The Horsfield's tortoise: Testudo horsfieldi (GRAY) 1844 - A brief review of it's biology, ecology & captive breeding
A. C. Highfield
This paper describes the captive breeding and maintenance of Testudo horsfieldi (GRAY) 1844, a species which was imported into Britain in considerable numbers during the late 1960's. The largest importation occurred between 1965 and 1971 when a total of 119,319 Horsfield's tortoises were received at U.K. ports. The species is not easy to maintain successfully and the vast majority of those early imports have not survived in the long-term. The animal is now rarely encountered in captive collections and captive breeding is very infrequently reported.
Description:
Distribution:
Systematics:
Testudo baluchiorum ANNADALE 1906:75, 205, pl.2 fig.1 (type-locality: Baluchistan[Holotype in Calcutta])
Whilst the nomenclature of the above is relegated to the synonymy, the description and report provide useful details of Testudo horsfieldi in Baluchistan.
Habitat and ecology:
Reproductive behaviour:
In the former soviet part of their range, Terentjef and Chernov (1949) report that mating commences in March and lasts until June, with deposition in May and the first weeks of June. Hempel (1988) notes that mating commences almost immediately upon emerging from hibernation.
Terentjev and Chernov (1949) note that two to three clutches of eggs may be laid per season, and this observation is confirmed by the behaviour of T. horsfieldi in the present author's collection. In the former Soviet Union, Sergeev (1941) reported 4 clutches per year. Hempel (1988) records that a captive female laid several clutches of 2-4 eggs per clutch and in the USA, Slavens (1989) observed a large captive female lay 2 clutches of 7 and 9 eggs at the end of August and another clutch of 3 eggs in September. According to Mylnarski and Mertens (1971) an individual female may lay as many as 20 eggs per season in 3 or more clutches.
Reported egg dimensions appear to vary considerably. Werner and Werner (1980) observed eggs which measured 43 X 30mm and 42 X 30 mm. Three eggs currently residing in the present author's incubator measure 41 X 30 mm, 41 X 29. 5mm and 40.5 X 30 mm respectively. An earlier clutch laid by the same female produced eggs measuring 47mm long X 34mm wide (Highfield, 1990). Typical egg weight (at deposition) ranges from 22-25g, although some viable eggs may weigh as little as 16g.
The eggs hatch under artificial incubation conditions identical to those found suitable for other circum-Mediterranean Testudo species: 30-31° C at circa 80% relative humidity. In these conditions, hatching may be expected at between 61-75 days. Of three eggs laid by the present author's female on 20th July 1991, one hatched on the 5th of September and a second on the 14th September. The third egg was infertile. The incubation temperature in that instance was maintained at a very constant 30.5°C (Highfield, 1991).
At emergence, hatchlings typically measure some 42-50 mm in carapace length and weigh between 18-23g. Growth is fairly rapid for the first 12 months. After one year, 70 mm SCL and a weight of 80g may be attained.
Dietary management is as for other Testudo species, with a low protein, high calcium, high fibre diet the primary key to successful and deformity-free growth. This author finds the dietary supplement 'Nutrobal' to be ideally suited to rearing juvenile tortoises. Environmentally, the Horsfield's tortoise prefers warm, dry and well ventilated conditions. Enclosed vivaria are not well tolerated. An outdoor terrarium situated in a sunny position, with a slope for basking purposes is ideal. As noted previously, these tortoises are prodigious and industrious excavators: the enclosure must be checked regularly for 'escape tunnels' - keeping Horsfield's tortoises secure is no easy task. They are proficient in the art of escape and are extremely agile.
Sexual maturity is believed to be attained in 7-10 years (Roberts, 1975, Terentjev and Chernov, 1949).
REFERENCES
First published: 1992 - ASRA Journal
The carapace is rounded, and is almost as broad as long; the tortoise has an overall 'stocky' appearance; the forelimbs have well developed claws with 4 toes per foot; head and limbs are coloured a yellowish brown; the shell is a greenish or olive brown with darker brown, diffuse patches; there is no movable hinge on the plastron, which is rigid and inflexible; the tail possesses a terminal claw similar to, but not quite as pronounced as Testudo hermanni. Females are typically larger than males, the largest verified specimens having been recorded as attaining 22cm Straight Carapace Length (SCL). Terentjef and Chernov (1949) report a specimen of 286mm SCL which is said to be deposited in a Russian Museum. Unfortunately, the whereabouts of this specimen is now uncertain. The plastron of males is barely convex, but males do possess a much longer tail than females and hence may readily be identified.
The Horsfield's tortoise is an Asiatic species of wide zoogeographic distribution, albeit at low individual population densities. In a recent study conducted in Southern Turkemen, Makeev, Bozhanski and Frolov (1986) provide estimated density figures of 308 animals per square kilometre, or 3 animals per hectare. In other parts of its range the density is believed to be considerably lower. The reported range includes Baluchistan, Pakistan, Eastern Iran, Afghanistan, Western China to the Caspian Sea in the former USSR.
No review of T. horsfieldi would be complete without reference to the controversy surrounding this tortoise at generic rank. Khozatsky and Mylnarski (1966) have suggested that Testudo horsfieldi be removed from the Testudo genus and have proposed including it within the monotypic genus Agrionemys. The key characters relevant to this separation include the immobile plastron, the anterior and posterior claw configuration and the suprapygal format (metacarpals). The authors of the proposed genus take the view that this combination of primitive characters and advanced specialisations indicates that Testudo (or Agrionemys) horsfieldi is conclusively distinguished from all living and fossil testudines. They are undoubtedly correct in drawing attention to the inconsistent diagnostic criteria for Testudo; in particular the fixed plastron (which horsfieldi shares with hermanni) is significant. However, at present there is no general consensus on the issue. Testudo horsfieldi has also acquired an interesting synonym:
In the former USSR this species occurs principally on sandy steppes, although loamy habitats have also been recorded. In Pakistan, Minton (1966) found T. horsfieldi exhibited a preference for grassy areas close to springs in generally rocky and hilly terrain. This species is well known for its digging abilities; tunnels up to 2m long with widened chambers at the end are frequently excavated in steep hillsides or under overhanging stones (Mylnarski and Wermuth, 1971). The disused burrows of rodents are also colonised and adapted: the burrows of the Marmot and Hedgehog appear to be particularly favoured (similar behaviour has recently been observed by this author in relation to arid South Moroccan habitats of T. graeca graeca where abandoned Hare burrows are used by aestivating tortoises (Highfield, in press). This tortoise is reported not to occur in coastal areas, preferring instead the mountains inland. In the former USSR the species is active for only 3 months of the year, usually March, April and May. From late May onwards activity sharply decreases and the tortoises spend most of their time hidden in their burrows. In the northern parts of its range, T. horsfieldi hibernates in winter deep within its burrow; in the southern parts of its range aestivation occurs in summer (Ernst and Barbour, 1989). In Pakistan, captive tortoises were observed to bury themselves from October to March and aestivation occurred from June to August (Roberts, 1975). This tortoise is also found at unusually extreme altitudes: Minton (1966) found them at between 1,600 and 2,300 m. A more typical altitude in the former soviet sector of their range would appear to be between 800m. and 1,600 m.
Male T. horsfieldi are noted for their unusual pre-nuptial display. This consists of the male circling the female and biting at her head and legs, followed by a strange head movement made with the neck fully extended and semi-rigid. The head is jerked up and down in rapid succession whilst staring the female in the eyes. This behaviour (minus the biting) is very similar to that observed in Chelonoidis (Geochelone) carbonaria. Mating is accompanied by high-pitched vocalisations by the male. During the mating period males are mutually antagonistic and may fight viciously.