Census and Phenology of Breeding Waterbirds on the Islands of Khan, Tahmadon, Om-Al-Gorm and Nakhiloo in the Persian Gulf, Iran

Behrouz Behrouzi-Rad

Census and Phenology of Breeding Waterbirds on the Islands of Khan, Tahmadon, Om-Al-Gorm and Nakhiloo in the Persian Gulf, Iran

Behrouz Behrouzi-Rad

Islamic Azad University, Khuzestan Science and Research Branch, Ahvaz, Iran

Author

Correspondence author
International Journal of Marine Science, 2013, Vol. 3, No. 25 doi: 10.5376/ijms.2013.03.0025
Received: 02 Apr., 2013 Accepted: 01 May, 2013 Published: 06 May, 2013

Preferred citation for this article:

Behrouzi-Rad, 2013, Census and Phenology of Breeding Waterbirds on the Islands of Khan, Tahmadon, Om-Al-Gorm and Nakhiloo in the Persian Gulf, Iran, International Journal of Marine Science, Vol.3, No.25 193-200 (doi: 10.5376/ijms.2013. 03.0025)

Abstract

There are 4 islands Khan, Tahmadon, Om-Al-Gorm and Nakhiloo in the Mond Protected Area in Boshehr province in the Persian Gulf. This research was conducted in these islands from March 2008 to September 2012. Thirty four species of birds were identified in these Islands. Nine species were breeders. Bridled Tern Sterna anaethetus was dominant and indicates. The maximum population of this species was 29,461 pairs in 2006 in Nakhiloo. The Maximum breeding population of Lesser Crested Tern Sterna bengalensis was 11,783 pairs in 2012 in Nakhiloo, and Swift Tern Sterna bergii was estimated at 2,500 pairs in 2008. We estimated 92 pairs of Western Reef Heron Egretta gularis and 2,825 pairs of Crab Plover Dromas ardeola in 2005 in Om-Al-Gorm. The other breeders were Caspian Tern Sterna caspia, Gull-billed Tern Sterna nilotica, White-cheecked Tern Sterna repressa and Saunders’s Tern Sterna saunders. These four islands are the most important and sensitive habitat for breeding terns species Sterna sp, Crab Plover Dromas ardeola and Western Reef Heron Egretta gularis in the Persian Gulf. The islands have been identified as an "Important Bird Area" by Birdlife International proposed for protection as a part of the Mond Protected Area, now part of National Marine Park of Dayer, and suggested for to be classified as sensitive habitat for breeding seabirds.

Keywords

Breeding populations; Terns species; Crab Plover Dromas ardeola; Persian Gulf

Four islands of the delta of the Mond River (Figure 1), host a breeding population of the Western Reef Heron Egretta gularis, seven terns species (Lesser Crested Tern, Sterna bengalensis, Swift Terrn Sterna bergii, Bridled Tern Sterna anaethetus, Gull-billed Tern Sterna nilotica, Caspian Tern Sterna caspia, White-cheecked Tern Sterna repressa, Saunders Tern Sterna saundersi and Crab Plover Dromas ardeola (Scott, 1975; 1995; Behrouzi-Rad and Tayfef, 2008; Argayl, 1975; Evans, 1994). The islands hold over 1% of the regional population of Crab Plover Dromas ardeola of Middle East (Scott, 1995; Evans, 1994; Behrouzi-Rad, 2013). Also they have been identified as an "Important Bird Area" by Birdlife International(Evans, 1994), proposed for protection as a part of the Mond Protected Area (Harington, 1976), now it is part of National Park of Dayer, and suggested for classification as sensitive habitat for breeding seabirds (Behrouzi-Rad, 2008). These four islands are good representative examples of low-lying inshore islands characteristic of the Persian Gulf. The islands support important breeding colonies of seabirds and are also important for nesting sea turtle, including Hawksbill Turtle Eretmochelys imbericata (a globally threatened species, Scott, 1995).

Figure 1 Location of four islands in Persian Gulf

1 Methods and Material

1.1 Study Area

Four small, low-lying Persian Gulf islands located a few kilometers offshore c. 40 km south-east of the Mond River delta (Figure 1). Tahmadon (27°51'N, 51°27'E, 130 km SE of Bushehr) is 700 hectares with a chain of low vegetated dunes along its south-west margin and round the southern end (Figure 1). Om-Al-Gorm (or Ummal Karam, 27°00'N, 51°33'E, 133 km SE of Bushehr), the easternmost island, lies than 1 km off the main land and is c. 1.5 km long and 500 m wide (c.75 ha, Figure 1), with rocky shore in the south, sandy beaches in the north, and extensive dunes particularly in the west. The central basin of the island is completely covered by low scrub. Nakhiloo (27°49'N, 51°28'E, 133 km SE of Bushehr city, Bushehr is the center of Bushehr Province) the westernmost island, island and furthest offshore, is c. 35 ha (Figure 1), and composed mainly of sand with some rocky shores in the south and west. There is a small brackish pool near the south end of this island.The largest one is Khan (or Morghu, 27°29'N, 51°16'E, 108 km SE of Bushehr, Figure 1), covers an area of 800~1000 hectares (this variation in area is due to changes in tidal level), consisting of a broad expense of bare mudflats without any vegetation. All four islands are devoid of fresh water and uninhabited. These islands are hot in summer (45℃) and moderate in winter, their main inhabitants are the seabirds, but also sea turtles are present annually in spring and summer.The sea birds are considered to be the most important species to occupy the islands, endowed with good texture of soil, adequate plant covering and rich marine water. These islands are propitious environment for nesting and breeding for migratory waterbirds as well as sea turtles so that they are occupied annually in spring and summer.

1.2 Estimation of bird populations

Counts were done in mid-May every year in all islands, after all species established nests and laid egg. We estimated the area of the breeding habitat of the Bridled, Lesser Crested and Swift terns By GPS system. Nest numbers of Bridled Tern Sterna anaethetus, Lesser Crested Tern Sterna bengalensis and Swift Tern Sterna bergii were estimated using Sampling method by plots(20×20 m for Bridled tern(ten plot) and 1×1 m for the other two species(ten plot, Figure2) base don which the breeding population of these species was estimated(Blaber et al., 1998). The plots selected randomly in the breeding place of these three species. The nest with theeggs counted in the each plots. Counts were done only once during the breeding season of each year (between 18-25 May 2008-2012). The breeding time chronology was also observed. Total count method was used to obtain the census of the nests and breeding population of Crab Plover Dromas ardeola, Reef Heron Egretta gularis, White-cheeked Tern Sterna repressa, Caspian Tern Sterna caspia and Gull-billed Tern Sterna nilotica. This time was obtained by searching these breeding colonies since 2004-2008(Behrouzi-Rad and Taifeh, 2008).

Figure 2 Plot Method counts of the Lesser Crested and Swift terns’ nests in Islands

2 Results

2.1 Birds of the islands

Thirty three species of water and terrestrial birds have been identified in these islands since 2008-2012 of which 23 species were waterbirds and 11 species were landbirds (Table 1).

Table 1 Species of birds observed in Tahmadon, Khan, Nakhiloo and Om-Al-Gorm, 2008-2012 (Behrouzi-Rad, 2008; Scott, 1975 and 1995)

2.2 Species and populations of breeding birds on islands

Breeding species and maximum number of pairs estimated in 2008-2012 and 1975 are shown in Table 2. Eleven species bred in 1975 and 10 species in 2008-2012. Spoonbill Platalea leucorodia did not breed in 2008-2012 in the islands.

Table 2 Maximum population of breeding species in the islands

2.3 Situation of breeding birds in each island

2.3.1 Breeding species on Om-Al-Gorm (Ummal Karam)

Thirty species of birds were observed on Om-Al-Gorm in 2008-2012, (20 species of waterbirds and 10 species of landbirds; Table 1), six species of which were breeders in 2008-2012, and 9 species had bred in 1975 (Table 3, Scott, 1975; Behrouzi-Rad, 2013). The Om-Al-Gorm is a very important breeding area for Crab Plover and terns (Scott, 1995). A colony of 1,500 pairs of this species bred on sand dunes on this island in 1975 (Scott, 1995); the maximum colony size for Crab Plover was 2,825 pairs in 2009 (nearly twice that of 1975, Behrouzi-Rad, 2008). Seven species of terns nested on the Om-Al-Gorm in 1975 (Scott, 1975), four of them bred in 2008-2012 again, (Table 3 and Figure 3). The nesting location of birds on Om-Al-Gorm in 2008-2012 is shown in Figure 4. The Om-Al-Gorm holds over 20,000 seabirds in someyearsincluding over 1% of the regional population of Dromas ardeola, Sterna bengalensis and Sterna anaethetus (Scott, 1995, Table 3). Gull-billed Tern is a rare breeding migratory species of the Om-Al- Gorm, which appears to favour several reservoirs in Bulgaria during the breeding period. The Atanasovo Lake is the only breeding site. Between 4(Grossier, 1967) and 65 pairs bred in 1967 at Atanasovo Lake (Nankinov, 1989). The breeding population of Western Reef Heron increased from 26 pairs in 1975 (Scott, 1975) to 92 pairs in 2012 (Behrouzi-Rad, 2013). Bridled Tern was dominant in Om-Al-Gorm. The maximum population of this species was 20,620 pairs in 2008 and 1,000 pairs in 1975 (Table 3). The maximum breeding population of Lesser Crested Tern was 965 pairs in 2010 and 50 pairs in 1975, and Swift Ternwas estimated at 1,340 pairs in 2011 and 100 in 1975. Three species of Terns: Gull-billed Tern, Caspian Tern and Saunders’s Tern sterna saundersi did not breed in Om-Al-Gorm between 2008 and 2012, but there were 2, 5-10, and 5 breeding pairs respectively in 1975 (Table 3).

Table 3 Comparison of breeding bird populations on Om-Al-Gorm, Iran, from 1975 to 2012

Figure 3 Breeding population of birds in Om-Al-Gorm, 2008-2012 and 1975

Figure 4 Nesting areas of birds on Om-Al-Gorm 2008-2012

2.3.2 Breeding species on Nakhiloo

Twenty five species of birds were observed on Nakhiloo in 2008-2012, 19 species were waterbirds and 6 species were landbirds (Table 1). Eight species of birds had bred over the five year study in Nakhiloo (Table 4 and Figure 5). In 1975, five species of birds bred in this island (Table 4, Scott, 1975). Five species of terns, Western Reef Heron, Crab Plover Droma ardeola and Lesser Sand Plover Charadrius mongolus bred on Nakhiloo in 2008-2012. White Cheeked Tern had nested in limited number in the north of Nakhiloo and at place called Sheikh Karameh (Figure 6). Maximum breeding population (2008-2012) was 74 pairs in 2008. Bridled Tern bred in great numbers all over the island. GPS system estimated the area of the breeding habitat of this species 24.6 hectares. The total area of the island is 35 ha (Figure 6). Total breeding population of birds increased from 16,214 pairs in 1975 to 38,707 pairs in 2012, and from 15,340 pairs in 2008 to 38,707 pairs in 2012 ( more than twice). Three species of terns (Bridled Tern, Lesser Crested Ternand Swift Tern) were dominant and in Nakhiloo in 2009-2012. The maximum population of Bridled Tern was 29,461 pairs in 2010 (15,000 pairs in 1975), Lesser Crested Tern was 17,783 pairs in 2012 (10,000 in 1975), and Swift Tern sterna bergii was 1,488 pairs in 2012 (40 pairs in 1975) in Nakhiloo. Crab Plover and Western Reef Heron did not breed in Nakhiloo in 1975.

Table 4 Population of breeding species in Nakhiloo, 2008-2012 and 1975

Figure 5 Breeding populations of birds in Nakhiloo 2008-2012 and 1975

Figure 6 Nesting areas of birds on Nakhiloo, 2008-2012

2.3.3 Breeding species on Khan (Morghu)

Twenty species of birds were observed in Khan in 2008-2012. One species, the Hoopoe Upopa epope was a landbird, terrestrial and 19 species were waterbirds, eight of which were breeders (Table 5 and Figure 7). Lesser Crested Tern and Swift Tern were dominant and indicate in 2008-2012 in this island. The maximum breeding population of Lesser Crested Tern was 4,345 pairs in 2009, but only 300 pairs in 1975 (Scott, 1975) and maximum population of Swift Tern was 2,500 pairs in 2008 but only 40 pairs in 1975 (Scott, 1975). Bridled Tern was dominant in 1975 with 5,500 breeding pairs (Scott, 1975), but this species did not breed in Khan in 2008-2011, only in 2012, when 325 pairs bred in this island. All species bred at the southern part of island (Figure 8). The total breeding population of birds decreased from 5,917 pairs in 1975 to 2,579 pairs in 2012, a 50% reduction of the population (Figure 7). Spoonbill bred in Khan in 1975 but it neither occurred nor bred in Khan or in the other three islands in 2008-2012. There were only 5 breeding pairs of Crab Plover in 2008 in this island. In 1975, 4 species of terns and the Spoonbill bred there, and in 2008-2012 six species of terns and the Western Reef Heron bred in Khan, in fact, the Spoonbill was replaced by the Western Reef Heron in 2008-2012. The Caspian Tern breed only in Khan among the four islands. The maximum breeding population of this species was 145 pairs in 2011. The breeding population of this species is low in the Persian Gulf islands. May be an approximate number for the species can be given, with a reference.

Table 5 Population of breeding species in Khan (Morghu) 2008-2012 and 1975

Figure 7 Breeding population of birds in Khan (Morghu) 2008-2012 and 1975

Figure 8 Breeding places of Birds on Khan (Morghu) Island2008-2012

2.3.4 Breeding species on Tahmadon

Nine species of birds were observed in Tahmadon in 2008-2012. All species were waterbirds. There were no breeding species of birds in Tahmadon since 2008-2012. There is not any official report of breeding of birds in this island, but local people information shows many tern species have nested in this island before 2004. In 2004 a Pair of Golden Jackals Canis aureus entered the island during low tide (this island is located about 500 m from the mainland and water depth during low tide is about 50 cm, and these animals could swim and enter the island) and likely disturbed the breeding birds. The game guard of the Department of the Environment of Bushehr removed the Golden Jackal in 2005, but the birds did not return to the Tahmadon for breeding.

2.4 Breeding time table of birds in the islands

Breeding bird species arrival to the islands starts in early April continuing to early May (except Western Reef Heron, which arrives to the island on mid-March, egg lying starts in late March), egg lying begins in early May and all species leave the island on September. There are a few migratory species of waterbirds in autumn and winter in these islands (Table 6).

Table 6 Time table of breeding species of birds in the islands

The colony of Terns is located in the three flowing environment in these islands:

Sand dunes beaches facing the sea (Lesser Crested and Swift Terns, Figure 2, Figur 4 and Figur 6).

Central part of islands covered by Halophyte vegetation (more than 3 0% by Bridled Tern, Figure 1) and without vegetation (White-cheeked Tern).

2.5 Species with important population proportions (1% or more of population).

Table 7 shows the breeding species of birds with populations at or over 1% (the threshold level of the estimated world population of a species in order for the area to be considered as internationally important according to the criteria of the Ramsar Convention.

Table 7 Species with important population proportions (1% or more of world population) breeding in the area

3 Discussion

Terns form the main animal group heavily dependent on the islands for their continued existence. There are many species of this seabird group in the Persian Gulf, but three in particular nest in vest number on the islands. These are the Lesser Crseted Tern Sterna bengalensis, Swift Tern Sterna bergii and the Bridled Tern Sterna anaethetus. All three species occur together on most of the Persian Gulf islands (Tuck, 1974), but each has distinctive nesting habitats. Besides terns, which breed in summer, several other species of bird use the islands for breeding, notably Crab plover Dromas ardeola, Reef heron Egretta gularis, Caspian Tern Sterna caspia, Gull-billed Tern sterna nilotica,LesserSand Plover Charadrius mongolus,and land birds such as Crested Lark Galerida cristata (Harington, 1976). The Crested Lark Galerida cistata did not breed in 2008-2012 in Om-Al-Gorm, Nakhiloo, Khan and Tahmadon islands. This species is very common and breeder species at Persian Gulf coasts. During spring and fall migration the islands are visited by a number and variety of shore and land birds (Table 1). The islands hold over 1% of the regional( Regional population in Middle east) population of Crab Plover Dromas ardeola, Lesser Cressted Tern Sterna bengalensis and Bridled Tern Sterna anaethetus (Scott, 1995; Evans, 1994; Behrouzi-Rad, 2013). The islands have been identified as an "Important Bird Area" by Birdlife International (Evans, 1994), proposed for protection as a part of the Mond Protected Area (Harington, 1976), now it is part of National Marine Park of Dayer, and suggested for to be classified as sensitive habitat for breeding seabirds (Behrouzi-Rad, 2008). These four islands are good representative examples of low-lying inshore islands characteristic of the Persian Gulf. The islands support important breeding colonies of seabirds and are also important for nesting sea turtle, including Hawksbill Eretmochelys imbericata, a globally threatened species (Scott, 1995; Evans, 1994). Some terrestrial animals also inhabit the islands. These include a considerable variety of insects, spiders, which have not yet been studied in any detail, a couple of species of lizards, and innumerable Black Rats. Recent species is a native in Iran, but there is not enough information (how and when) about entrance of Black Rats to the islands, but local people information shows this species entered to the islands by fisherman boats.

Natural predators, namely the Black Rat Rattus rattus, Ruddy Turnstone Arenaria interpress and Crab Plover Dromas ardeola frequently interfere with the nesting success of terns, also sometimes some gull species, specially Lesser Black-backed Gull Larus fuscus that feeds on eggs and chicks of terns. Rattus rattus is often noted as a predator of Cory’s Shearwater chicks (Jean-Pierre Biber, 1989). Predation of chicks by Black Rats is noted where their density is high (Jean-Pierre Biber, 1989). It is also believed that some colonies have been deserted in the past due to continuous disturbance of breeding site by some fishermen. Nakhiloo, Om-Al-Gorm, Tahmadon and Khan Islands are good representative example of low-lying inshore islands characteristic of the Persian Gulf. The islands support important breeding colonies of Dromas ardeola (Maximum breeding population 2,825 pairs in Om-Al-Gorm) and Terns (Sterna sp.). The Maximum number of Breeding population of birds which have been censuses in recent years in the islands were 17,783 pairs in Nakhiloo for Lesser Crested Tern (Table 3), 2,500 pairs for Swift Tern in Khan (Table 5), 29,461 pairs for Bridled Tern in Nakhiloo, 700 pairs for White-checked Tern in Om-Al-Gorm and 92 pairs for Western Reef Heron in Nakhiloo. The islands are managed by a National park authority. They are Sensitive area for breeding population of Terns, Western Reef Heron, Crab Plover and Hawksbill Turtle (The Globally Threatened Species). Within the Persian Gulf, Lesser Crested Tern and Bridled Tern are most abundant in the Nakhiloo and Om-Al Gorm. The same species of Terns breed in each of the three islands. (Table 3, Table 4 and Table 5). The fluctuations of the number of breeding population could be due to variation in the local environment of the islands (Figure 2, Figure 4 and Figure 6). During 2008-2012 the tern species have nested in the islands, with patterns suggesting the influence of some common factors, acting on a local scale. An increase of Bridled Tern occurred throughout the islands till 2010 and then declined again; this could be attributed to the food and security provided during breeding time. It seems the populations of terns move between the islands. The number of colonies and the average number of nests per colony (Table 3, Table 4 and Table 5) are extremely stable between the islands, and are presumably determined by the local environment. At present, the offshore islands of the Persian Gulf, with their coral reefs, present a picture of unspoiled beauty. Their plant and animal population are rich and unique, and are exceptionally beautiful and distractive as well as being of great scientific interest. Much of the beauty and uniqueness of these sites, however, result from the fact that they have so far remained relatively free from human interference. They represent a valuable, fragile and irreplaceable resource. The Nakhiloo, Tahmadon, Khan and Om-Al-Gorm islands are a part of Dayer National Park and have few known threats.

Acknowledgements

This research project has been financially supported by the Department of the Environment Office of Bushehr Province. We are grateful to DoE of Bushehr for supporting this project. I would also like to thank the Department of the Environment personnel of Dayer National park Office who helped in the counts of the terns population and assisted with transportation on islands.

Reference

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