Suomeksi
 
 
Timing of building the nest in rabbits
​Rabbit pups in a nest with vegetational material and hair

​What goes on in the burrow?

Not much is known about naturally occurring nest mortality rates in small altricial mammals that give birth in difficult-to-access burrows or dens. One of the few well-studied species is the European rabbit, where mortality rates during the nest period have been shown to be high, approximately 40%. In a previous study, the occurrence of perinatal mortality was 12%. However, the causes of such perinatal mortality remained unexplained in more than 71% of cases. As nest quality was identified as an important factor influencing offspring survival in a study of domestic rabbits, it could be assumed that disturbances or delays in maternal burrow and nest building under natural conditions might possibly account, at least partly, for unexplained variation in perinatal mortality of wild European rabbits as well.
 
By analyzing a long-term data set (11 years) from a study on European rabbits living in a field enclosure of 2.0 ha, we tested whether late maternal burrow and nest building (all building activities during the last 24h pre-partum) increases the occurrence of perinatal offspring mortality. Additionally, we aimed to identify causes for the occurrence of such late burrow and nest building behaviour. We could classify 3 categories of maternal burrow and nest building behaviour:
Category A: 36.5% of cases; a nursery burrow dug by the female that contained vegetational nest material (but without abdominal hair) was already present at least 24 h prior to parturition. The females incorporated abdominal hair into the nest sometime during the 24 h prior to parturition.
Category B: 45.5% of cases; a nursery burrow was already present at least 24 h prior to parturition, but no nest material and abdominal hair were present in the burrow at this time. Nest material and abdominal hair were deposited by the female into the nursery burrow sometime during the 24 h prior to parturition.
Category C: 18.0% of cases (“late burrow and nest building”); all components of maternal nest building were carried out during the 24 h prior to parturition. Females dug a new nursery burrow including a terminal nest chamber and constructed a proper nest consisting of vegetational material and abdominal hair sometime during the 24 h prior to parturition.
 
Our key finding was that females which dug their burrow and constructed the nest during the last night before giving birth showed a significant higher perinatal offspring mortality than mothers that dug their burrow earlier. We furthermore suggest that late burrow and nest building is not an inherent reproductive strategy but is rather due to competition for breeding burrows. Agonistic social interactions between females were increased when different females of a group reproduced at around the same time. Overall, the findings support the conclusion that competition for breeding resources, in particular within smaller group territories, was an important driver for delays in maternal burrow and nest building. The results of our study in European rabbits suggest a pathway explaining how social factors could be involved in modulating early offspring survival, thus potentially contributing to mother’s reproductive fitness. These findings should have a broader relevance for other species of group-living mammals that construct burrows or nests for reproduction.

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-Martin Seltmann
4.5.2017
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