It is thought that a lack of suitable egg-laying sites may limit populations of some lizards. Artificial egg-laying sites were created for the endangered Columbretes wall lizard Podarcis atrata (syn: P.hispanica atrata) endemic to the Columbretes (39º54’N, 0º41’E), an archipelago of uninhabited islets in the Mediterranean Sea off the Castellon coast (eastern Spain). It was hoped that this might help to increase lizard numbers in areas where scarcity of oviposition sites were considered a limiting factor to population size.
The study was conducted in 1993 on Columbrete Grande (13 ha). Artificial egg-laying sites comprised white plastic trays (20 x 15 x 7 cm) filled with dry volcanic sand from the island. Three types of surface (after noting where lizards naturally laid their eggs) were tested: five trays open sand; five with two flat 10 x 10 cm rocks placed on the sand; and five with a stone tile covering about 80% of the sand surface.
The containers were placed in two areas:
1) rocky, with little soil and vegetation; a low lizard density (about l00/ha); and a scarcity of
natural oviposition sites;
2) abundant soil with good vegetation cover (small shrubs, herbs and grasses); a high lizard density (about 800/ha); and apparently high availability of oviposition sites.
Trays were positioned 5-15 m apart on the ground (stones placed around them to make them more accessible to lizards) from 19 May to 30 July. About 0.6 1 of rain water was added to each initially, and thereafter 0.1-0.3 1 every other day. To quantify lizard activity in each nest, 5-min observations were made (morning and evening) on 19 days between 25 May and 8 July 1993.
To test suitability of conditions for incubation, three eggs (each from a different female) were placed in each tray and their survival monitored. Eggs that disappeared, broke or proved infertile were replaced with a new egg. Therefore, more than three eggs were placed in some trays.
All 15 artificial nests were regularly used for basking soon after placement. The presence of lizards, faeces and burrows was higher in the nests in area 2 than in area 1. Only one container (area 2) was used as an oviposition site; a 2-egg clutch (buried at 4 cm depth) which hatched successfully.
Modifications to the artificial egg-laying sites appear to be required to make them more attractive for oviposition, but the conditions themselves appeared suitable for incubation. Of the 60 eggs experimentally placed in them, one egg was infertile, two were broken when handled, and 10 were predated. Of the 47 remaining eggs, eight (17%) died inside the trays during the first month of incubation whilst 39 (83%) successfully hatched.
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