A mother’s age and her experience usually increase together. That makes a familiar question surprisingly difficult to answer: does maternal behaviour change because an animal is older, or because she has raised calves before?
For giraffes, the distinction matters when interpreting the time a female allows a calf at her udder. An older mother might allocate more to her current calf because fewer future breeding opportunities remain. An experienced mother might also recognise and respond to nursing attempts differently. Those explanations overlap, but they describe different processes.
Markéta Gloneková, Karolína Brandlová and Jan Pluháček tackled this problem in a study of maternal care in four Czech zoos. Females with more previous births generally spent more time nursing, including calves other than their own. Comparing alternative explanations suggested that reproductive experience accounted for some of the variation better than age alone.
Counting experience as well as birthdays
The team observed 22 nursing females and 47 calves over 876.5 hours. The females ranged from five to 23 years old and had given birth between once and eleven times. That range gave the researchers more to work with than a simple comparison of young and old mothers.
They recorded nursing attempts as well as longer bouts. An approach that ended quickly could reveal rejection even though it contributed almost nothing to total nursing time. The researchers therefore asked several related questions: how frequently did nursing occur, how much time did it occupy, and how often did an attempt succeed?
These are different aspects of maternal behaviour. A female could allow many brief bouts, or fewer long ones. She could also reject most approaches while allowing a small number of substantial bouts. One measure alone would conceal those differences.
Because age and previous births were closely linked, the researchers compared models containing one or the other. This is like asking which description of a mother better predicts her observed behaviour, while accounting for other measured differences. It does not create the clean separation that an experiment would provide: the same females still supplied both their ages and their reproductive histories.
Acceptance carried the clearest signal
The evidence did not give reproductive experience an equally strong advantage for every measurement. Models based on previous births were especially well supported for the probability that a nursing attempt succeeded. They also tended to fit nursing time better. For frequency, the difference between age and experience was small or absent in some comparisons.
That unevenness is informative. It suggests that experience may be particularly relevant to whether a mother permits an approach to develop into nursing, rather than simply setting the number of encounters in an hour. The overall association between previous births and nursing frequency was also less secure than the relationship with nursing time.
The pattern extended beyond a female’s own offspring. More experienced mothers generally devoted more nursing time to other calves as well. This makes the result more than a story about an older mother investing heavily in her latest calf: it also raises a question about changing tolerance within a group.
Calf age mattered too. Nursing time declined as calves grew older. Comparing mothers without allowing for the ages of the calves around them would risk confusing a normal developmental change with a difference in maternal behaviour.
Nursing time is a social measure
The observers could see a calf’s position and how long it remained at the udder. They could not measure the volume or composition of milk it received. The finding is therefore about nursing behaviour and access, rather than a measured increase in nutritional investment.
That distinction also helps explain why another female’s calf is scientifically interesting. Allowing contact may reflect tolerance, recognition, or the circumstances of the encounter, alongside any milk transferred. A longer bout does not by itself reveal which process changed.
The authors discuss experience alongside the possibility that mothers with fewer reproductive opportunities ahead invest more in their current young. The better performance of several experience-based models points toward learning or accumulated maternal practice as a useful explanation. It does not establish that learning caused the difference. Individual temperament, health and reproductive history were not randomly assigned.
Food was regularly supplied in these zoos, and the giraffes did not face the same constraints as females finding sufficient browse in the wild. The authors suggest that these conditions could help permit tolerance. That remains a proposed explanation for the setting, rather than a tested effect of abundant food.
Following a mother across successive calves
The study belongs to a connected programme of nursing research. The team’s work on why giraffes nurse other females’ calves examines reciprocity and opportunistic access using the same broader observations. Those papers offer different questions about a shared dataset, not independent confirmations from new populations.
A particularly useful next comparison would follow individual females across successive births, asking whether their own acceptance changes. That would reduce the risk of mistaking stable differences between females for an effect of gaining experience, although ageing would still occur alongside each new birth.
Another question is whether access and nutrition change together. Growth records alongside nursing observations could test whether calves receiving more nursing time also grow differently, while recognising that growth depends on far more than milk. In the meantime, the result gives keepers and researchers a concrete reason to consider a mother’s reproductive history when interpreting her tolerance: maternal behaviour varies along a life history, not simply between attentive and inattentive individuals.
Sources
- 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.
- Markéta Gloneková, Karolína Brandlová and Jan Pluháček (2021). Further behavioural parameters support reciprocity and milk theft as explanations for giraffe allonursing. Scientific Reports 11, 7024. DOI: 10.1038/s41598-021-86499-2. Open full text.
