Effects of Size, Condition, Measurer, and Time on Measurements of Snakes

Cundall, David; Deufel, Alexandra; MacGregor, Gylla; Pattishall, Abigail; Richter, Martin L.

doi:10.1655/herpetologica-d-16-00006.1

Cited by 17 publications

(12 citation statements)

References 22 publications

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“…For simplicity, we recommend that brown treesnake body length predictions can be made from head length measurements (HL + HL 2 ) alone (Table S1). Although these values are predicted to 1 mm precision, Cundall et al (2016) caution that the flexibility of anatomical elements of snakes and inherent imprecision in measurements within and among measurers and under varying specimen conditions (preserved, anesthetized, unanesthetized) indicate that there (A) (B)…”

Section: Discussionmentioning

confidence: 90%

“…Head length alone is a relatively precise predictor of brown treesnake length, explaining 95.9% of the variation in SVL after removing outlier measurements. Given the challenge of measuring a prehensile and uncooperative snake over a flexible tape, and interobserver differences in the force with which snakes are stretched (Penning et al 2013, Cundall et al 2016, much of the remaining 4.1% of unexplained variation could be due to error in SVL measurement. It may be that brown treesnake head length is a more precise predictor of body length than direct measurement of SVL with a flexible tape, given the less difficult task of measuring a relatively small, rigid, and easily restrained part of the anatomy with calipers.…”

Section: Discussionmentioning

confidence: 99%

“…Measurement of HL is limited primarily to one rigid bone assembly (lower mandible) and how it articulates with the premaxillary (snout). In comparison, HW may be more prone to observer error (Cundall et al 2016), given the less precise landmarks for measurement and the potential for improper inclusion of both lower mandibles in measurements, as they are laterally mobile. Head width has also been reported as a poor predictor of other allometric relationships in snakes such as gape size (Hampton 2014).…”

Section: Discussionmentioning

confidence: 99%

“…We measured snout-vent length (SVL, mm) by gently stretching the body of the snake along a flexible tape as muscle contractions relaxed; this has been the standard method for brown treesnake body length measurements, having been conducted tens of thousands of times including on individuals that are repeatedly measured with no apparent ill effect. Although length measurements from unanesthetized snakes are less precise than those from anesthetized or preserved specimens (Cundall et al 2016), stretching along a tape without anesthesia is typically the only practical method for field studies using free-ranging snakes. We measured body mass (g) with hanging spring scales (Pesola Präzisionswaagen AG, Schindellegi, Switzerland) or electronic balances, in increments of 1 to 10 g, depending on the range and precision of the scale and mass of the snake.…”

Section: Methods Specimen Collection and Measurementmentioning

confidence: 99%

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Allometric Regression of Snake Body Length from Head Image Measurements

Siers

2021

Wildlife Society Bulletin

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As in many fields of wildlife research and management, camera devices and photogrammetry have become an integral part of the toolkit for exploring otherwise-unseen aspects of the biology, behavior, and control of the invasive brown treesnake (Boiga irregularis) on Guam. Because brown treesnakes are cryptic and nocturnal, and nearly all aspects of their ecology are influenced by snake size, methods are needed to estimate snake size from images captured by infrared wildlife cameras. Unfortunately, it is difficult to capture images of an entire snake's length at a controlled distance from a simple camera setup. Here, I describe the allometric relationships between brown treesnake body length and potential predictors: head measurements, sex, and body condition. Head length (HL) was the most important predictor of body length, alone accounting for 95.9% of the variation in brown treesnake snout-vent length (SVL). We provide simple regression equations for predicting brown treesnake length from head measurements, an example of how to extract measurements from images, and a convenient lookup table for predicting SVL and 80% prediction intervals from HL alone. Coupled with a simple camera setup that controls subject distance and includes size standards in the image, we can estimate brown treesnake body size from images that include only the head when photographed from above. These methods have been developed to enable ongoing assessments of brown treesnake predation risk following landscape-scale suppression efforts that could enable the reintroduction of extirpated native wildlife.

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Section: Discussionmentioning

confidence: 90%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methods Specimen Collection and Measurementmentioning

confidence: 99%

See 2 more Smart Citations

Allometric Regression of Snake Body Length from Head Image Measurements

Siers

2021

Wildlife Society Bulletin

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“…Of course we cannot estimate divergence times to that sort of precision, but this is similar to what we do when we claim to pinpoint the locality of a lizard to the nearest 1 mm. In fact, we cannot even measure the snake's length to such a degree of precision: Cundall et al (2016) actually claimed that snakes "have no exact size". But it is easy to forget this when we use a device that offers us an illusion of greater precision.…”

Section: Decimal Placesmentioning

confidence: 99%

The smartphone fallacy – when spatial data are reported at spatial scales finer than the organisms themselves

Meiri¹

2018

Frontiers of Biogeography

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Thankfully, the days when specimen localities could be described in extremely vague terms such as "Peru" or "Indochina" are long gone. But the pendulum has swung too far the other way. Latitude and longitude data of specimens and study areas (such as small nature reserves) are nowadays commonly reported to the 0.000001 of a degree (or 0.01 of a second) or even more "precisely". This is done either because of converting across measurement systems or because hand-held devices and internet sources provide this kind of precision. We probably report this degree of precision because we are reluctant to round-feeling it would make the data better and more "scientific". I point out the scale referred to by different degrees of geographic precision (e.g., ~10cm for 6 decimal places) and argue that such degree of precision is false for two reasons: first, it is finer than actually achievable by hand held devices such as smartphones and GPS receivers (and much finer than we can tell from a map). Second, for large animals, such precision can refer to one part of the organism, and not another. I urge scientists to use simple reality checks when reporting latitude and longitude data and report precision at meaningful scales.

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How anatomy influences measurements of snakes

Cundall,

Deufel,

Pattishall

2024

Journal of Morphology

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Anatomy compromises the precision and accuracy of measurements made of the body length and head size of live snakes. Body measures (snout‐vent length, SVL) incorporate many synovial intervertebral joints, each allowing flexion and limited extension and compression. Radiographs of the trunk in 14 phylogenetically diverse species in resting and stretched conditions combined with dissections and histological analysis of intervertebral joints show that the synovial nature of these joints underlies the variance in SVL measures. Similarly, the ubiquity and variety of viscoelastic tissues connecting mobile snout and jaw elements of alethinophidian snakes underlie variances in length and width measures of the head. For the overall size of the head and jaw apparatus, the part that can be most easily and relatively precisely measured for many snakes is the mandible because it has only one mobile joint. As to accuracy, the anatomy of intervertebral and cranial joints supports the hypothesis that in living snakes, the head and trunk have no exact size.

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Effects of Size, Condition, Measurer, and Time on Measurements of Snakes

Cited by 17 publications

References 22 publications

Allometric Regression of Snake Body Length from Head Image Measurements

Allometric Regression of Snake Body Length from Head Image Measurements

The smartphone fallacy – when spatial data are reported at spatial scales finer than the organisms themselves

How anatomy influences measurements of snakes

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