Measurement Error Associated With External Measurements Commonly Used in Small-Mammal Studies

Blackwell, Grant; Bassett, Suzanne M.; Dickman, Chris R.

doi:10.1644/05-mamm-a-215r1.1

Cited by 39 publications

(31 citation statements)

References 25 publications

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“…This was because only stomachs, and not entire carcasses, could be collected from the remaining cat samples. All measurements were taken three times to increase precision, following the recommendations of Blackwell et al (2006). The stomach and intestines were then removed from the cats and placed in specimen jars in 70 % ethanol for preservation.…”

Section: Cat Collection and Processingmentioning

confidence: 99%

Diet of the feral cat, Felis catus, in central Australian grassland habitats during population cycles of its principal prey

Yip

Rich²,

Dickman

2014

Mamm Res

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Foraging theory predicts that animals should forage so as to maximize their net rate of energy gain or to minimize their risk of starvation. In situations where prey numbers fluctuate dramatically, theory predicts further that foragers will eat 'optimal' prey when it is abundant but expand their diet to include other prey types when the optimal prey is scarce; this is the alternative prey hypothesis. Here, we test this prediction by analyzing the diet of a mammalian predator, the feral house cat Felis catus, during periods of scarcity and abundance of the long-haired rat Rattus villosissimus. We also investigate whether the body condition of feral cats differs during different stages of the prey population cycle. Feral cats were shot during culling operations in semi-arid grassland habitats in central Queensland, Australia, and the stomach contents later identified. We found that the body condition of feral cats did not differ between phases of the prey population cycle, but the diets of cats culled when long-haired rats were scarce were significantly more diverse than when this rodent was abundant. Rats comprised about 80 % of cats' diet by volume and frequency of occurrence when they were present, whereas birds, reptiles and invertebrates comprised the bulk of the diet when rats were not available. We conclude that, whilst feral cats are often thought to be specialist predators, they may be better considered as facultative specialists that will shift their diet in predictable ways in response to changes in the abundance of primary prey.

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Section: Cat Collection and Processingmentioning

confidence: 99%

Diet of the feral cat, Felis catus, in central Australian grassland habitats during population cycles of its principal prey

Yip

Rich²,

Dickman

2014

Mamm Res

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“…Hind-foot length and ear length are highly variable, especially on live mice. Blackwell et al (2006) also found high error rates associated with these metrics. Our field measurements on P. maniculatus in rigor mortis and primary flaccidity confirm that differences between observers may cause significant differences between measurements.…”

Section: Discussionmentioning

confidence: 79%

“…Hind-foot length and ear length had a higher proportion of residual errors and observer errors than total length and tail length. This is likely a function of the short length of hind-foot and ear measurements and greater difficulty in identifying the landmarks for these measures (Blackwell et al 2006;Martin et al 2013). Rounding errors to the nearest 0.5 mm also could have played a role in this variability, although Blackwell et al (2006) used vernier calipers to the nearest 0.1 mm and found similar error trends.…”

Section: Discussionmentioning

confidence: 99%

“…Observer measurement error may come from a number of sources including poorly or inconsistently defined metrics, lack of observer experience, plasticity in the object being measured, and the size of the object, such that smaller metrics have proportionately larger errors (Bailey and Byrnes 1990;Blackwell et al 2006). Measurement variability may also be affected by body state of the animal (Sumner 1927;Blackwell et al 2006). For instance, Blackwell et al (2006) found that measurement error was greater for live animals than for specimens that were preserved in ethanol (which results in a stiffened condition similar to rigor mortis).…”

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confidence: 99%

“…Measurement variability may also be affected by body state of the animal (Sumner 1927;Blackwell et al 2006). For instance, Blackwell et al (2006) found that measurement error was greater for live animals than for specimens that were preserved in ethanol (which results in a stiffened condition similar to rigor mortis).…”

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Dead mice can grow – variation of standard external mammal measurements from live and three postmortem body states

Stephens¹,

Karau²,

Yahnke³

et al. 2015

JMAMMAL

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The use of standard external measurements is pervasive in mammalogy, due in part to their applicability to both living and dead animals. Nevertheless, comparisons of measurements made between animals in different pre-and postmortem body states may be problematic. To investigate the impact of body state on standard measurements and their associated variances, we took 5 external measurements on 70 Mus musculus while living and in 3 postmortem body states (primary flaccidity, rigor mortis, and secondary flaccidity). Total length, tail length, and hind-foot length were significantly longer in states of primary and secondary flaccidity than when measured on live individuals or those in rigor mortis. Ear length increased from living to primary flaccidity, after which it decreased. Weight decreased between each postmortem body state, likely as an artifact of desiccation. Variance was always greater for measurements taken in the living state than during postmortem body states. Irrespective of body state, variance was particularly high for ear length and hind-foot length, which are prone to observer bias and should be used with caution. Additional tests using field-collected data from populations of Peromyscus leucopus and Peromyscus maniculatus confirmed our lab-based results from M. musculus. External measurements taken during a postmortem state should not be compared to measurements from live animals and could lead to incorrect species identification. Additionally, comparisons among individuals measured in different postmortem body states may confound efforts to assess changes in body size over space or time.

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Reconstructing climate–growth relations from the teeth of a marine mammal

et al. 2016

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Measurement Error Associated With External Measurements Commonly Used in Small-Mammal Studies

Cited by 39 publications

References 25 publications

Diet of the feral cat, Felis catus, in central Australian grassland habitats during population cycles of its principal prey

Diet of the feral cat, Felis catus, in central Australian grassland habitats during population cycles of its principal prey

Dead mice can grow – variation of standard external mammal measurements from live and three postmortem body states

Reconstructing climate–growth relations from the teeth of a marine mammal

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