The Wilson Journal of Ornithology 123(4):720-725, 2011 
GENDER ASSIGNMENT OF WESTLAND PETRELS ( PROCELLAR1A 
WESTLANDICA) USING LINEAR DISCRIMINANT 
FUNCTION ANALYSIS 
TODD J. LANDERS, 1 * 3 - 5 TODD E. DENNIS,- AND MARK E. HAUBER 24 
R rt claSSlficadon of a s,ud y subject's gender is critical for many ecological, behavioral, and 
noctuma colonv ;• T T , dimur P hism of adu,t w ««land Petrels (Procellaria wesilandica). a large 
usin. st'lhS nNA g . , r S, " S dl *™minant function analysis and compared our results to birds classified 
UmbdT^^T S “ 5 % p en i l n7J 1 , M ,eC . C|Ue a T , hC reSU,,S rCVCa,cd a P allcr " of sexual dimorphism (Wilks' 
our s imple of Vdi.nfe , 5 ' 6 ' f thc smndard d '^nminant function analysis despite an unbalanced sex ratio in 
charac^r w/mea Id T f ^ Mlnlmum N " de P d > head length, of the seven morphometric 
characters \ve measured, successfully assigned the correct gender to 95% of all individuals sampled (n = V) Wenmvide a 
anZi^h “r„S"clTef "'7" ok ®“" * raits ««» "»> •* ««> in .he field ,n rapid,y diffc re „da, e adal ffado 
anu males O! tnts rare petrel species. Received 6 September 2010. Accepted 21 Max 20/1. 
Both cryptic and measurable sexual differences, 
including size dimorphism, are common in birds 
(Dale et al. 2007), but assignment of differences 
between females and males based on measure¬ 
ments needs to be confirmed with independent 
techniques (e.g., using anatomical or molecular 
methods) (Kahn et al. 1998, Daniel et al. 2007. 
Igic ei al. 2010). Rapid, in-hand identification of 
gender may be especially critical for behavioral 
and conservation studies, including balanced 
representation of females and males in tracking 
studtes involving expensive tagging equipment 
(e.g., Landers et al. 2011). 
The Wes,land Pelrel (Procellaria westlandica: 
Procel anidae). one of ,he larges, burrowing 
proce lan.tom, *abirds (~1.2 kg,, is endemic to 
. land. New Zealand, breeding annually during 
the austral winter ,n a number of distinct 
subcolon,es within Paparoa National Park 
and 1990, Waugh et al 
2006) This species ,s nuctumally active when at 
breed y ' USeS “ obli S ale . biparental 
breeding strategy (Brooke 2004,. Westland Pe- 
UntnZ * Z Vulnerable by ,he taternational 
20 , 0 ? ‘n C ° nservation of Nature (ILICN 
10) ’ and has been identified by the New 
lo^ NtwlZr" ThC Domain ’ A-ktand 
Auckland OffiZ^New'zcatand^' ' Stnm4 Taka P ,,,,a - 
% v tL :r r ^ 
m Con UdlnTalLVZir' W ,0 °“- 0S ^ 
todd.landcmwaucidaadcoimc.l .govt , nz 
720 
Zealand Department of Conservation as a research 
priority (Taylor 2000). 
Little is known about how male and female 
Westland Petrels differ morphologically or be- 
haviorally. which is critical for current and future 
ecological studies and conservation management 
ol this species. Westland Petrel females and males 
ate alike in having monochromatic plumage 
(Marchant and Higgins 1990). Previous studies 
of museum specimens suggested males may be 
larger (Marchant and Higgins 1990; J. A. Bartle, 
pers. comm.), but a formal assessment of the 
extent and magnitude of potential differences is 
needed. Our goal was to evaluate sexual-size 
dimorphism in Westland Petrels using discrimi¬ 
nant function analysis (Fisher 1936. Dechaume- 
Moncharmont et al. 2011). Specific objectives 
wete to: (I) evaluate if females and males could 
be reliably identified using several commonly 
measured morphometric characters. (2) identify 
which characters measured best differentiate 
temales and males, and (3) develop canonical 
classification functions to accurately and rapidly 
classify temales and males from morphological 
measurements taken in the field. 
METHODS 
l ielcl Procedures. —Thirty-seven adult West- 
land Petrels were captured from their nest burrows 
within I week, during the early breeding season in 
April 2010 at the Scotchman’s Creek colony (42 
08.8 S, 171 20.5' E). Westland. New Zealand. A 
body leather sample was collected from each bird, 
placed in a plastic bag, and sent to the Equine 
Parentage and Animal Genetic Services Centre, 
assey University, New Zealand, for commercial 
