Investigating the value of incorporating behavioural measures in a discriminant function developed for sex assignment in black-capped chickadees (Poecile atricapillus)

• Author / Creator

  Sridharan, Sheeraja

• Black-capped chickadees (Poecile atricapillus) are a sexually monomorphic species that typically require molecular assays or observation of sex-specific behaviours in the breeding season for accurate sex assignment. We developed a discriminant function in a central Albertan chickadee population using 469 individuals (238 females and 231 males) for the purpose of future sex assignment in the same population. We used morphometric measurements in the development of our model and investigated the potential value of incorporating behavioural measurements to improve correct sex assignment rates in the discriminant function. In total, we evaluated the utility of five measures of morphological traits (i.e., body mass, wing length, tarsus length, bill length and bill depth) and four measures of behavioural traits (exploration, handling aggression, daily foraging rate and foraging inter-visit interval (IVI) for developing a discriminant function. We compared a model consisting of all morphological traits with a model consisting only of highly repeatable morphological traits (i.e., body mass, wing length, tarsus length) and found they yielded comparable accuracy rates of 86% (84.8% Males, 87.2% Females) and 89.2% (91.3% males and 87.2% females), respectively. This demonstrates that at large enough sample sizes, inclusion of additional traits does not result in considerable increase in model accuracy and in fact, may run the risk of introducing error into model as a consequence of measurement errors. The model using only repeatable morphological traits also revealed clear cut off points in the discriminant score to assign sex to males (discriminant scores >81) and females (discriminant scores <77). However, 31.1% of individuals within our population fall within the intermediate score range and consequently will require alternative sex confirmation techniques. We also ran a third model on a subset of our study population (155 individuals: 82 males, 73 females) using all morphological traits and the only behavioural trait (foraging IVI) for which significant sex differences were found, to evaluate the utility of using behavioural traits to improve sex assignment rates in discriminant functions. This model produced an overall accuracy of 90% (93.8% males, 85.7% females) with similarly high model accuracies obtained when compared to alternative models with i) all the morphological traits and no behavioural traits, and ii) only highly repeatable morphological traits and no behavioural traits. In our study, the measured behavioural traits did not improve the accuracy of the discriminant function. We discuss reasons why this might be the case and propose other behaviours that might be useful to consider for future work. Ultimately, in this study we were able to exhibit the value of capitalising on simple, easy to measure morphometric traits to accurately assign sex in species with cryptic morphological differences between sexes.

• Subjects / Keywords

  • Sex determination
  • Black-capped chickadees
  • Poecile atricapillus
  • Discriminant function
  • Morphometric traits
  • Behavioural traits

• Graduation date

  Fall 2021

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-3g1k-0f57

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.