Intraspecific Variation in Loggerhead Shrikes: Sexual Dimorphism and Implication for Subspecies Classification

Biometrics of the Southern Grey ShrikeLanius meridionalisin relation to age and sex

“…Several of the biometric results from this study are similar to analyses of the Loggerhead Shrike (Slack 1994, Collister & Wicklum 1996, including the difference in wing, tail and bill between sex and age classes, the greater extent of white on the wing and tail of males and the large overlap in size measurements. This suggests that, at least in terms of biometry, the Southern Grey Shrike is more similar to the Loggerhead Shrike than to the Great Grey Shrike.…”

“…We also measured the extent of white on the primaries (WP, from distal edge of basal white area to wrist) and on the rectrices (WR, greatest length of white spot on inner web of the distal end of outer rectrix) (Fig 1) with a 0.5 mm precision ruler as described by Collister & Wicklum (1996). In each shrike, both WP and WR were measured three times and the final value used for analysis was the average of these three measurements.…”

“…Not all measurements were taken on all birds and, therefore, the sample size varied. Weight was not considered in the analysis since it can vary substantially during the breeding period (Collister & Wicklum 1996, Takagi 1996, but the average value is reported.…”

Sexual size dimorphism and positive assortative mating in red-backed shrike Lanius collurio: an adaptive value?

“…This is consistent with previous reports for this and other shrike species (Collister and Wicklum 1996;Takagi 1996;Ku niak and Tryjanowski 2003; but see Tryjanowski and Yosef 2002 for migratory red-¢ z Table 1. Differences in body measurements between the sexes for red-backed shrikes Lanius collurio.…”

Sexing adult Northern Shrikes using DNA, morphometrics, and plumage

“…Although wing and tail lengths overlapped considerably between the sexes (about 15–20% of individuals sampled), males generally had longer wing chords and longer tails with less black on R6 than females. Similar biometric results have been observed in Southern Grey Shrikes ( L. meriodionalis ; Gutierrez‐Corchero et al 2007) and Loggerhead Shrikes ( L. ludovicianus ; Slack 1994, Collister and Wicklum 1996), but Cramp and Perrins (1993) found no sexual differences in wing or tail lengths among study skins of Northern Shrikes in The Netherlands. In our study, the discriminant function with these two metric variables correctly classified over 85% of adult Northern Shrikes and, when combined with divergent plumage features, provided an accurate means of sex determination.…”