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 environment. Such behavioural rhythms are well studied in isolated individuals under laboratory conditions, but free-living individuals have to temporally synchronize their activities with those of others, including potential mates, competitors, prey and predators. Individuals can temporally segregate their daily activities (for example, prey avoiding predators, subordinates avoiding dominants) or synchronize their activities (for example, group foraging, communal defence, pairs reproducing or caring for offspring). The behavioural rhythms that emerge from such social synchronization and the underlying evolutionary and ecological drivers that shape them remain poorly understood. Here we investigate these rhythms in the context of biparental care, a particularly sensitive phase of social synchronization 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 parent's incubation bout varied from 1-19 h, whereas period length-the time in which a parent's probability to incubate cycles once between its highest and lowest value-varied from 6-43 h. 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 who 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 captivity. The risk of predation, not the risk of starvation, may be a key factor underlying the diversity in these rhythms.</p

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, 2, 3, 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, 7, 8, 9, 10. Individuals can temporally segregate their daily activities (for example, prey avoiding predators, subordinates avoiding dominants) or synchronize their activities (for example, group foraging, communal defence, pairs reproducing or caring for offspring)6, 7, 8, 9, 11. The behavioural rhythms that emerge from such social synchronization and the underlying evolutionary and ecological drivers that shape them remain poorly understood5, 6, 7, 9. Here we investigate these rhythms 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 parent’s incubation bout varied from 1–19 h, whereas period length—the time in which a parent’s probability to incubate cycles once between its highest and lowest value—varied from 6–43 h. 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 who 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, 6, 7, 9. The risk of predation, not the risk of starvation, may be a key factor underlying the diversity in these rhythms

Fig. 5 in Effects of Forest Roads on Spatial Distribution of Boreal Carabid Beetles (Coleoptera: Carabidae)

Fig. 5. Multivariate Regression Trees for the forest and roadside catches (a) and for the roadside catches only (b). The column graphs show the carabid abundances (27 species included) sorted according to the rank-abundance order of the total sample; scales are log10. For a species list sorted accordingly, see Table 1. The values in parentheses show how many samples (traps) fell into a given end branch. The dash-line box in (a) indicates the result of MRT for forest samples only; for further details, see text.Published as part of &lt;i&gt;Koivula, Matti J., 2005, Effects of Forest Roads on Spatial Distribution of Boreal Carabid Beetles (Coleoptera: Carabidae), pp. 465-487 in The Coleopterists Bulletin 59 (4)&lt;/i&gt; on page 474, DOI: 10.1649/815.1, &lt;a href="http://zenodo.org/record/10105193"&gt;http://zenodo.org/record/10105193&lt;/a&gt

Fig. 2 in Effects of Forest Roads on Spatial Distribution of Boreal Carabid Beetles (Coleoptera: Carabidae)

Fig. 2. Study designs of the Hyytiälä and Pornainen studies, and the geographical locations of the two studies. Box shows the area mapped in Figure 1. a. The Hyytiälä study. Black dots indicate pitfall traps operating between 15 May and 23 September, hollow circles indicate traps added in 28 June. b. The Pornainen study. Black dots indicate pitfall traps. In (a) and (b), cross-hatched area is forest, white clear-cut (a) or open farmland (b).Published as part of &lt;i&gt;Koivula, Matti J., 2005, Effects of Forest Roads on Spatial Distribution of Boreal Carabid Beetles (Coleoptera: Carabidae), pp. 465-487 in The Coleopterists Bulletin 59 (4)&lt;/i&gt; on page 468, DOI: 10.1649/815.1, &lt;a href="http://zenodo.org/record/10105193"&gt;http://zenodo.org/record/10105193&lt;/a&gt

Effects of Forest Roads on Spatial Distribution of Boreal Carabid Beetles (Coleoptera: Carabidae)

Koivula, Matti J. (2005): Effects of Forest Roads on Spatial Distribution of Boreal Carabid Beetles (Coleoptera: Carabidae). The Coleopterists Bulletin 59 (4): 465-487, DOI: 10.1649/815.1, URL: http://dx.doi.org/10.1649/815.

Fig. 4 in Effects of Forest Roads on Spatial Distribution of Boreal Carabid Beetles (Coleoptera: Carabidae)

Fig. 4. Median catches of generalist and open-habitat carabids along the roadsides from the forest/clear-cut border. Specimens caught between 15 May and 23 September included. Note that only three roads were included for the open-habitat carabid graph (because of total catch of 1 in one road). For statistical significances of distance gradients, consult Table 2 and Appendix 2b.Published as part of &lt;i&gt;Koivula, Matti J., 2005, Effects of Forest Roads on Spatial Distribution of Boreal Carabid Beetles (Coleoptera: Carabidae), pp. 465-487 in The Coleopterists Bulletin 59 (4)&lt;/i&gt; on page 473, DOI: 10.1649/815.1, &lt;a href="http://zenodo.org/record/10105193"&gt;http://zenodo.org/record/10105193&lt;/a&gt

Fig. 1 in Effects of Forest Roads on Spatial Distribution of Boreal Carabid Beetles (Coleoptera: Carabidae)

Fig. 1. The road network in Häme, south-central Finland, in 1955 and in 2001. For the geographical location of the mapped area, see Figure 2. The maps are based on 1:250,000 (''GT'') maps, and complemented by adding forest roads from basic maps (1:20,000) to make them comparable. Boxes within maps show the Hyytiälä study area. Water bodies are shown in gray.Published as part of &lt;i&gt;Koivula, Matti J., 2005, Effects of Forest Roads on Spatial Distribution of Boreal Carabid Beetles (Coleoptera: Carabidae), pp. 465-487 in The Coleopterists Bulletin 59 (4)&lt;/i&gt; on page 466, DOI: 10.1649/815.1, &lt;a href="http://zenodo.org/record/10105193"&gt;http://zenodo.org/record/10105193&lt;/a&gt

Fig. 3 in Effects of Forest Roads on Spatial Distribution of Boreal Carabid Beetles (Coleoptera: Carabidae)

Fig. 3. Mean values of species richness and abundances of two carabid species for the roadside samples, and forest samples at distances 25 m and 50 m from the roadsides. Only specimens caught between 28 June and 23 September are included. For statistical significances, consult Table 2 and Appendix 2a.Published as part of &lt;i&gt;Koivula, Matti J., 2005, Effects of Forest Roads on Spatial Distribution of Boreal Carabid Beetles (Coleoptera: Carabidae), pp. 465-487 in The Coleopterists Bulletin 59 (4)&lt;/i&gt; on page 472, DOI: 10.1649/815.1, &lt;a href="http://zenodo.org/record/10105193"&gt;http://zenodo.org/record/10105193&lt;/a&gt