Sexual Size Dimorphism and Sex Identification using Morphological Traits of Two Aegithalidae Species

Abstract

The black-throated tit, Aegithalos concinnus, and long-tailed tit, A. caudatus, are two widely-distributed species of Aegithalidae. They are thought to be monomorphic and thus difficult to differentiate between sexes in the field. We determined the sex of 296 black-throated tits and 129 long-tailed tits using DNA analysis, evaluated their sexual size dimorphism, and developed discriminant models to identify sex based on morphometries, including bill length, bill depth, bill-head length, maximum tarsus length, tarsus width, wing length, tail length, total body length, and body mass. Both species were sexually dimorphic in size, with males having larger measurements than females, except for bill length in black-throated tits, and both bill length and body mass in long-tailed tits. Moreover, both species showed similar sexual size dimorphism (SSD) among the morphological features, with tail length having the highest SSD value. The multivariate discriminant models for sex identification had an accuracy of 82% for both species, which was slightly higher than the best univariate discriminatory model for each species. Because of the complicated nature of the multivariate model, we recommend univariate models for sex identification using D = 0.491 × tail length - 24.498 (accuracy 80%) for black-throated tits and D = 0.807 × wing length - 45.934 (accuracy 78%) for long-tailed tits. Females in both species showed generally higher morphological variation than did males, resulting in lower accuracies in all discriminate functions regardless of univariate or multivariate approach. This could be the result of a sex-biased selective pressure in which males have higher selective pressures for these morphological features.

Sex-Specific Parental Care Strategies Via Nestling Age: Females Pay More Attention to Nestling Demands than Males Do in the Horned Lark,Eremophila alpestris

“…First, we performed one-sample Kolmogorov-Smirnov tests to check the normality of dataset, and found all the parameters were normally distributed (P > 0.05). To compare body sizes between the two sexes, we determined the differences in body mass and length of culmen, tarsus, wing and tail by independent-sample t tests (Li et al, 2010). To compare parental care efforts between the two sexes, we examined the differences in parental care behaviors using paired-sample t tests.…”

“…In addition, these studies also suggest that the male reduces its parental care due to uncertain paternity. Sexual size dimorphism has been widely studied in many bird spe-cies (Trivers, 1974;Berry and Shine, 1980;Li et al, 2010). However, the relationship between the parental investment and sexual size dimorphism remains unclear for monogamous and bi-parental species (Owens and Hartley, 1998;Székely et al, 2000;Palestis et al, 2012).…”

Context-dependent strategies of food allocation among offspring in a facultative cooperative breeder

“…Black-throated tits are sexually monomorphic (Li et al 2010), so the sex of adults and nestlings was determined using primers sex1'/ sex2 (Wang et al 2010) with blood samples collected through venipuncture of the brachial vein. For the two nests at which the helper and male parent could not be distinguished, we determined their identity through parentage analysis using a panel of microsatellite markers: Ase18, Ase37, Ase64, Escµ6, Man13, Pca3, PmaD22 (Simeoni et al 2007) and TG01040, TG03031, TG04004, TG04041, TG01147 (Dawson et al 2010).…”

Sex identification of the ashy-throated parrotbill (Paradoxornis alphonsianus): A species heavily hunted for bird fighting in Guizhou Province, China

“…Based on these considerations, sex determination has been intensely investigated worldwide across a variety of avian species over recent decades. [9][10][11][12][13][14][15] For bird species with conspicuous external sex-related differences in plumage (sexual dichromatism) or size (sexual dimorphism), sex identification should often be very relaxing work, particularly sex identification of adults. However, it is much more challenging to sex sexually monomorphic birds that do not display marked external sexual dimorphism.…”

“…This method has been applied to an increasing number of avian species over recent decades, for example, blacksmith lapwings (Vanellus armatus), 21 little stints (Calidris minuta), 11 black-necked grebes (Podiceps nigricollis), 12 and black-throated tits (Aegithalos concinnus). 14 The ashy-throated parrotbill (Paradoxornis alphonsianus) is a small passerine distributed in Southwest China, for which both sexes share similar plumage (Figure 1). It is a group-living species that has been observed to respond highly positively to conspecific sounds and prefers to forage and roost in shrubs and taller grass habitats during nonbreeding seasons in flocks composed of large numbers of individuals.…”