Head-started Agassiz’s desert tortoises Gopherus agassizii achieved high survival, growth, and body condition in natural field enclosures
| Autor: | Kenneth A. Nagy, Brian T. Henen, L. Scott Hillard |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2020 |
| Předmět: |
0106 biological sciences
Captivity 010603 evolutionary biology 01 natural sciences emergence success Condition index Animal science Survivorship curve lcsh:Botany condition index lcsh:Zoology Juvenile Carapace lcsh:QL1-991 Hatchling Nature and Landscape Conservation density effects Ecology Wildflower 010604 marine biology & hydrobiology Biological Sciences lcsh:QK1-989 shell hardness index Hay predation survivorship Environmental Sciences |
| Zdroj: | Endangered Species Research, Vol 43, Pp 305-321 (2020) |
| ISSN: | 1613-4796 1863-5407 |
| Popis: | We measured survival, growth, and body condition of 8 hatchling cohorts of desert tortoisesGopherus agassizii(living in predator-resistant outdoor pens in the Mojave Desert, California, USA) over 11 yr to evaluate head-starting methods. At 11 yr of age, 7 times as many of the first cohort had survived than if they had been free-living tortoises. Subsequent improvements in predator control, food and water supplementation, and pen structure increased survival from 7 to 10 times that under wild conditions in younger cohorts. Annual survival averaged 96%. Carapace length (CL) increased 6.95 mm yr-1, similar to that of free-living tortoises. Annual growth rates varied with calendar year (possibly reflecting food and water supply), age, cohort (year hatched), mother, and in 4 dry years, with crowding. Most of the first cohort grew to a releasable size (CL >100 mm) by their 9th year. Body condition indices remained high, indicating little dehydration despite droughts in 8 of the 11 years, because irrigation offered drinking opportunities. Head-started tortoises developed fully hardened shells (≥98% of adult shell hardness) earlier (10.1 vs. 11.6 yr), but at a larger CL (117 vs. 104 mm) than did free-living tortoises. Selective feeding in head-start pens decreased subsequent germination of favored wildflower species, apparently by reducing the natural seedbank. Consequently, we reseeded and irrigated each autumn to promote subsequent spring food supply. We irrigated in early summer to enable drinking and ensuing consumption of dry, dead plants and Bermuda grass hay, a supplement. These procedures can greatly improve juvenile survivorship, and increase numbers of hard-shelled, midsized juveniles to help augment wild populations. |
| Databáze: | OpenAIRE |
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