Data from: High suckling rates and acoustic crypsis of humpback whale neonates maximise potential for mother–calf energy transfer

1. The migration of humpback whales to and from their breeding grounds results in a short, critical time period during which neonatal calves must acquire sufficient energy via suckling from their fasting mothers to survive the long return journey. 2. Understanding neonate suckling behaviour is critical for understanding the energetics and evolution of humpback whale migratory behaviour and for informing conservation efforts, but despite its importance, very little is known about the details, rate and behavioural context of this critical energy transfer. 3. To address this pertinent data gap on calf suckling behaviour, we deployed multi-sensor Dtags on eight humpback whale calves and two mothers allowing us to analyse detailed suckling and acoustic behaviour for a total of 68·8 h. 4. Suckling dives were performed 20·7 ± 7% of the total tagging time with the mothers either resting at the surface or at depth with the calves hanging motionless with roll and pitch angles close to zero. 5. Vocalisations between mother and calf, which included very weak tonal and grunting sounds, were produced more frequently during active dives than suckling dives, suggesting that mechanical stimuli rather than acoustic cues are used to initiate nursing. 6. Use of mechanical cues for initiating suckling and low level vocalisations with an active space of <100 m indicate a strong selection pressure for acoustic crypsis. 7. Such inconspicuous behaviour likely reduces the risk of exposure to eavesdropping predators and male humpback whale escorts that may disrupt the high proportion of time spent nursing and resting, and hence ultimately compromise calf fitness. 8. The small active space of the weak calls between mother and calf is very sensitive to increases in ambient noise from human encroachment thereby increasing the risk of mother–calf separation.

1. 座头鲸往返繁殖地的洄游会造就一段短暂且关键的时期，此时新生幼崽必须通过吸食禁食母体获取足够能量，方能完成漫长的返程旅程。
2. 阐明幼崽哺乳行为，对于理解座头鲸洄游行为的能量代谢与演化、为保护工作提供参考均至关重要；但尽管其意义重大，学界对这一关键能量传递过程的细节、速率及行为背景仍知之甚少。
3. 为填补这一有关幼崽哺乳行为的关键数据空白，我们为8头座头鲸幼崽与2头成年母鲸部署了多传感器D标签（Dtags），总计获得68.8小时的详细哺乳与声学行为分析数据。
4. 哺乳潜行为占总标记时长的20.7±7%，此时母体或静息于海面，或潜至水下，幼崽则保持静止悬停，翻滚角与俯仰角均接近0度。
5. 母子间的发声包含极微弱的单音与咕哝声，其出现频率在主动潜航时高于哺乳潜航，这表明哺乳行为的启动依赖机械刺激而非声学线索。
6. 哺乳启动依赖机械刺激、且有效发声空间不足100米的低强度发声，这显示出声学隐蔽性存在极强的选择压力。
7. 这种不显眼的行为或可降低被窃听捕食者、以及可能干扰哺乳与静息占比极高时段的雄性座头鲸护卫者发现的风险，最终保障幼崽的生存适合度。
8. 母子间微弱叫声的极小有效发声空间，对人类活动侵扰带来的环境噪声增加极为敏感，进而提升了母子分离的风险。