# A multidisciplinary assessment of endocrine and morphometric correlates of lactation physiology in southern right whales

## TL;DR

This study explores how southern right whale mothers manage energy during lactation by combining body condition measurements with hormone analysis.

## Contribution

The study integrates photogrammetry and endocrine monitoring to provide new physiological insights into maternal investment in southern right whales.

## Key findings

- Glucocorticoids and triiodothyronine were positively correlated, especially in lactating females.
- Both hormones declined toward the end of the calving season, indicating reduced metabolic activity.
- No significant differences in hormone levels were found between demographic or body condition groups, possibly due to small sample size.

## Abstract

Reproduction in long-lived, iteroparous mammals requires careful allocation of energetic resources. This is especially true in capital breeding species such as the southern right whale (Eubalaena australis), where reproductive success depends on body condition, as accumulated reserves must fuel the high energetic demands, especially during lactation. Understanding the physiological mechanisms underpinning maternal energy balance is therefore critical for assessing reproductive capacity and maternal investment strategies. This study combined body condition metrics derived from aerial photogrammetry with endocrine correlates (glucocorticoids and triiodothyronine; hormones associated with energy mobilisation and regulation of metabolism) measured in blubber biopsies to establish baseline measures of metabolic function in lactating southern right whales over the calving season (July–September). Analyses revealed a positive correlation between glucocorticoids and triiodothyronine, strongest in lactating females. A clear decline in both hormones was observed toward the end of the calving season, consistent with reduced maternal metabolic activity and corresponding to slowed calf growth rates. No significant differences in hormone concentrations were detected between demographic groups (n = 15 lactating females, n = 8 unaccompanied adults), nor maternal (n = 9 good condition, n = 3 poor condition) or calf body condition categories (n = 5 good condition, n = 7 poor condition), although this may relate to the study’s limited sample size. By linking endocrine profiles with body condition, this study provides novel physiological context for understanding maternal investment strategies in southern right whales. The findings highlight how intra-seasonal energetic demands are hormonally mediated during lactation and demonstrate the feasibility of integrating photogrammetry with endocrine monitoring in free-swimming baleen whales. Establishing these physiological baselines is critical for detecting early indicators of reproductive stress and for informing conservation strategies in recovering populations.