The use of head and bill length to sex live gulls Laridae

Sex determination of Iberian Azure‐winged MagpiesCyanopica cyanus cookiby discriminant analysis of external measurements

“…Our results may support this hypothesis, since size dimorphism is present from an early age and first-year birds are able to breed in their first year (Radford & du Plessis 2004). Though head+bill length has not been used regularly in ornithology, this measure may be very useful in distinguishing between the sexes of other bird species, since it can be measured with a high degree of consistency (Coulson et al 1983, Hanners & Patton 1985, Clark et al 1991, Franeker & ter Braak 1993, Shephard et al 2004. Tail length may also be useful in sexing corvids, since most have a long tail that is prominently displayed in both inter-and intra-sexual contexts by flicking the tail into an exaggeratedly upright position (Coombs 1978;pers obs).…”

“…Many bird species, however, are not obviously dimorphic in size or plumage, so field identification of males and females is difficult. In such cases, individuals may be sexed by breeding behaviour (Baeyens 1981) or by the presence of a brood patch on incubating females (Green 1982, Reese & Kadlec 1982, but this is possible only for sexually active individuals during the breeding season (Coulson et al 1983). When sex determination in the field is impossible, alternative methods include genetic analysis (Griffiths et al 1998), hormone analysis (Eason et al 2001) and laparoscopy (Risser 1971); however, these techniques are expensive, time-consuming, highly invasive, and require trained researchers and specialised equipment (Edgington 1989).…”

Sexing Black‐legged Kittiwakes by measurement

“…This was measured using a scale with a 10x10-cm stop plate fixed to one end of a rule and a similar plate that slid over the rule (see illustration in Coulson et al 1983). The tip of the beak and the back of the head were placed against the plates and the length read from the rule.…”

“…However, this method involves more time and effort because several different measurements are required on each individual, something which may be undesirable if a large catch is made at one time eg by cannon netting. Furthermore, Coulson et al (1983) showed that for gulls, only minimal advantage was obtained by using a combination of measures over a single measure, and even when using several measurements, individuals were still not all sexed with certainty.…”

Interregional Breeding Dispersal of Adult Roseate Terns

“…Coulson et al 1983;Chardine and Morris 1989;Craik 1999;Fletcher and Hamer 2003;Devlin et al 2004;Bluso et al 2006;Nisbet et al 2007;Shealer and Cleary 2007;Herring et al 2010), we found head length to be the most reliable trait for sexing birds in the hand. Although mean head lengths of males and females differed by only 3.2 mm (approximately a 4% difference), there was less overlap between the sexes in this than in other measurements (Table 1).…”