TDK conference 2017

In birds sex identification can be problematic on field, especially in case of sexually plumage-monomorphic species. We can get precise results by taking DNA samples for molecular sex determination, but in many cases these methods can be destructive or invasive. Furthermore this procedure is time- and money consuming. In species where it is possible, better solution could be for sex identification to introduce a protocol based on statistical methods and morphological variables. The eastern imperial eagle (Aquila heliaca) is considered a strictly protected species in Hungary. In this species we cannot observe any difference in plumage coloration between genders, but sexual dimorphism appears in body size, even the nestling females are larger than males.

The whole Hungarian breeding population is monitored by different species protection programs(*). DNA samples are taken from chicks during ringing, in form of armpit feathers, and different body size variables are measured, such as hind claw length (mm), tarsus diameter (mm), tarsus length (mm), tail length (mm) and body mass (g). Furthermore development stages of the chicks are estimated based on the colour of plumage which is determined by the ratio of down feathers and growing juvenile feathers on different body parts. These field estimations have been validated later via photographical analysis. The age of the chicks alters between four and eight weeks. In this study we analysed the data of more than 480 chicks, which were ringed between 2012 and 2017. The primer pair that amplifies an intron (i16) of CHD1 gene was used in PCR reaction for sex determination of the collected samples. The results of molecular sexing and during the ringing collected body size and development stage data were analysed using the R statistical software. Decision trees and random forest methods were used to find the best variables to distinguish sex groups by morphology in all development stages.

According to our results the best variable was the hind claw length. Another important variable can be the tarsus diameter, which in contrast to the other body size measurements after age of four and a half weeks did not grow and with age the difference between males and females in tarsus diameter decreased, nevertheless this variable was the best for estimating sex of the youngest nestlings. In case of more developed chicks hind claw length and body mass were more appropriate for separating sex groups, since in case of these variables the difference between sexes was growing with age. Tail feathers continuously grow as chicks develop, therefore tail length was the best variable for age determination. According to these results a protocol can be introduced that can be proper for field sex determination.

A sex identification method based on morphological traits can be helpful in field research studies, if it is easy to use, inexpensive and with acceptable accuracy can estimate the sex of eastern imperial eagle’s nestlings.

*-HELICON LIFE project and PannonEagele LIFE project