreau gris (Nycticorax nycticorax) en deux sites de Chine centrale et dans quatre autres au Pakistan. La production en Chine s'est avérée très forte, plus importante
        qu'au Pakistan, probablement en relation avec une grande disponibilité de zones humides pour l'alimentation. La forme sombre de l'Aigrette garzette de la côte du Pakistan présentait une productivité significativement plus faible que celle des formes blanches

BONCOMPAGNI, Eleonora

CANOVA, Luca

DONG, Yuanhua

FASOLA, Mauro

MUHAMMAD, Ashiq

NAJAM, Rahat

WEI, Liu

ZHANG, Yingmei

I-Revues

Rev. Écol. (Terre Vie), vol. 62, 2007.
 – 369  –
NOTE BRÈVE
BREEDING PRODUCTIVITY OF EGRETS AND HERONS AT SIX SITES IN ASIA
Mauro FASOLA1,7, Luca CANOVA1, Eleonora BONCOMPAGNI1, Ashiq MUHAMMAD2,
Rahat NAJAM3, Liu WEI4, Yuanhua DONG5 & Yingmei ZHANG6
RÉSUMÉ.  — Productivité des aigrettes et hérons nicheurs en six sites asiatiques. — La production, la 
taille des œufs et les conditions corporelles des poussins ont été étudiées chez le Héron garde-bœufs (Bubul-
cus ibis), l’Aigrette intermédiaire (Egretta intermedia), l’Aigrette garzette (Egretta garzetta), le Crabier 
chinois (Ardeola bacchus) et le Bihoreau gris (Nycticorax nycticorax) en deux sites de Chine centrale et dans 
quatre autres au Pakistan. La production en Chine s’est avérée très forte, plus importante qu’au Pakistan, 
probablement en relation avec une grande disponibilité de zones humides pour l’alimentation. La forme 
sombre de l’Aigrette garzette de la côte du Pakistan présentait une productivité signifi cativement plus faible 
que celle des formes blanches.
Abundant data exist on breeding productivity of several species of Ardeinae for Europe 
and for America (Rubolini & Fasola, in press), whereas scanty information is available for 
continental Asia, where breeding was studied only in Israel (Askenazi & Yom-Tov, 1997) and 
at a few other sites (Longsheng et al., 1994; Lizhi et al., 1998; Hilaluddin, 2003). Almost unk-
nown are the breeding parameters of some species, such as the Chinese Pond Heron Ardeola 
bacchus (no detailed study known to us) and the Intermediate Egret Egretta intermedia (only 
studied by Baxter, 1994 and Maddock & Baxter, 1991 in Australia; and by Morel & Morel, 
1961 in Senegal).
We aim to fi ll this gap by describing the breeding productivity of fi ve Ardeinae, Chinese 
Pond Heron, Intermediate Egret, Cattle Egret (Bubulcus ibis), Little Egret (Egretta garzetta), 
and Black-crowned Night Heron (Nycticorax nycticorax), at two sites in Central China on the 
border of Poyang Lake and of Tai Lake, and at four sites in Pakistan, the inland agricultural 
areas near Multan, near Lahore, and near the Taunsa barrage on the River Indus, and the coastal 
area near Karachi. 
1 Dipartimento Biologia Animale, Università, Piazza Botta 9, I-27100 Pavia, Italy
2 National Agricultural Research Center; Park Rd., Islamabad 45500, Pakistan
3 WWF-Pakistan. 606-607Fortune Center, P.E.C.H.S., Shahra-e-Faisal, Karachi 75400. Pakistan
4 Biological Resources Institute, Jiangxi Academy of Sciences, 330029 Nanchang, P.R. China
5 Institute of Soil Science, Chinese Academy of Sciences, 210008 Nanjing, P.R. China.
6 Department of Biology, Lanzhou University, 730000 Lanzhou, P.R. China
7 Corresponding author. E-mail: fasola@unipv.it
 – 370  –
Still unclear is the species or subspecies status of the Little Egret morphs, the nominate 
garzetta, and the dimorpha, gularis, and schistacea. Some authors identify the dark egrets 
breeding on the Indian Ocean coast as a separate species, the Western Reef Heron (Egretta 
schistacea), while we consider all the white and dark morphs as belonging to a single polymor-
phic species (Hafner et al., 2002), and we designate the dark egrets studied at Karachi as Little 
Egret, dark morph Egretta garzetta schistacea. 
We studied breeding productivity as part of a research on egrets as monitors of envi-
ronmental contamination. The level of persistent contaminants, both organic and inor-
ganic, was found to be low at the areas studied both in China and in Pakistan, and well 
below the levels that may affect egret reproduction (Boncompagni et al., 2003; Sanpera 
et al., 2003; Zhang et al., 2006). China holds very large numbers of several species of 
egrets and herons (Fasola et al., 2004), while in Pakistan the most abundant species is the 
Cattle Egret.
STUDY AREAS
We studied a sample of nests at one colony, usually the largest, at each of the following six areas (Fig.1).
Figure1. — The six study areas in Pakistan and China.
(1) Poyang Lake, Jiangxi Province, the largest freshwater lake (3283 km2), still in a near-natural state, and the most 
important site for waterfowl in China. From 15 May to 10 June 1999, we studied a heronry located in a mixed wood 
near Gongqing (29°13’N, 115°49’E), with 580 nests of Little Egret, 165 of Intermediate Egret, 50 of Great White Egret,
420 of Cattle Egret, 70 of Chinese Pond Heron, and 715 of Black-crowned Night Heron. Breeding of the Black-crowned 
Night Heron was already described for a subset of these nests (Fasola et al., 2001).
 – 371  –
(2) Tai Lake, Jiangsu Province, one of the largest freshwater lakes in China (2425 km2), located in a highly 
productive agricultural area, with rice fi elds over 90% of farmed land. From 20 April to 10 June 2000, we studied a very 
large colony in the Yuantouzhu Park (31°31’N, 120°13’E) near Wuxi. The colony stretched over several hectares within 
a large woodland, and included 30,100 nests of Black-crowned Night Heron, 4,200 of Little Egret, 1,000 of Chinese 
Pond Heron, and 1,100 of Cattle Egret.
(3) Taunsa Barrage, Punjab, a storage reservoir behind a barrage on the River Indus in Pakistan. Adjacent areas 
are cultivated with cotton, sugar cane, wheat, and the barrage is used also for power generation. From 5 May and
15 June 2000, we studied a heronry placed 5 km west of the barrage (30°42’N, 70°50’E), with 26 nests of Little Egret, 
22 of Intermediate Egret, 305 of Cattle Egret, and 15 of Black-crowned Night Heron.
(4) Multan agricultural areas, Punjab Province in Pakistan, with mango orchard, wheat, fodder, cotton and rice. 
From 20 May to 15 June 2002, we studied a colony on acacias along a canal near Sardarpur (30°32’N, 71°45’E), 60 km 
North of Multan and about 1 km from River Indus, with 1500 nests of Cattle Egrets.
(5) Lahore, Punjab in Pakistan, an area from 31°47’ to 32° 33’N and from 73° 42’ to 74°35’E, cultivated mainly with 
rice, wheat and fodder. Three heronries with hundreds of nests of Cattle Egrets, at sites called Rehman, Rajanpur, and 
Chack Bhulian-Nordwal Rd, were studied from 2 June to 19 July 2003. 
(6) Karachi Harbor, Sind Province in Pakistan, an area of tidal creeks, mangroves and intertidal mudfl ats, around 
the harbor of Karachi. From 3 to 30 May 2000, we studied a heronry in the Ghas Bunder lagoon (24°47’N, 67°11’E), 
with 115 nests of Little Egret, all dark morphs, 20 nests of Intermediate Egret, and 10 nests of Indian Pond Heron 
Ardeola grayii.
METHODS
We aimed to sample at least 20 nests per species at the peak of the reproductive period, but scarce species permitted 
only smaller samples. In order to avoid disturbing the breeding birds, we sampled the nests that were relatively accessible 
amid the intricate vegetation of the colonies, and those placed from 3 to 6m above ground. We had no evidence that the 
sample nests were biased for any feature related to their productivity. Nest content was checked at least twice per week 
to ascertain the number of eggs, hatched chicks, and “fl edged” chicks. The chicks cannot be tracked after about 20 days 
old, therefore the number “fl edged” refers to the number surviving at 20 days, a measure commonly employed in heron 
nesting productivity studies, and that approaches the fi nal fl edging productivity, since most mortality occurs during the 
fi rst 20 days (Bennetts et al., 2000). The nests that failed completely were not included in the calculations.
For a sub-sample of nests, we measured egg diameters. When the oldest chick was 20 days old, tarsus length 
and body mass were measured for each chick. Since tarsus length depends mainly on age, except in cases of severe 
malnutrition, while mass is largely infl uenced by the amount of food received, the mass in relation to tarsus length 
reliably indicates chick condition (Jacobs, 1996 ; Fasola, 1998). A “condition index” was calculated for each chick as 
ratio between its mass and its tarsus length.
The differences among sites within each species, were tested using non-parametric Kruskal-Wallis test for non-
continuous variables (i.e. number of eggs, number hatched, and number fl edged), and univariate ANOVA for the other 
data (i.e. egg size, condition index) that were normally distributed. When a signifi cant difference was found among sites, 
Bonferroni post-hoc tests were performed for both normal and non-continuous variables, in order to identify the pairs 
of sites that contributed to the difference.
RESULTS
The breeding productivity (Table I) showed few signifi cant differences among areas within 
a species, in the following cases. In the Cattle Egret, both the number hatched, and the number 
fl edged differed (Kruskal-Wallis, χ22 = 14.3, P = 0.01, and χ22 = 11.9, P = 0.03, respectively) 
and particularly they were lower in Multan than at Taunsa and Poyang. In the Little Egret, all 
the variables differed among areas, (number of eggs: χ32 = 48.3, P = 0.0001; number hatched: 
χ22 = 14.5, P = 0.001; number fl edged: χ32 = 18.9, P = 0.0001). These differences for Little 
Egret were due to a much lower productivity of the dark morph in Karachi than at the two sites 
in China (post-hoc tests). In general, there was a constant tendency for the breeding productiv-
ity to be higher, and similar, at the two Chinese sites, Poyang and Tai, than at the three Pakistani 
sites.
 – 372  –
TABLE I
Egg and nestling production, as number of nests recorded for the fi ve egret and heron species at the six study areas. 
Little Egrets at Karachi belonged to the dark morph. The fi gures that differ signifi cantly (P<.01) from the values for 
the other areas within the same species, are marked by *
Number / nest
1 2 3 4 5 6 7 Mean
Eggs
Cattle Egret Poyang 0 0 4 3 3 0 0 3.90
Multan 0 1 25 44 10 3 0 3.87
Tounsa 0 1 30 26 6 1 0 3.63
Lahore 1 12 55 93 33 5 1 3.82
Intermediate Egret Poyang 0 1 7 6 5 0 0 3.79
Tounsa 0 1 6 1 0 0 0 3.00
Little Egret Poyang 0 1 4 18 33 7 0 4.65
Tai 0 1 6 15 36 25 2 4.99
Tounsa 0 0 3 1 2 0 0 3.83
Karachi 0 3 10 17 3 0 0 * 3.61
Chinese Pond Heron Poyang 0 0 0 1 0 1 0 5.00
Tai 0 0 0 2 3 1 0 4.83
Black-crowned Night Poyang 0 0 9 4 1 0 0 3.43
Heron Tai 0 17 116 94 7 0 1 3.40
Hatched
Cattle Egret Poyang 0 2 2 4 1 0 0 3.44
Multan 7 34 21 4 1 0 0 * 2.37
Tounsa 1 12 14 9 0 0 0 2.86
Lahore 9 20 22 6 0 0 0 2.44
Intermediate Egret Poyang 0 3 8 8 1 0 0 3.35
Tounsa 2 1 2 0 0 0 0 2.00
Little Egret Poyang 0 5 7 22 24 0 0 4.12
Tounsa 0 1 0 0 1 0 0 3.50
Karachi 2 4 6 5 1 0 0 * 2.94
Chinese Pond Heron Poyang 0 0 1 1 0 0 0 3.50
Black-crowned Night 
Heron
Poyang 0 0 12 3 0 0 0 3.20
Fledged
Cattle Egret Poyang 0 2 1 2 1 0 0 3.33
Multan 15 32 17 2 1 0 0 * 2.13
Tounsa 4 11 10 9 0 0 0 2.71
Lahore 11 22 20 6 0 0 0 2.36
Intermediate Egret Poyang 0 5 9 3 1 0 0 3.00
Tounsa 1 1 1 0 0 0 0 2.00
Little Egret Poyang 1 5 13 24 11 0 0 3.72
Tai 0 5 15 13 26 8 1 4.30
Tounsa 0 1 1 0 0 0 0 2.50
Karachi 2 2 5 3 1 0 0 * 2.92
Chinese Pond Heron Poyang 0 0 1 1 0 0 0 3.50
Tai 0 0 1 2 2 0 0 4.20
Black-crowned Night Poyang 0 1 10 1 0 0 0 3.00
Heron Tai 14 41 73 38 2 0 0 2.84
 – 373  –
Egg size (Table II) did not differ among sites within a species. The “condition index” 
of the chicks, that could be compared between sites for the Little Egret only, differed among 
sites (F = 47.2, d.f. 3, 265, P < 0.0001), due only to the dark morph in Karachi, where the 
ratio between mass and tarsus length averaged 5.7, and was higher than at the other three sites, 
where the averages ranged from 4.1 to 4.5.
TABLE II
Length and width of eggs for the fi ve species in the six study areas. Each entry is: mean value (standard deviation, 
minimum-maximum, sample size).
Species Study area Length (mm) Width (mm)
Cattle Egret Tounsa 44.5 (2.4, 40.9-48.8, 10) 34.1 (0.6, 32.9-34.7, 10) 
Lahore 43.6 (1.9, 41.0-50.0, 30) 33.5 (1.3, 32.0-36.0, 30)
Intermediate Egret Poyang 45.9 (0.4, 45.6-46.3, 2) 33.2 (0.5, 32.7-33.7, 2) 
Little Egret Poyang 44.1 (1.8, 38.8-48.6, 38) 32.5 (0.8, 30.9-34.1, 38)
Tai 44.5 (2.0, 40.6-48.1, 13) 32.2 (1.1, 30.0-33.5, 13)
Tounsa 44.4 (0.9, 43.2-45.7, 4) 32.5 (0.7, 32.0-33.8, 4)
Black-crowned 
Night Heron
Tai 46.9 (2.9, 38.3-52.3, 41) 33.9 (2.2, 25.3-38.6, 41) 
DISCUSSION
The higher breeding productivity of Cattle and Little Egrets at the two Chinese sites, 
Poyang and Tai, than in Pakistan could be generally related to the larger availability of for-
aging habitats in China, where wet habitats were very widespread. Actually, the productiv-
ity of Cattle Egret, Little Egret, and Black-crowned Night Heron in China was at the top 
end of the range of values recorded in various parts of their range, while their productivity 
in Pakistan ranged among mean values (review by Rubolini & Fasola, in press). This high 
productivity suggests that no adverse agent (e.g. contaminants, Boncompagni et al., 2003; 
Sanpera et al., 2003) affected reproduction, and that breeding conditions (e.g. food avail-
ability) are very good.
The dark morph of the Little Egret in Karachi differed from the other, white morphs we 
studied, in chick condition, and breeding productivity, although some differences could be 
due to habitat since the dark morph was the only coastal population we studied.
ACKNOWLEDGMENTS
This study was conducted within the research project “Coastal and inland wetlands in China and Pakistan: colonial 
waterbirds as bioindicators of pollutant levels and effects” funded by the European Union (IC18-CT98-0294). We wish 
to thank all the collaborators to the fi eldwork, and particularly Umar Baloch, Liao Yingchun and Giuseppe Gaudenzi.
 – 374  –
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Productivité des aigrettes et hérons nicheurs en six sites asiatiques

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Productivité des aigrettes et hérons nicheurs en six sites asiatiques

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