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Body Condition Index
Body condition indexes are an extremely useful tool for wildlife monitoring. They provide
information on the health of a species and are known to affect a number of survival related
behaviours.
The most directly relevant impact of body condition is frog reproductive success. Studies into the
male calling behaviour show correlations between a frogs condition and the frequency, volume and
length of their calls (21).
Almost all anurans use calling as their primary mate attractant behaviour. The quality of their calls is
known to affect potential matings for male Neotropical frogs; and thus reproductive success. These
calls also serve to defend a territory used for hunting; and in some species raising young.
Clutch size and proportion of eggs which survive to adulthood is strongly dependant on mothers’
body condition for all amphibians (22). Among those species of frog which provide food for their
tadpoles female body condition is even more important; for reproductive success.
A study into three species of European frog determined that jumping distance is dependent on body
size and weight, rather than proportional hind limb length, larger frogs are able to jump further (23).
Frogs ‘leap’ to escape from threats. Some Neotropical frogs use toxins, and/or warning colours, to
deter predation; but for most species jumping is their only form of predator avoidance.
Monitoring body condition indexes is for understanding the health of the current population and
predicting patterns in the populations’ future. Body condition in frogs is impacted by the presence of
several different threats; it is often the first indication of wider problems.
Habitat loss and degradation will affect frog body condition (24). Activities such as logging,
witnessed in the study area during this survey, disturb animal populations causing them to relocate.
The energy cost of moving to and establishing a new territory, or of remaining in a degraded one,
reduces the body condition index of frogs.
Fragmentation of habitat is a big threat to global amphibian populations. While the problem usually
occurs when the habitats, used for aquatic tadpoles and terrestrial adult amphibians, are separated
impacting breeding; habitat fragmentation will also impact body condition (25).
Significant decreases in the invertebrate populations will lower frog body condition by increasing
hunting effort: gain ratio. Broad monitoring of invertebrates is very difficult to survey at an
ecosystem, or even habitat level, as the populations are huge and fluctuate widely (26).
Pollution does not directly impact frogs’ body condition until it has reached very high levels.
Pathogens and parasites, which are more common in amphibians from polluted areas (27), do lower
a frogs body condition index.
Monitoring of frog body condition provided important information the population and condition of
their environment. How we measure the body condition of animals in the wild will affect the
accuracy of any conclusions drawn from the data. Body condition indexes (when calculated as
weight divided by body measurements) are a reasonably accurate system for measuring body
condition (6).
The data collected can be compared to determine which individuals are in better, or worse,
condition relative to the others. Body condition indexes cannot be compared between organisms
that have significantly morphologies, e.g. frogs and newts, when calculated as in this paper. To
compare different morphologies’ weight divided by volume (height x length x breadth) can be used
but is still far more accurate when comparing similar organisms (7).
Further studies of frogs in this area should either measure frogs height, in order to calculate volume,
or only measure length and weight. The unused width measurement increase handling time and
resulting animal stress.