Biology subjects

Bulla, M.

Publications and source records attributed to Bulla, M..

5 recordsLinked to original sources

bioRxiv2018

Diverse incubation rhythms in a facultatively uniparental shorebird -- the Northern Lapwing

Incubation by both parents is the most common form of care for eggs. Although the involvement of the two parents may vary dramatically between and within pairs, as well as over the day and breeding season, detailed description of this variation (especially in species with variable male contribution to incubation) is rare. Here, we continuously video-monitored 113 nests of Northern Lapwing Vanellus vanellus over the breeding season to reveal the diversity of incubation rhythms and parental involvement. We found great between-nest variation in the overall nest attendance (68 -94%; median = 87%) and in how much males incubated (0 - 37%; median = 13%). Notably, the less the males incubated, the lower was the overall nest attendance, even though females partially compensated for the males decrease. Overall, incubation rhythms changed little over the season and incubation period. However, as nights shorten with the progressing breeding season, the female longest night incubation bout shortened too. Essentially, nest attendance was highest, incubation bouts longest, exchange gaps shortest and male involvement lowest during the night. Also, males tended to incubate the most after sunrise and before sunset. To conclude, we revealed strong circadian rhythms and remarkable between nest differences in Northern Lapwing incubation (especially in male involvement), yet despite seasonal environmental trends (e.g. increasing temperature) Lapwing incubation rhythms remained relatively stable over the season and incubation period.

animal behavior and cognition↗

bioRxiv2017

Methods in field chronobiology

Chronobiological research has seen a continuous development of novel approaches and techniques to measure rhythmicity at different levels of biological organization from locomotor activity (e.g. migratory restlessness) to physiology (e.g. temperature and hormone rhythms, and relatively recently also in genes, proteins and metabolites). However, the methodological advancements in this field have been mostly and sometimes exclusively used only in indoor laboratory settings. In parallel, there has been an unprecedented and rapid improvement in our ability to track animals and their behaviour in the wild. However, while the spatial analysis of tracking data is widespread, its temporal aspect is largely unexplored. Here, we review the tools that are available or have potential to record rhythms in the wild animals with emphasis on currently overlooked approaches and monitoring systems. We then demonstrate, in three question-driven case studies, how the integration of traditional and newer approaches can help answer novel chronobiological questions in free-living animals. Finally, we highlight unresolved issues in field chronobiology that may benefit from technological development in the future. As most of the studies in the field are descriptive, the future challenge lies in applying the diverse technologies to experimental set-ups in the wild.

animal behavior and cognition↗

bioRxiv2017

Temporary mate removal during incubation leads to variable compensation in a biparental shorebir

Biparental care for offspring requires cooperation, but it is also a potential source of conflict, since one parent may care less at the expense of the other. How, then, do parents respond to the reduction of their partners care? Theoretical models predict that parents that feed offspring should partially compensate for the reduced care of their partner. However, for incubating birds partial compensation is unlikely the optimal strategy, because the entire brood can fail with reduced care. Although biparental incubation dominates in non-passerine birds, short-term manipulations of parental care and evaluations of individual differences in the response, both crucial to our understanding of parental cooperation, are scarce. Here, we describe the response of semipalmated sandpiper (Calidris pusilla) parents to a 24-hour removal of their partner during the incubation period, explore factors that can explain individual variation in the response, and describe how incubation rhythms changed after the removed parent returned. On average, the parents compensated partially for the absence of their partners care (59%; 95%CI: 49-70%, N = 25 individuals). The level of compensation did not differ between the sexes. However, individual responses varied from no to full compensation (2-101%). In seven nests where the removed parent never returned, the widowed parent attended the nest for 0-10 days (median: 4 days). In contrast to patterns observed in undisturbed nests or in uniparental species, nest attendance during compensation tended to be higher during the warmer part of the day. Although the level of compensation was not related to the before-experimental share of incubation, more responsive parents (that left the nest earlier upon human approach) compensated more. The quality of incubation in the after-experimental period was lower than usual, but improved quickly over time. Our findings suggest that full compensation might be limited by energetic constraints or by variation in responsiveness to the absence of the partner. Nevertheless, semipalmated sandpiper parents are able to adjust their subsequent incubation behaviour to take full responsibility for the nest when widowed. Because (nearly) full compensation was the most common response, we speculate that all individuals attempt full compensation, but that some fail because their energy stores get depleted, or because they are less responsive to the absence of their partner.

animal behavior and cognition↗

bioRxiv2017

Flexible Parental Care: Uniparental Incubation In Biparentally Incubating Shorebirds

Recent findings suggest that relative investment of females and males into parental care depends on the populations adult sex-ratio. For example, all else being equal, males should be the more caring sex if the sex ratio is male biased. Whether such outcomes are evolutionary fixed (i.e. related to the species typical sex-ratio) or whether they arise through flexible responses of individuals to the current population sex-ratio remains unclear. Nevertheless, a flexible response might be limited by evolutionary history when one sex loses the ability to care or when a single parent cannot successfully care. Here, we demonstrate that after the disappearance of one parent, individuals from 8 out of 15 biparentally incubating shorebird species were able to incubate uniparentally for 1-19 days (median = 3, N = 69). Such uniparental phases often resembled the incubation rhythm of species with obligatory uniparental incubation. Although it has been suggested that females of some shorebirds desert their brood after hatching, our findings indicate that either sex may desert prior to hatching. Strikingly, in 27% of uniparentally incubated clutches - from 5 species - we document successful hatching. Our data thus reveal the potential for a flexible switch from biparental to uniparental care.

evolutionary biology↗

bioRxiv2016

Unexpected diversity in socially synchronized rhythms of shorebirds

The behavioural rhythms of organisms are thought to be under strong selection, influenced by the rhythmicity of the environment1-4. Such behavioural rhythms are well studied in isolated individuals under laboratory conditions1,5, but free-living individuals have to temporally synchronize their activities with those of others, including potential mates, competitors, prey and predators6-10. Individuals can temporally segregate their daily activities (e.g. prey avoiding predators, subordinates avoiding dominants) or synchronize their activities (e.g. group foraging, communal defence, pairs reproducing or caring for offspring)6-9,11. The behavioural rhythms that emerge from such social synchronization and the underlying evolutionary and ecological drivers that shape them remain poorly understood5-7,9. Here, we address this in the context of biparental care, a particularly sensitive phase of social synchronization12 where pair members potentially compromise their individual rhythms. Using data from 729 nests of 91 populations of 32 biparentally-incubating shorebird species, where parents synchronize to achieve continuous coverage of developing eggs, we report remarkable within- and between-species diversity in incubation rhythms. Between species, the median length of one parents incubation bout varied from 1 - 19 hours, while period length-the time in which a parents probability to incubate cycles once between its highest and lowest value - varied from 6 - 43 hours. The length of incubation bouts was unrelated to variables reflecting energetic demands, but species relying on crypsis (the ability to avoid detection by other animals) had longer incubation bouts than those that are readily visible or actively protect their nest against predators. Rhythms entrainable to the 24-h light-dark cycle were less prevalent at high latitudes and absent in 18 species. Our results indicate that even under similar environmental conditions and despite 24-h environmental cues, social synchronization can generate far more diverse behavioural rhythms than expected from studies of individuals in captivity5-7,9. The risk of predation, not the risk of starvation, may be a key factor underlying the diversity in these rhythms.

animal behavior and cognition↗