Robert Humair Allowing
Robert Humair Allowing for the limiting fact that the data pool was not very extensive, I made the following observations: The number of females (89) is almost equal to the number of males (91); I cannot however state whether this is a true reflection of the sex ratio in the wild. Males are heavier on average (5.887 kg) than females (5.554 kg). Male specimens are longer on average (41.09 cm) than female South American yellow-footed tortoises (38.44 cm). Females are proportionally more elongate (0.947) than males (0.859). Female specimens are higher than male ones; the latter are rather flat whereas females have a rather domed shell. I have come to the conclusion that the body mass index (BMI) is inconclusive in Chelonoidis denticulata: while it increases with weight in females, it is variable in males, even though it should be expected to be uniform in either sex. The Jackson Graph is a simple means for evaluating the physical condition of tortoises. It is based on Jackson (1980) who noted a strong correlation between the physical condition of individual Testudo graeca and Testudo hermanni and the ratio between their weights and carapace lengths. While it attracted criticism from some quarters, numerous discussions eventually led to McArthur (1996) finding that the Jackson Graph was well suited for evaluating the physical status of Mediterranean tortoises from a veterinarian perspective. The index required according to Jackson is calculated by dividing the weight of a tortoise (in grams) by its carapace length (in millimetres). I observed that the Jackson Graph would increase in a linear manner in Chelonoidis denticulata, but that it was difficult to identify specimens that were outside of the normal range. Females Males Fig. 1. Body mass indices (BMI) of 89 female and 91 male Chelonoidis denticulata. This index is derived from the weight of a tortoise (g), divided by its plastron length (cm); vertical = BMI value, horizontal = plastron length. 24 RADIATA 22 (4), 2013
South American Yellow-footed Tortoise, Chelonoidis denticulata Female minimum Female maximum Male minimum Male maximum Fig. 2. Jackson Graph, calculated for 89 female and 91 male South American Yellow-footed Tortoises; vertical = Jackson Graph, horizontal = carapace length. Comparisons between South American Yellow-footed Tortoises living in the wild and those in my care I wanted to find out whether the measurements taken from the Yellow-footed Tortoises in my care were similar to those of specimens living in nature. For this purpose I took the weights of the Chelonoidis denticulata in my care and compared them to specimens of the same sex and similar sizes living in the wild (Parque Quistococha near Iquitos, Peru). Free-ranging females Females in my care Fig. 3. Comparison of free-ranging female South American Yellow-footed Tortoises with specimens in my care; vertical = weight (kg), horizontal = length (mm). The two females of 690 and 740 mm in carapace length, respectively, in my care were not taken into consideration, as I was unable to find female specimens of similar dimensions in nature. RADIATA 22 (4), 2013 25
