Odonata (Insecta) at a wadi Pool near Nizwa, northern Oman

LC The present paper describes odonates recorded over an extended period at a wadi (valley) pool in the southern foothills of the Jebel Akhdar mountain range, near Nizwa, northern Oman. In all, 68 visits of several hours each were made to the pool during 23 months between March 2012 and June 2014. Cowan & Cowan (2013) described the wadi pool and odonate species seen there from March 2012 to June 2013. Here we present monthly occurrence of odonates, including mating and egg laying, over the full period for the 14 species observed including four first seen after June 2013.

The damselflies and dragonflies, Odonata, of Oman are known largely through the collection of specimens and photographic records. In the latest checklist of the odonate fauna of Oman, Schneider & Dumont (1997) recorded 40 species, collating information from 1912 onwards. Two species have been added recently. Ischnura fountaineae Morton, 1905 was photographed in northern Oman (Reimer et al. 2009) and Tholymis tillarga (Fabricius, 1798) was reported from Dhofar (Ball 2014), over 1000km to the south. Oman is largely a desert country with a mainly arid climate. Rainfall in the north is in the winter though monsoon-induced summer rainfall sometimes occurs (e.g., Fisher et al. 1999). dramatically over time due to rainfall, or the lack of it, in the wadi's catchment. The southern and eastern sides of this apparently permanent pool are a popular picnic site especially at weekends.

Methods
All our identifications at the pool (Table 1) were based on digital photos, allowing for later deliberation and confirmation. All photos were taken by E.M.C. using a handheld Sony Cybershot compact camera. The data includes the monthly occurrence of odonate species, presenting the number of visits in a month in which we photographed the species. No visit was made in June, July, November, December 2012 or July 2013. The occurrence of mating and egg laying by month except for the 'no-visit' months are also presented. Every datum is supported by a 'voucher photo' in E.M.C.'s personal collection. Identification was facilitated in many cases by reference to Dijkstra & Lewington (2006), the field guide to the odonates of Europe and western Turkey, Cyprus and northwestern Africa. Also useful were wellillustrated papers on the odonate fauna of the adjoining United Arab Emirates (Giles 1998;Feulner et al. 2007;Reimer et al. 2009), the Asia/Africa Dragonfly website (www.allodonata.com), Samways (2008), Subramanian (2009), and Smallshire & Swash (2014).

Results
Table 1 lists the 14 odonate species (Images 2 to 31) we recorded at the pool. Images 2 to 30 were taken at the pool during our study period and identification notes are given in their captions. Table 2 presents monthly  occurrence whilst Table 3 notes the months when mating and laying were observed and photographed. A variety of different exuviae were observed around the pool. Large Anax-type exuviae were most frequently recorded but usually several other types of exuviae were present sometimes in large numbers on the poolside  Trithemis kirbyi was the only species recorded in all 23 months in which observations were made. On occasion this species was very numerous (in their hundreds) and generally it was the most numerous species at the pool. On very hot afternoons, T. kirbyi crowded into the shade in large groups. It was the sole species we located in August and September 2012 when the pool was deeply flooded after summer rains and water was fast flowing over the head dam wall.
Both zygopteran species were recorded mating and ovipositing. A popular mating site for Ischnura evansi was in the lower branches of a sidr tree Ziziphus spinachristi (L.) Desf. that overhangs the pool. Photographic data showed that one pair of I. evansi was in copula on the same branch for more than two hours (Image 3). Female Ischnura damselflies seen laying (they oviposit without a male in attendance and are notoriously difficult to identify to species) were presumed to be Ischnura evansi (Image 4) as no other Ischnura species was recorded at the pool (see Table 3). Pseudagrion decorum also mated regularly (Image 6) but chose a wider range of sites-the branches of the sidr, but also twigs or rocks in the pool. Oviposition (Image 7) took place in the way described by Feulner (2001) with the pair mating and then descending in tandem on a stem or into a weed patch with the female below the water surface. Oviposition by this Pseudagrion species was usually observed as lasting for 1-2 minutes rather than up to five minutes submerged as noted by Feulner (2001).
Reproductive behaviour was recorded for eight of the anisopteran species. Both Orthetrum chrysostigma and O. sabina were recorded in mating wheels (Images 15, 17) and then ovipositing on many occasions. Anax imperator was not seen mating but females were observed on many occasions ovipositing (Image 8, Table  3). Often two or three females were recorded but, on one occasion, seven females were seen ovipositing simultaneously in patches of floating weed or other vegetation in the pool. Sometimes, when several males were patrolling the pool, one pursued a female but she flew along pulling down her abdomen into a laying pose, indicating rejection of mating (Corbet 1999: 471-472). Crocothemis erythraea was observed mating on many occasions in winter/spring 2014. As a pair began to copulate in flight over the pool, there was a characteristic   wing-clattering sound. They remained in copula for much less than a minute flying over the pool, sometimes settling momentarily on a stone, twig or the bank (Image 20). They quickly break apart with the male guarding the female during oviposition against other males which aggressively attempted to intrude.

Discussion
We recorded 14 odonate species, all included in the checklist of Oman's Odonata by Schneider & Dumont (1997). All were globally assessed as Least Concern (IUCN 2013) except for Paragomphus sinaiticus which is globally Near Threatened (Boudot et al. 2013a).
Our phenological and reproductive behaviour data suggest that there is a core odonate community at the pool consisting of eight permanently resident species, each present on over 70% of our visits. This comprises two coenagrionid species (Ischnura evansi, Pseudagrion decorum) and Anax imperator, Orthetrum chrysostigma, O. sabina, Crocothemis erythraea, Trithemis annulata and T. kirbyi. Other species were recorded on less than 50% of visits and could represent nomadic (wanderer or migrant) individuals, although opportunistic egglaying may occasionally occur. Paragomphus sinaiticus was recorded at the pool on 41% of visits and Trithemis arteriosa 37% of visits, though we did not record reproductive behaviour for either of these two species. Diplacodes lefebvrii was present on 23% of the visits and one pair was observed mating and laying in the pool in Table 3