On the Incubation Biology of the Spur-Winged Plover Hoplopterus Spjnosus (Aves: Charadriidae) in Israel

ISRAEL JOURNAL OF ZOOLOGY, Vol. 34, 1986/87, pp. 155-157 ON THE INCUBATION BIOLOGY OF THE SPUR-WINGED PLOVER HOPLOPTERUS SPJNOSUS (AVES: CHARADRIIDAE) IN ISRAEL HANA CZACKES-RADO AND YORAM YOM-Tov Department of Zoology, Tel Aviv University, 69978 Tel Aviv, Israel Little has been published on the incubation biology of the spur-winged plover and much of what does exist is quoted as a personal communication from S. Su-Aretz (Cramp & Simmons, 1983). The observations which we report here will partially fill the gap. Our observations were carried out in the Tel Aviv-Ramat Gan Safari Park near Tel Aviv. The area is almost flat, has several small open groves, open grass and a large pond. About 20 pairs and 40 flock birds of wild spur-winged plovers live in the park, mainly near the pond, but also in the groves. Observations were made during the springs of 1982 and 1983. Numerical values are given as mean±standard deviation. Biology. The birds live in pairs throughout the year. Copulations were observed in the third week of March and continued even after hatching of the chicks. Nests were built chiefly near the pond. Both members of the pair participated in nest building by leaning on the breast and scratching the ground with their legs, pushing the soil in all directions and later pressing their breasts to the ground while making side movements until a 7-10 em diameter, 0.5-3 em deep depression was formed. The birds lined it with small pieces of grass. Many nests were made near resting sites of large animals: 1.5 m from a preferred basking spot of a crocodile, Crocodylus niloticus; near the lions, Panthera leo; and in the enclosures of spotted deer, Rusa axis and Indian elephants, Elephas maximus. Females laid eggs a day or two after the nest had been formed. Mean clutch size was 2.94 (n = 18); five nests contained 2 eggs, 9 contained 3 eggs and 4 nests contained 4 eggs. The laying interval was 2 days. Clutches of 2 eggs are smaller than the minimum clutch size of 3 eggs reported by Cramp and Simmons (1983), but Johnsgard (1981) reported clutches with ranges of 2-5 eggs. Mean egg dimensions resemble those reported by Cramp and Simmons (1983), i.e. length= 40 mm, breadth = 29 mm. The individual variation in egg dimensions within a nest was smaller than the overall variation (coefficient of variation in egg length was 3.3% and 4.25%, respectively; in breadth 1. 7% and 3.5%, respectively, n = 5 nests and 18 eggs). Mean fresh egg mass was 16.6±1.0 g (range 14.8-18.2 g; n = 21), similar to the mass calculated by Schonwetter (1962). The first egg was laid on 7 April and the last appeared on 15 May. In Israel, however, laying occurs until July (H. Mendelssohn, pers. commun). In one case Received 23 June 1985 and in revised form 22 October 1985 156 H. CZACKES-RADO ANDY. YOM-TOV Isr. J. Zoo!. where the eggs disappeared, the female started laying a replacement clutch 10 days later. Incubation started after laying the second egg and not the last as reported by Cramp and Simmons (1983) and as is often the case. The parents shared the incubation duties equally. The duration of an incubation turn was 33± 12.5 min (n = 9). However, the incubating parent did not sit continuously on the eggs; it rose on average every 12±8 min (n = 12), mainly in order to defend its territory against intruders of its own and other species. This high intrusion rate is probably an outcome of breeding in the crowded park. Hatching is spread over 24-48 hours. Hatching success in the field was observed for only 6 nests, where all eggs hatched. Physiology. Egg mass loss during mcubation was measured for 20 eggs removed from 6 nests and transferred to the laboratory. They were incubated at 35± 1°C and a relative humidity of 52±4%. Eggs were weighed every day or two with a Mettler balance to a 0.5 mg accuracy from the 5th day in the incubator. This procedure continued for 32 days. Three additional eggs were taken from their nests every 3 days for weighing, but otherwise were incubated by their parents. Twelve of the 20 laboratory eggs hatched: 6 after 22 days, 2 after 26 days, 1 each after 27 and 28 days and 2 after 30 days. The last two hatchlings were deformed. Normal incubation length in this species is 22-24 days (Cramp and Simmons, 1983). The rate of daily mass loss of the 10 artificially incubated eggs, from which normal young hatched, is given in Figure 1. There was no difference in the rate of daily mass loss (of fresh egg mass) between the hatched and unhatched eggs 0 '}. 5 .,- Ill Cl ~ 16 .:: .:: Cl Cl ·;; ~ ~ 10 Cl Cl UJ 15 100 300 500 Incubation , hrs. Fig. I. Water loss during incubation of lO artificially incubated eggs which hatched after 22-28 days. Means±SE. Y = 17.22-0.0047 X; r = -0.9965. Y=egg mass, g; X=incubation length, hrs. .

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