Figure 2 - uploaded by Shane Dickeson
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(A) Example aerial photograph of a southern right whale used to measure body volume. Only photographs in which the whale was lying flat at the surface, with its dorsal side up and with a straight body axis and non-arching peduncle, were used in the. (B) Positions of measurement sites used in the study. The dotted line indicates the location of the eye width measurement, located at 25 and 20% body length from the rostrum for lactating females and calves, respectively. W: width (from Christiansen et al., 2018).
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Migrations are key events in the annual life cycle for many animal species, including baleen whales. Despite having some of the longest migrations among mammals, relatively little is known about what triggers migration behaviour in baleen whales, and how intrinsic and extrinsic factors influence the timing of migrations. This study investigated the...
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... ideal for sampling were considered those of a whale situated flat at the surface, dorsal side facing up, with straight body axis and peduncle that was non-arching ( Figure 2) ( Christiansen et al., 2016aChristiansen et al., , 2018). The UAV operator was able to remotely view and correct the position of the UAV above a whale. ...
Citations
... With absolute energy reserves being highly correlated to BL (Lockyer, 1976), longer individuals are able to store more energy reserves compared to shorter individuals (Irvine et al., 2017). Longer females should therefore be able to grow their calves faster (Christiansen et al., 2018) until the calves reached the minimum size threshold needed to survive the migration to their feeding grounds (Dickeson, 2018). Because there is little apparent benefit in extending residency times for cow/calf pairs beyond this point, we would expect cow/calf pairs to leave the breeding grounds as soon as the calf reaches a minimum biological size. ...
Migratory humpback whales ( Megaptera novaeangliae ) cover the cost of reproduction in low‐latitude breeding grounds with stored energy accumulated from polar feeding grounds. The ability to accumulate sufficient energy reserves during feeding periods is vital for key life history stages during migration, including mating, calving, and lactation. This study aimed to investigate the relationship between migration timing and body condition of Western Australian humpback whales. We used unmanned aerial vehicles to measure body condition (residual of body volume vs. length) in 2017 and 2021. Morphometric measurements were obtained from 460 individuals (71 calves, 83 juveniles, 235 adults, and 71 lactating females) during the northbound (toward breeding grounds) and southbound (toward feeding grounds) migration between May and November. Body condition decreased by 23 and 13 percentage points for juveniles and adults, respectively. The body condition of juveniles was shown to be correlated with migration timing for their northern migration, with individuals in better body condition migrating to the breeding grounds earlier. While stored energy is vital for humpback whales to successfully complete their vast migration to‐and‐from breeding grounds, we found no evidence that body condition affects the migration timing for adults, lactating females, and calves.
... Despite not finding a significant positive relationship during this study, the model indicated weak evidence for such a trend. The migration timing of cow/calf southern right whale E. australis pairs in South Australia were influenced mostly by diurnal period, followed by calf size, sea surface temperature, and lastly maternal body condition (Dickeson 2018). The authors concluded that calf size, rather than maternal size, facilitates migration from breeding grounds. ...
In order to exploit seasonally favourable habitats for feeding and breeding, humpback whales Megaptera novaeangliae undertake one of the longest migrations in the animal kingdom. Stored energy is crucial for a successful migration, but few studies have investigated the relationship between migration timing and body condition in baleen whales. Using unmanned aerial vehicles, we quantified the body condition of east Australian humpback whales. We collected data on 513 individuals (48 calves, 166 juveniles, 251 adults, and 48 lactating females) during their northbound and southbound migrations between June and October 2020. For adults and juveniles, we explored the loss of body condition between migration direction (north versus south) as well as the relationship of migration timing (day of year) and body condition. We found a significant loss in body condition between the northbound and southbound migrations for both adults (9.8%) and juveniles (18.3%). However, migration timing did not influence body condition for either reproductive class. Cow/calf pairs were analysed using relative calf length (percentage of maternal length) as a proxy for days postpartum. We found a positive curvilinear relationship between migration timing and calf body condition. However, lactating females showed no relationship between migration timing and body condition. Whilst body condition is important for capital breeding whales, the lack of a correlation found for adults and juveniles suggests that body condition is not the main driver of migration timing from feeding or breeding grounds. However, calf body condition may be a significant factor for the migration timing of cow/calf pairs.
Climate change is causing the poleward range‐shift of many species, with consequent modifications to daylight regimes and potential impacts on light‐cycle activity patterns and ecological interactions.
Day‐active parasitoids experiencing longer summer days associated with a poleward range shift display increased attack rates on their aphid hosts and have higher lifetime fecundity. Theory consequently predicts that with increasing photoperiod, host–parasitoid interactions would become less stable with more variable population densities and increased extinction probability.
To test this prediction empirically, we conducted a multigenerational aphid‐parasitoid microcosm experiment in which we followed population dynamics under 14 and 18 h daylight treatments.
As predicted, we found an increased extinction rate of both aphids and parasitoids with longer daylengths. The long‐day treatments also exhibited higher temporal variation in parasitoid numbers and increased cumulative parasitoid population size, consistent with the prediction that increased aphid extinctions are due to increased parasitoid attack rates.
Our results demonstrate that light regime can affect the dynamics of interacting species and potentially limit the co‐existence of hosts and parasitoids, as well as other trophically interacting taxa where activity patterns are dependent on the light regime. This highlights the importance of the rarely considered effect of changing daylight conditions associated with climate change–driven range shifts, which could limit poleward range shifts due to changing ecological interactions.
