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Most measurement requires the use of calipers. Here, the measurement of length, wing, tail, tarsus, and two forms of culmen measurement are shown.

Bird measurement or bird biometrics are approaches to quantify the size of birds in scientific studies. The variation in dimensions and weights across birds is one of the fundamental sources of diversity among birds, and even Within species, dimensions may vary across populations within species, between the sexes and depending on age and condition. For measurements to be useful, they must be well-defined to be consistent and comparable with those taken by others or at other points in time. Measurements can be useful to identify species, quantify functional and ecomorphological differences, study growth, variation between geographically separated forms, identify differences between the sexes, age or otherwise characterize individual birds. While certain measurements are regularly taken to study living birds, others apply only to specimens in bird collections or are measurable only in the laboratory. The conventions used for measurement can vary between authors and works, making comparisons of sizes a matter that needs considerable care.^[1]

Methods and considerations[edit]

All measurements are prone to error, both systematic and random. Measuring specific bird characteristics can further vary greatly depending on the method used. The total length of a bird is sometimes measured by putting a dead bird on its back and gently pressing the head so that the bill points to the tail tip can be measured. However, this can vary with the degree of neck stretching and cannot be measured in preserved skins in bird collections. The wing length, usually defined as the distance between the carpometacarpal joint and the most extended primary, can vary depending on whether the natural curvature of the wing is preserved or the measurement is taken on a flattened wing. The measurement can vary depending on whether a flexible tape measure is used over the curve or is measured with a rigid ruler. The definition of the length of the tail can vary when some of them have elongations, forking or other modifications.^[2]^[3] The weights of birds are even more prone to variability with their feeding and health condition and in the case of migratory species differ quite widely across seasons even for a single individual.

Despite the variations, measurements are routinely taken in taxonomic studies and the process of bird ringing. Several of the measurements are considered reliable and well-defined, at least in most birds. Although field measurements are usually univariate, laboratory techniques can often make use of multivariate measurements derived from an analysis of variation and correlations of these univariate measures. These can usually indicate variations more reliably.^[4]^[5]^[6]

Total body length[edit]

Measuring a common kestrel electrocuted on a power line

The total length of the body (also bill-to-tail length) of a bird is usually measured from dead specimens before being skinned for preservation. The measurement is made by laying the bird on its back, stretching out the neck, making the beak point forward, and measuring between the tip of the bill and the tip of the tail. However, This measurement is prone to error and is rarely used for any comparative or other scientific study.^[7]

Culmen[edit]

The upper margin of the beak or bill is referred to as Culmens the Culmen. The measurement is taken using calipers with one jaw at the tip of the upper mandible and the other at the base of the bill (at the junction with the skull, a measurement called "total culmen") or where the featherCulmeneal the Culmen (a measurement called "exposed culmen"). In the case of birds of prey, where the tip of the mandible may form a long festoon, the festoon's length may also be measured separately. In birds of prey, the measurement is usually from the bill tip to the ceres. In some birds, the distance between the back of the skull and the tip of the beak may be more suitable and less prone to variation, which results from the difficulty of interpreting the feathered base of the mandible.^[8]

Head[edit]

In some cases, measuring the distance between the back of the skull and the tip of the bill is more reliable. This measure is then termed as the head. This measurement is, however, not suitable for use with living birds that have strong neck musculature, such as cormorants.^[7]

Tarsus[edit]

The shank of the bird is usually exposed, and the length from the inner bend of the tibiotarsal articulation to the base of the toes, which is often marked by a difference in the scalation, is used as a standard measure. In most cases, the tarsus is held bent, but in some cases, the length of this bone, as visible on the outer side of the bend to the base of the toes, may be measured.

Foot[edit]

In the case of cranes and bustards, the length of the tarsus is often measured along with the length of the longest toe to the tip of the claw.^[7]

Tail[edit]

The tail is measured from the base to the tip of the longest feathers. Special structures such as racquets or streamers are measured separately. In some cases, the difference between the longest and shortest feathers, that is, the depth of the fork or notch, can also be useful.

Wing[edit]

The wing is usually measured from the carpal joint (the bend of the wing) to the tip of the longest primary feathers. The wings and feathers may often be flattened to maximize the measure. Still, in many cases, the chord length with natural curvature is preferred.^[4]^[5] In some cases the relative lengths of the longest primaries and the pattern of size variation among them can be important to measure. The wing width can also be measured from the carpal joint to the tip of the first secondary feather.^[9]

Wingspan[edit]

The wingspan is the distance between wingtips when the wings are held outstretched. This measurement is difficult to measure in the field with live birds and is prone to variation resulting from wing posture. However, the wingspan is an important dimension in bird flight studies.^[9]

Wing area[edit]

The area of a single wing can be measured manually by tracing the outline of the wing on grid paper or using a planimeter.^[10] Alternatively, the area can be obtained digitally using a photograph of the spread wing that includes a scale and then using image analysis software such as ImageJ.^[9] In bird flight aerodynamics, the area of interest is the total wing area, that is, the area of both wings plus the area of the intervening portion of the body known as the "root box".^[10] The root box is estimated from a measurement of the wing width at the base (the root chord) and the difference between the wingspan and two times the extent of a single wing.^[10] Alternatively, the total wing area can be estimated using the wingspan, wing length, and wing width and assuming simple geometric figures for the shape of the wings.^[11]

Weight[edit]

The total body weight is an important biological measurement, usually used as a proxy for body mass. However, due to its variability with seasons and body condition, it is not recommended to be used as an indicator of body size. It is, however, useful in quantifying growth in laboratory conditions and for use in clinical diagnostics as an indicator of physiological conditions. It is a fundamental quantity in bird aerodynamics.^[9] Birds in captivity are often heavier than wild specimens. Migratory birds gain weight before the migratory period but lose weight during handling or temporary captivity. Dead birds tend to weigh less than in life. The weight can vary by 5 to 10%, even during the day. The male emperor penguin loses 40% of its weight during incubation.^[12]

References[edit]

^ Baldwin, S. Prentiss; Oberholser, Harry C.; Worley, Leonard G. (1931). "Measurements of birds". Scientific Publications of the Cleveland Museum of Natural History. 2: 1–165.
^ Morgan J.H. (2004). "Remarks on the taking and recording of biometric measurements in bird ringing" (PDF). Ring. 26 (1): 71–78. doi:10.2478/v10050-008-0058-2.
^ Goodenough A.E.; Stafford R; Catlin-Groves CL; Smith A.L. & Hart A.G. (2010). "Within- and among-observer variation in measurements of animal biometrics and their influence on accurate quantification of standard biometric-based condition indices" (PDF). Ann. Zool. Fennici. 47: 323–334. doi:10.5735/086.047.0503.
^ ^a ^b Bergtold, W.H. (1925). "The Relative Value of Bird Measurements" (PDF). The Condor. 27 (2): 59–61. doi:10.2307/1363054.
^ ^a ^b Rising, J.D. & KM Somers. "The measurement of overall body size in birds" (PDF). The Auk. 106 (4): 666–674.
^ Lougheed SC, Arnold TW, Bailey RC (1991). "Measurement Error of External and skeletal variables in birds and its effect on principal components" (PDF). The Auk. 108 (2): 432–436.
^ ^a ^b ^c Rasmussen PC, Anderton JC (2005). Birds of South Asia. The Ripley Guide. Volume 2. Washington DC & Barcelona: Smithsonian Institution & Lynx Edicions. pp. 18–19.
^ Borras A, Pascual J, Senar JC. "What do different bill measures measure, and what is the best method for granivorous birds?". J. Field Ornithol. 71 (4): 606–611.
^ ^a ^b ^c ^d Claramunt, S.; Wright, N. A. (2017). "Using museum specimens to study flight and dispersal.". In Webster, M. S. (ed.). Emerging Frontiers in Collections-based Ornithological research: the Extended Specimen. Studies in Avian Biology 50. CRC Press. pp. 127–141. ISBN 9781315120454.
^ ^a ^b ^c Pennycuick, Colin J (2008). "Modelling the Flying Bird". Theoretical Ecology Series. doi:10.1016/s1875-306x(08)x0002-4. ISSN 1875-306X.
^ Fu, HY; Su, M; Chu, JJ; Margaritescu, A; Claramunt, S (2023). "New methods for estimating the total wing area of birds". Ecology and Evolution. 13 (9). doi:10.1002/ece3.10480. PMC 10474823.
^ George A. Clark, Jr. (1979). "Body Weights of Birds: A Review" (PDF). The Condor. 81 (2): 193–202. doi:10.2307/1367288.

External links[edit]

Bird Handling and Ringing Techniques including biometric measurements
SAFRING (South Africa Bird Ringing Unit) Bird Ringing manual

[1] Baldwin, S. Prentiss; Oberholser, Harry C.; Worley, Leonard G. (1931). "Measurements of birds". Scientific Publications of the Cleveland Museum of Natural History. 2: 1–165.

[2] Morgan J.H. (2004). "Remarks on the taking and recording of biometric measurements in bird ringing" (PDF). Ring. 26 (1): 71–78. doi:10.2478/v10050-008-0058-2.

[Goodenough_AE;_Stafford_R;_Catlin-Groves_CL;_Smith_AL_&_Hart_AG_2010_323–334-3] Goodenough A.E.; Stafford R; Catlin-Groves CL; Smith A.L. & Hart A.G. (2010). "Within- and among-observer variation in measurements of animal biometrics and their influence on accurate quantification of standard biometric-based condition indices" (PDF). Ann. Zool. Fennici. 47: 323–334. doi:10.5735/086.047.0503.

[Bergtold,_WH_1925_59–61-4] Bergtold, W.H. (1925). "The Relative Value of Bird Measurements" (PDF). The Condor. 27 (2): 59–61. doi:10.2307/1363054.

[Rising,_JD_&_KM_Somers_666–674-5] Rising, J.D. & KM Somers. "The measurement of overall body size in birds" (PDF). The Auk. 106 (4): 666–674.

[6] Lougheed SC, Arnold TW, Bailey RC (1991). "Measurement Error of External and skeletal variables in birds and its effect on principal components" (PDF). The Auk. 108 (2): 432–436.

[pcr-7] Rasmussen PC, Anderton JC (2005). Birds of South Asia. The Ripley Guide. Volume 2. Washington DC & Barcelona: Smithsonian Institution & Lynx Edicions. pp. 18–19.

[8] Borras A, Pascual J, Senar JC. "What do different bill measures measure, and what is the best method for granivorous birds?". J. Field Ornithol. 71 (4): 606–611.

[ClaramuntWright-9] Claramunt, S.; Wright, N. A. (2017). "Using museum specimens to study flight and dispersal.". In Webster, M. S. (ed.). Emerging Frontiers in Collections-based Ornithological research: the Extended Specimen. Studies in Avian Biology 50. CRC Press. pp. 127–141. ISBN 9781315120454.

[:0-10] Pennycuick, Colin J (2008). "Modelling the Flying Bird". Theoretical Ecology Series. doi:10.1016/s1875-306x(08)x0002-4. ISSN 1875-306X.

[11] Fu, HY; Su, M; Chu, JJ; Margaritescu, A; Claramunt, S (2023). "New methods for estimating the total wing area of birds". Ecology and Evolution. 13 (9). doi:10.1002/ece3.10480. PMC 10474823.

[12] George A. Clark, Jr. (1979). "Body Weights of Birds: A Review" (PDF). The Condor. 81 (2): 193–202. doi:10.2307/1367288.

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+{{Short description|Bird biometrics}}
-[[File:BirdMorphometrics.jpg|thumb|Most measurement requires the use of [[calipers]]. Here the measurement of length, wing, tail, tarsus and two forms of culmen measurement are shown.]]
+[[File:BirdMorphometrics.jpg|thumb|Most measurement requires the use of [[calipers]]. Here, the measurement of length, wing, tail, tarsus, and two forms of culmen measurement are shown.]]
-'''Bird measurement''' or '''bird biometrics''' are approaches to quantify the [[size]] of [[bird]]s in scientific studies. The measurements of the [[length]]s of specific parts and the [[weight]]s of birds varies between species, populations [[Intraspecific variability|within species]], between the sexes and depending on [[Biomarkers of aging|age]] and condition. In order for measurements to be useful, they need to be well defined so that measurements taken are consistent and comparable with those taken by others or at other points of time. Measurements can be useful to study growth, variation between geographically separated forms, identify [[Sexual dimorphism measures|differences between the sexes]], age or otherwise characterize individuals birds. While certain measurements are regularly taken in the field to study living birds some others are applicable only to specimens in the [[Natural history museum|museum]] or measurable only in a laboratory. The conventions used for measurement can vary widely between authors and works, making comparisons of sizes a matter that needs considerable care.<ref>{{cite journal |title=Measurements of birds|last1=Baldwin| first1=S. Prentiss| first2=Harry C.| last2=Oberholser |first3=Leonard G.| last3=Worley | year=1931 | journal=Scientific Publications of the Cleveland Museum of Natural History| volume=2 |pages=[https://archive.org/details/measurementsofbi00bald/page/n22 1]–165 |url=https://archive.org/details/measurementsofbi00bald}}</ref>
+'''Bird measurement''' or '''bird biometrics''' are approaches to quantify the [[size]] of [[bird]]s in scientific studies. The variation in dimensions and [[weight]]s across birds is one of the fundamental sources of diversity among birds, and even Within species, dimensions may vary across populations [[Intraspecific variability|within species]], between the sexes and depending on [[Biomarkers of aging|age]] and condition. For measurements to be useful, they must be well-defined to be consistent and comparable with those taken by others or at other points in time. Measurements can be useful to identify species, quantify functional and [[ecomorphology|ecomorphological]] differences, study growth, variation between geographically separated forms, identify [[Sexual dimorphism measures|differences between the sexes]], age or otherwise characterize individual birds. While certain measurements are regularly taken to study living birds, others apply only to specimens in [[bird collections]] or are measurable only in the laboratory. The conventions used for measurement can vary between authors and works, making comparisons of sizes a matter that needs considerable care.<ref>{{cite journal |title=Measurements of birds|last1=Baldwin| first1=S. Prentiss| first2=Harry C.| last2=Oberholser |first3=Leonard G.| last3=Worley | year=1931 | journal=Scientific Publications of the Cleveland Museum of Natural History| volume=2 |pages=[https://archive.org/details/measurementsofbi00bald/page/n22 1]–165 |url=https://archive.org/details/measurementsofbi00bald}}</ref>
 ==Methods and considerations==
-All measurement is prone to [[observational error|error]], both systematic and random. The measurement of certain bird characteristics can further [[measurement uncertainty|vary]] greatly depending on the method used. The total length of a bird is sometimes measured by putting a dead bird on its back and gently pressing the head so that the bill point to the tail tip can be measured. This can however vary with the handling and can depend on the age and state of shrinkage in the case of measurements taken from preserved skins in [[bird collections]]. The wing length usually defined as the distance between the bend of the wing and the longest primary can also vary widely in some large birds which have a curved wing surface as well as curved primaries. The measurement can additionally vary depending on whether a [[tape measure|flexible tape]] measure is used over the curve or if measured with a rigid ruler. The definition of the length of the tail can vary when some of them have elongations, forking or other modifications.<ref>{{cite journal|author=Morgan J.H. |year=2004| title=Remarks on the taking and recording of biometric measurements in bird ringing |journal=Ring|volume=26|issue=1|pages=71–78 |url=http://thering.ug.edu.pl/pdf/26-1/morgan.pdf |doi=10.2478/v10050-008-0058-2}}</ref><ref name="Goodenough AE; Stafford R; Catlin-Groves CL; Smith AL & Hart AG 2010 323–334">{{cite journal|author1=Goodenough AE |author2=Stafford R |author3=Catlin-Groves CL |author4=Smith AL |author5=Hart AG |lastauthoramp=yes |year=2010|title=Within- and among-observer variation in measurements of animal biometrics and their influence on accurate quantification of common biometric-based condition indices|journal=Ann. Zool. Fennici|volume=47| pages=323–334|url=http://www.sekj.org/PDF/anz47-free/anz47-323.pdf|doi=10.5735/086.047.0503}}</ref><ref name="Goodenough AE; Stafford R; Catlin-Groves CL; Smith AL & Hart AG 2010 323–334"/> The weights of birds are even more prone to variability with their feeding and health condition and in the case of [[Bird migration|migratory species]] differ quite widely across seasons even for a single individual.
+All measurements are prone to [[observational error|error]], both systematic and random. Measuring specific bird characteristics can further [[measurement uncertainty|vary]] greatly depending on the method used. The total length of a bird is sometimes measured by putting a dead bird on its back and gently pressing the head so that the bill points to the tail tip can be measured. However, this can vary with the degree of neck stretching and cannot be measured in preserved skins in [[bird collections]]. The wing length, usually defined as the distance between the [[carpometacarpal joint]] and the most extended primary, can vary depending on whether the natural curvature of the wing is preserved or the measurement is taken on a flattened wing. The measurement can vary depending on whether a [[tape measure|flexible tape]] measure is used over the curve or is measured with a rigid ruler. The definition of the length of the tail can vary when some of them have elongations, forking or other modifications.<ref>{{cite journal|author=Morgan J.H. |year=2004| title=Remarks on the taking and recording of biometric measurements in bird ringing |journal=Ring|volume=26|issue=1|pages=71–78 |url=http://thering.ug.edu.pl/pdf/26-1/morgan.pdf |doi=10.2478/v10050-008-0058-2}}</ref><ref name="Goodenough AE; Stafford R; Catlin-Groves CL; Smith AL & Hart AG 2010 323–334">{{cite journal|author1=Goodenough A.E. |author2=Stafford R |author3=Catlin-Groves CL |author4=Smith A.L. |author5=Hart A.G. |name-list-style=amp |year=2010|title=Within- and among-observer variation in measurements of animal biometrics and their influence on accurate quantification of standard biometric-based condition indices|journal=Ann. Zool. Fennici|volume=47| pages=323–334|url=http://www.sekj.org/PDF/anz47-free/anz47-323.pdf|doi=10.5735/086.047.0503}}</ref> The weights of birds are even more prone to variability with their feeding and health condition and in the case of [[Bird migration|migratory species]] differ quite widely across seasons even for a single individual.
-Despite the variations, measurements are routinely taken in the process of [[bird ringing]] and for other studies. Several of the measurements are considered quite constant and well defined, at least in the vast majority of birds. Although field measurements are usually [[univariate]], laboratory techniques can often make use of multivariate measurements derived from an [[Multivariate statistics|analysis of variation]] and correlations of these univariate measures. These can often indicate variations more reliably.<ref name="Bergtold, WH 1925 59–61">{{cite journal|url=http://sora.unm.edu/sites/default/files/journals/condor/v027n02/p0059-p0061.pdf |title=The Relative Value of Bird Measurements|author=Bergtold, WH|year=1925| pages=59–61| volume=27| issue=2| doi=10.2307/1363054| journal=The Condor}}</ref><ref name="Rising, JD & KM Somers 666–674">{{cite journal|url=http://sora.unm.edu/sites/default/files/journals/auk/v106n04/p0666-p0674.pdf |title=The measurement of overall body size in birds|author1=Rising, JD  |author2=KM Somers |lastauthoramp=yes |journal=The Auk|volume=106| issue=4|pages=666–674}}</ref><ref>{{cite journal| title=Measurement Error of External and skeletal variables in birds and its effect on principal components|vauthors=Lougheed SC, Arnold TW, Bailey RC |url=http://sora.unm.edu/sites/default/files/journals/auk/v108n02/p0432-p0436.pdf|volume=108| issue=2| pages=432–436| year=1991}}</ref>
+Despite the variations, measurements are routinely taken in [[taxonomy|taxonomic]] studies and the process of [[bird ringing]]. Several of the measurements are considered reliable and well-defined, at least in most birds. Although field measurements are usually [[univariate]], laboratory techniques can often make use of multivariate measurements derived from an [[Multivariate statistics|analysis of variation]] and correlations of these univariate measures. These can usually indicate variations more reliably.<ref name="Bergtold, WH 1925 59–61">{{cite journal|url=http://sora.unm.edu/sites/default/files/journals/condor/v027n02/p0059-p0061.pdf |title=The Relative Value of Bird Measurements|author=Bergtold, W.H. |year=1925| pages=59–61| volume=27| issue=2| doi=10.2307/1363054| journal=The Condor}}</ref><ref name="Rising, JD & KM Somers 666–674">{{cite journal|url=http://sora.unm.edu/sites/default/files/journals/auk/v106n04/p0666-p0674.pdf |title=The measurement of overall body size in birds|author1=Rising, J.D. |author2=KM Somers |name-list-style=amp |journal=The Auk|volume=106| issue=4|pages=666–674}}</ref><ref>{{cite journal| title=Measurement Error of External and skeletal variables in birds and its effect on principal components|vauthors=Lougheed SC, Arnold TW, Bailey RC |url=http://sora.unm.edu/sites/default/files/journals/auk/v108n02/p0432-p0436.pdf |journal=The Auk |volume=108| issue=2| pages=432–436| year=1991}}</ref>
+==Total body length==
-==Length==
+[[File:Pustelga lep.jpg|thumb|Measuring a [[common kestrel]] electrocuted on a power line]]
-The length of a bird is usually measured from dead specimens prior to their being skinned for preservation. The measurement is made by laying the bird on its back and flattening out the head and neck gently and measuring between the tip of the bill and the tip of the tail. This measurement is however extremely prone to error and is rarely ever used for any comparative or other scientific study.<ref name=pcr/>
+The total length of the body (also bill-to-tail length) of a bird is usually measured from dead specimens before being skinned for preservation. The measurement is made by laying the bird on its back, stretching out the neck, making the beak point forward, and measuring between the tip of the bill and the tip of the tail. However, This measurement is prone to error and is rarely used for any comparative or other scientific study.<ref name=pcr/>
 ==Culmen==
 [[File:MeasureBeakThrush.jpg|thumb|Measuring the culmen]]
-The upper margin of the beak or bill is referred to as the culmen and the measurement is taken using calipers with one jaw at the tip of the upper mandible and the other at base of the skull or the first feathers depending on the standard chosen. In the case of birds of prey where the tip of the mandible may form a long festoon, the length of the festoon may be measured separately as well. In birds of prey the measurement is usually from the bill tip to the ceres. In some birds the distance between the back of the skull and the tip of the beak may be more suitable and less prone to variation resulting from the difficulty of interpreting the feathered base of the mandible.<ref>{{cite journal|volume=71| issue=4| pages=606–611| title=What do different bill measures measure and what is the best method to use in granivorous birds?|vauthors=Borras A, Pascual J, Senar JC |journal=J. Field Ornithol.|url=http://www.bcn.es/museuciencies_fitxers/imatges/FitxerContingut1987.pdf}}</ref>
+The upper margin of the beak or bill is referred to as Culmens the [[Culmen (bird)| Culmen]]. The measurement is taken using calipers with one jaw at the tip of the upper mandible and the other at the base of the bill (at the junction with the skull, a measurement called "total culmen") or where the featherCulmeneal the Culmen (a measurement called "exposed culmen"). In the case of birds of prey, where the tip of the mandible may form a long festoon, the festoon's length may also be measured separately. In birds of prey, the measurement is usually from the bill tip to the ceres. In some birds, the distance between the back of the skull and the tip of the beak may be more suitable and less prone to variation, which results from the difficulty of interpreting the feathered base of the mandible.<ref>{{cite journal|volume=71|issue=4|pages=606–611|title=What do different bill measures measure, and what is the best method for granivorous birds?|vauthors=Borras A, Pascual J, Senar JC|journal=J. Field Ornithol.}}</ref>
 ==Head==
-In some cases it is more reliable to measure the distance between the back of the skull and the tip of the bill. This measure is then termed as the head. This measurement is however not suitable for use with living birds that have strong neck musculature such as the cormorants.<ref name=pcr/>
+In some cases, measuring the distance between the back of the skull and the tip of the bill is more reliable. This measure is then termed as the head. This measurement is, however, not suitable for use with living birds that have strong neck musculature, such as cormorants.<ref name=pcr/>
 ==Tarsus==
+[[file:BirdMorphometrics_(tarsus_measurement).jpg|thumb|140px|Tarsus]]
-The shank of the bird is usually exposed and the length from the inner bend of the tibiotarsal articulation to the base of the toes which is often marked by a difference in the scalation is used as a standard measure. In most cases the tarsus is held bent but in some cases the measurement may be made of the length of this bone as visible on the outer side of the bend to the base of the toes.
+The [[Tarsometatarsus|shank]] of the bird is usually exposed, and the length from the inner bend of the tibiotarsal articulation to the base of the toes, which is often marked by a difference in the scalation, is used as a standard measure. In most cases, the tarsus is held bent, but in some cases, the length of this bone, as visible on the outer side of the bend to the base of the toes, may be measured.
 ==Foot==
-In the case of [[Crane (bird)|cranes]] and [[bustard]]s, the length of the tarsus is often measured along with the length of the longest toe to the tip of the claw.<ref name=pcr>{{cite book|vauthors=Rasmussen PC, Anderton JC|lastauthoramp=yes |year=2005| title=Birds of South Asia. The Ripley Guide. Volume 2|pages=18–19|publisher=Smithsonian Institution & Lynx Edicions|place=Washington DC & Barcelona}}</ref>
+In the case of [[Crane (bird)|cranes]] and [[bustard]]s, the length of the tarsus is often measured along with the length of the longest toe to the tip of the claw.<ref name=pcr>{{cite book|vauthors=Rasmussen PC, Anderton JC |year=2005| title=Birds of South Asia. The Ripley Guide. Volume 2|pages=18–19|publisher=Smithsonian Institution & Lynx Edicions|place=Washington DC & Barcelona}}</ref>
 ==Tail==
-The measurement of the tail is taken from the base of the tail to the tip of the longest feathers. In the case where special structures such as racquets or streamers exist, these are separately measured. In some cases the difference between the longest and shortest feathers, that is the depth of the fork or notch can also be of use.
+The tail is measured from the base to the tip of the longest feathers. Special structures such as racquets or streamers are measured separately. In some cases, the difference between the longest and shortest feathers, that is, the depth of the fork or notch, can also be useful.
 ==Wing==
 [[File:MeasureWingThrush.jpg|thumb|Measuring the wing]]
-The wing is usually measured from the bend of the wing to the tip of the longest primary feathers. Often the wings and feathers may be flattened so that the measure is maximized but in some cases the chord length with natural curvature is preferred.<ref name="Bergtold, WH 1925 59–61"/><ref name="Rising, JD & KM Somers 666–674"/> In some cases the relative lengths of the longest primaries and the pattern of size variation among them can be important to measure.
+The wing is usually measured from the carpal joint (the bend of the wing) to the tip of the longest primary feathers. The wings and feathers may often be flattened to maximize the measure. Still, in many cases, the [[Wing chord (biology)|chord length]] with natural curvature is preferred.<ref name="Bergtold, WH 1925 59–61"/><ref name="Rising, JD & KM Somers 666–674"/> In some cases the relative lengths of the longest primaries and the pattern of size variation among them can be important to measure. The wing width can also be measured from the carpal joint to the tip of the first secondary feather.<ref name=ClaramuntWright>{{cite book |last1= Claramunt |first1=S.|last2= Wright |first2=N. A. |date=2017 |editor-last= Webster |editor-first= M. S. |title=Emerging Frontiers in Collections-based Ornithological research: the Extended Specimen. Studies in Avian Biology 50 |publisher=CRC Press |pages=127–141 |chapter=Using museum specimens to study flight and dispersal. |isbn= 9781315120454}}</ref>
 ==Wingspan==
-Wingspan is the distance between wingtips when the wings are held outstretched. This is particularly prone to variation resulting from wing posture and is rarely used except as a rough indicator of size. Additionally, this cannot be easily and reliably measured in the field with living birds.
+The wingspan is the distance between wingtips when the wings are held outstretched. This measurement is difficult to measure in the field with live birds and is prone to variation resulting from wing posture. However, the wingspan is an important dimension in [[bird flight]] studies.<ref name=ClaramuntWright/>
+==Wing area==
+The area of a single wing can be measured manually by tracing the outline of the wing on grid paper or using a [[planimeter]].<ref name=":0">{{Cite journal |last=Pennycuick |first=Colin J |date=2008 |title=Modelling the Flying Bird |url=http://dx.doi.org/10.1016/s1875-306x(08)x0002-4 |journal=Theoretical Ecology Series |doi=10.1016/s1875-306x(08)x0002-4 |issn=1875-306X}}</ref> Alternatively, the area can be obtained digitally using a photograph of the spread wing that includes a scale and then using image analysis software such as [[ImageJ]].<ref name="ClaramuntWright" /> In [[Bird flight|bird flight aerodynamics]], the area of interest is the total wing area, that is, the area of both wings plus the area of the intervening portion of the body known as the "root box".<ref name=":0" /> The root box is estimated from a measurement of the wing width at the base (the [[Chord (aeronautics)|root chord]]) and the difference between the wingspan and two times the extent of a single wing.<ref name=":0" /> Alternatively, the total wing area can be estimated using the wingspan, wing length, and wing width and assuming simple geometric figures for the shape of the wings.<ref>{{Cite journal |last=Fu |first=HY |last2=Su |first2=M |last3=Chu |first3=JJ |last4=Margaritescu |first4=A |last5=Claramunt |first5=S |date=2023 |title=New methods for estimating the total wing area of birds |url=https://onlinelibrary.wiley.com/doi/10.1002/ece3.10480 |journal=Ecology and Evolution |language=en |volume=13 |issue=9 |doi=10.1002/ece3.10480 |issn= |pmc=10474823 |pmid=|doi-access=free }}</ref>
 ==Weight==
-The weights of birds are notoriously variable and cannot be used as indication of size. They are however useful in quantifying growth in laboratory conditions and for use in clinical diagnostics as an indicator of physiological condition. Birds in captivity are often heavier than wild specimens. Migratory birds gain weight prior to the migratory period but lose weight during handling or temporary captivity. Dead birds tend to weigh less than in life. Even during the course of a day, the weight can vary by 5 to 10%. The male [[emperor penguin]] loses 40% of its weight during the course of incubation.<ref>{{Cite journal|title=Body Weights of Birds: A Review|author=George A. Clark, Jr.|journal=The Condor |volume=81| issue= 2| year=1979| pages=193–202| url= http://sora.unm.edu/sites/default/files/journals/condor/v081n02/p0193-p0202.pdf|doi=10.2307/1367288}}</ref>
+The total body weight is an important biological measurement, usually used as a proxy for body [[mass]]. However, due to its variability with seasons and body condition, it is not recommended to be used as an indicator of body size. It is, however, useful in quantifying growth in laboratory conditions and for use in clinical diagnostics as an indicator of physiological conditions. It is a fundamental quantity in bird [[aerodynamics]].<ref name=ClaramuntWright/> Birds in captivity are often heavier than wild specimens. Migratory birds gain weight before the migratory period but lose weight during handling or temporary captivity. Dead birds tend to weigh less than in life. The weight can vary by 5 to 10%, even during the day. The male [[emperor penguin]] loses 40% of its weight during incubation.<ref>{{Cite journal|title=Body Weights of Birds: A Review|author=George A. Clark, Jr.|journal=The Condor |volume=81| issue= 2| year=1979| pages=193–202| url= http://sora.unm.edu/sites/default/files/journals/condor/v081n02/p0193-p0202.pdf|doi=10.2307/1367288}}</ref>
 ==References==
@@ Line 40: / Line 46: @@
 ==External links ==
-* [ftp://ftp.fao.org/docrep/fao/010/a1521e/a1521e04.pdf Measuring birds]{{Dead link|date=July 2020 |bot=InternetArchiveBot |fix-attempted=yes }}
+* [http://www.fao.org/3/a1521e/a1521e04.pdf Bird Handling and Ringing Techniques] including biometric measurements
 * [https://web.archive.org/web/20171019032817/http://safring.adu.org.za/downloads/ringers-manual.pdf SAFRING (South Africa Bird Ringing Unit) Bird Ringing manual]