Bird {afpt}R Documentation

Bird description


This function creates a bird description object, which is basically just a list with predefined variable names. It is named a bird object, but could also contain a description of a bat or insect. Minimal input required to construct a bird are body mass, wing span and wing area (or wing aspect ratio). Other required variables will then be given default values, or they will be estimated from allometric relations from literature.


Bird(massTotal, wingSpan, wingArea, ...)



Total mass that needs to be lifted in flight in kg


The maximum distance between the wingtips in meters


The area of the fully stretched wings including the root area (left wing, right wing and area in between the wing roots)


Any other properties of a valid bird object (see details)


This function sets up a list of properties of a bird. This definition of the bird is then used by the other functions in the package to estimate flight performance. At least three properties need to be specified: massTotal, wingSpan and wingArea. Either wingSpan or wingArea could be replaced by aspectRatio; the missing variable will then be computed. If no other properties are specified, default values will be used. Wingspan and wingarea should be measured from the maximally stretched out wing as described in Pennycuick (2008): wingspan as the maximum distance between the wingtips and wingarea as the area from a trace including the root area (where the body is).

To specify custom properties, these can simply be added as additional arguments to the function. Note that massTotal needs to be the sum of massLoad, massFat and massEmpty. The function will recompute the total mass if the specified masses are inconsistent. Allometric relations use the empty weight. Muscle mass is part of the empty mass, and as such it is represented by muscleMass as a fraction. It is used in the estimation of the mechanical power available for flight (together with the muscle properties coef.activeStrain and coef.isometricStress). The variable type is used for selected allometric relationships that are specific to that particular group. Currently, bodyFrontalArea distinguishes between 'passerine' and anything else and basalMetabolicRate distinguishes between 'passerine', 'seabird', 'bat' and anything else.

name String Common name
name.scientific Sring Scientific name
source String Source for information
massLoad Numeric Additional mass the bird is carrying (kg); 0
massFat Numeric Fat mass, i.e. fuel (kg); 0
massEmpty Numeric Empty mass, i.e. total mass - fat mass - load mass (kg)
muscleFraction Numeric Fraction [0,1] of empty mass that makes up flight muscle; 0.17*
type String Type of bird 'other'*, 'passerine'*, 'seabird', 'bat'
bodyFrontalArea Numeric Reference body frontal area used for body drag (m2)
wingbeatFrequency Numeric Typical wingbeat frequency (Hz)
coef.profileDragLiftFactor Numeric Coefficient for lift dependent profile drag; 0.03 (Klein Heerenbrinkn et al. 2015)
coef.bodyDragCoefficient Numeric Drag coefficient related to body frontal area; 0.2**
coef.conversionEfficiency Numeric Efficiency Chemical to Mechanical energy; 0.23*
coef.respirationFactor Numeric Multiplyer for metabolic overhead respiration; 1.1*
coef.activeStrain Numeric Muscle duty cycle factor; 0.26*
coef.isometricStress Numeric Maximum force produced per cross section muscle (Pa); 400000 (upper limit from Pennycuick & Rezende 1984)
basalMetabolicRate Numeric Minimum energy consumption required for sustain life functions (W) *.

* as in Flight 1.25 (Pennycuick 2008)

** Large body of data supporting higher body drag coefficients (>0.2) than in Flight 1.25 (0.1), e.g. Pennycuick et al. (1988), Hedenström & Liechti (2001), Henningsson & Hedenström (2011) and KleinHeerenbrink et al. (2016)


bird object with variables required by the various power estimating functions (e.g. computeFlappingPower).


Marco Klein Heerenbrink


Hedenström, A. & Liechti, F. (2001) Field estimates of body drag coefficient on the basis of dives in passerine birds. J. Exp. Biol. 204, 1167–75.

Henningsson, P. & Hedenström, A. (2011) Aerodynamics of gliding flight in common swifts. J. Exp. Biol. 214, 382–93. doi: 10.1242/jeb.050609

Klein Heerenbrink, M., Johansson, L. C. & Hedenström, A. (2015) Power of the wingbeat: modelling the effects of flapping wings in vertebrate flight. Proc. R. Soc. A 471. doi: 10.1098/rspa.2014.0952

KleinHeerenbrink, M., Warfvinge, K. & Hedenström, A. (2016) Wake analysis of aerodynamic components for the glide envelope of a jackdaw (Corvus monedula). J. Exp. Biol. 219, 1572–1581. doi: 10.1242/jeb.132480

Pennycuick, C. J. & Rezende, M. A. (1984) The specific power output of aerobic muscle, related to the power density of mitochondria. J. Exp. Biol., 108, 377–392.

Pennycuick, C. J., Obrecht III, H. H. & Fuller, M. R. (1988) Empirical estimates of body drag of large waterfowl and raptors. J. Exp. Biol. 135, 253–264.

Pennycuick, C. J. (2008). Modelling the flying bird. Amsterdam, The Netherlands: Elsevier.

See Also

computeAvailablePower, computeChemicalPower, computeFlappingPower, computeBodyFrontalArea, etc.


myBird = Bird(
  massTotal = 0.215,
  wingSpan = 0.67,
  wingArea = 0.0652,
  name = 'jackdaw',
  type =  'passerine'

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