Data from: In situ measurements of animal morphological features; a non-invasive method

1) Measurements of morphological features are important for ecological
studies, especially on free-ranging wild animal species. Conventionally,
specimens either dead or in captivity are used for morphometric studies,
which is difficult in the case of wild species for several reasons.
Capturing would be even futile when research questions are relating to
issues such as prey size selection or estimation of intake rate in under
field conditions, where in situ morphometric measurements are inevitable.
Remotely estimating morphometric features via, avian bill and head length
are always laden with wide variances. Hence, we developed this technique
for in situ measurements of animal morphology through digital photographs.
2) This non-invasive novel method for in situ estimation of individuals’
morphometric measurements uses digital photographs' metadata. We
extracted the metadata (field of view, focal length, subject-distance
etc.,) in Exchangeable Image File Format (EXIF) from digital images using
freely available software, and the unknown sizes were estimated from each
image. Cardboard (fish) models were, at first, used to estimate the
accuracy of measurements comparing actual and estimated values, and the
same protocol was repeated on museum specimens (bird). Finally, we checked
the repeatability of this method under field conditions using free ranging
Chickens (Gallus gallus domesticus). The results under different
conditions were subjected to rigorous statistical testing. 3) Upon
comparing the actual with estimated values, obtained from three distinct
types of objects (1. Cardboard model, 2. Museum specimens, and 3. Live
birds under field conditions), variations were found non-significant
affirming the assumption that actual value (Y) = estimated value (X) with
inconsequential variance of the Y from X. Moreover, both the relative and
absolute errors between the actual and estimated values were so low,
indicating that this method yielded neither over-estimation nor
under-estimation. 4) The advantage of this non-invasive method is that it
could generate reasonably accurate morphometric measurements at a
relatively low cost for routine morphometric works in field conditions. We
envisage significant utility of this non-invasive technique in different
fields of science such as biology, morphology, ecology, evolution,
wildlife, conservation science, agriculture, forensics and engineering
design.