A calf can stop suckling, but so can the female feeding it. That simple distinction changes what a longer nursing bout might mean. A calf may remain interested for longer, a mother may tolerate it for longer, or both may contribute to the same observed duration.
Markéta Gloneková, Karolína Brandlová and Jan Pluháček used that distinction to investigate sex differences in giraffe suckling. Male calves stayed at the udder longer than females in the observed bouts. The difference persisted when the team restricted the comparison to bouts that the nursing female ended.
The result makes maternal behaviour part of the explanation, while leaving open how much the calves’ own persistence contributed. It also illustrates why timing a feeding interaction can reveal something useful without telling us how much food was consumed.
Why a son might nurse differently
Adult male giraffes are considerably larger than females. The researchers therefore expected differences in early care to be plausible: males and females have different growth trajectories, and a calf’s demands may differ accordingly.
There are at least two routes to longer nursing. A mother could allow a male calf more time, or a male calf could make greater efforts to continue. Observations of the final duration cannot neatly divide those influences. A feeding interaction emerges from the behaviour of both participants.
To investigate it, the team drew on observations of 22 nursing females and 47 calves in four Czech zoos. They recorded suckling across 876.5 hours of observation, identifying individuals and noting whether the female sniffed the calf, its position, and who ended the bout.
For this analysis, only bouts involving one calf at a time were used. That restriction mattered because several calves at an udder can interfere with one another or exploit an opportunity created by another calf. The question here was what happened during a single calf’s access to a female.
Who called time on the bout?
The reported set contained 352 bouts: 268 involved the female’s own calf and 84 involved another calf. A typical bout was brief; the overall mean duration was about sixteen seconds. The researchers compared durations while taking repeated observations of the same individuals and other recorded factors into account.
They then narrowed the analysis in stages. First came all eligible bouts. Next came only those ended by the female. Finally, they considered female-ended bouts involving her own calf.
Male calves had longer bouts in all three comparisons. The last comparison is particularly useful because it reduces two alternative complications at once: a calf deciding for itself when to leave, and a female responding to another mother’s offspring.
Even this does not reveal a conscious maternal preference for sons. A mother’s response may depend on how a calf approaches, persists or stimulates nursing. What the study shows is that the sex difference was still present in interactions whose ending the female controlled.
Nor did the team measure milk transfer. Sixteen seconds at an udder cannot be converted into a volume of milk without knowing whether milk was flowing, at what rate, and under what conditions. Nursing duration here is a measure of behaviour and tolerated access.
A sniff did not necessarily end the encounter
The researchers also found longer bouts when the female sniffed the calf. This association appeared in each of the three analyses.
Sniffing can provide information about a calf’s identity. It would be tempting to assume that recognising another female’s calf should lead to rejection, but that was not the simple pattern in these observations. Longer bouts associated with sniffing occurred beyond an exclusive mother–offspring relationship.
The direction of the association remains uncertain. Sniffing might be part of an interaction in which the female accepts prolonged contact. A longer bout also gives her more opportunity to sniff. The study observed these events together; it did not experimentally add or remove scent information.
Position offered another clue. In the full comparison, bouts were longer when the calf faced in the opposite direction to the female than when both faced the same way. That places the calf’s hindquarters nearer the female’s head and can make investigation easier. The position effect was not equally evident in every restricted analysis, so it should not become a universal rule about the best way to nurse.
One dataset, several aspects of care
This research belongs alongside the team’s study of maternal experience and its work on nursing other females’ calves. They draw on the same broader observation programme. Their value is in separating questions that would otherwise be bundled together: which females tolerate attempts, why non-offspring gain access, and how the calf’s sex relates to an individual bout.
For husbandry, the study argues for looking beyond a single stopwatch reading. Who initiated and ended the bout, whether the calf was accepted repeatedly, and whether its growth remained appropriate all change the interpretation. A brief bout by a female calf cannot be labelled inadequate solely because male calves averaged longer in this study.
Following calves’ growth alongside these interactions would help establish whether longer access predicts developmental differences. Recording the sequence before a female ends a bout could also clarify whether male calves persist differently. Both questions would extend the finding without treating behavioural time as a substitute for nutrition: the discovery is that male and female calves participated differently in this shared interaction.
Sources
- Markéta Gloneková, Karolína Brandlová and Jan Pluháček (2020). Giraffe males have longer suckling bouts than females. Journal of Mammalogy 101(2), 558–563. DOI: 10.1093/jmammal/gyz201. Author-uploaded full text.
- Markéta Gloneková, Karolína Brandlová and Jan Pluháček (2020). Higher maternal care and tolerance in more experienced giraffe mothers. Acta Ethologica 23, 1–7. DOI: 10.1007/s10211-019-00328-4. Author-uploaded full text.
