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Influence of Seasonal Food Availability on the Dynamics of Seabird Feeding Flocks at a Coastal Upwelling Area.

Anguita C, Simeone A - PLoS ONE (2015)

Bottom Line: However, there is scant information on the temporal stability of the composition and abundance of MSFFs as well as the effect of seasonal food availability on their dynamics.Using generalized linear models (GLMs), our results show that the contrasting seasonality in food availability of the study area (using chlorophyll-a concentration as a proxy) had no significant influence on MSFF attributes, sparsely explaining their variations (P>0.05).This would allow them to reduce resource unpredictability, which in turn has a major impact on structuring seabird's MSFF dynamics.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Ecología y Biodiversidad, Facultad de Ecología y Recursos Naturales, Universidad Andrés Bello, Santiago, Chile.

ABSTRACT
The formation of multi-species feeding flocks (MSFFs) through visual recruitment is considered an important strategy for obtaining food in seabirds and its functionality has been ascribed to enhanced foraging efficiency. Its use has been demonstrated in much of the world's oceans and includes numerous species. However, there is scant information on the temporal stability of the composition and abundance of MSFFs as well as the effect of seasonal food availability on their dynamics. Between July 2006 and September 2014, we conducted monthly at-sea seabird counts at Valparaiso Bay (32°56' to 33°01'S, 71°36' to 71°46'W) within the area of influence of the Humboldt Current in central Chile. This area is characterized by a marked seasonality in primary and secondary production associated with upwelling, mainly during austral spring-summer. Based on studies that provide evidence that flocking is most frequent when food is both scarce and patchy, we hypothesized that seabird MSFF attributes (i.e. frequency of occurrence, abundance and composition) will be modified according to the seasonal availability of food. Using generalized linear models (GLMs), our results show that the contrasting seasonality in food availability of the study area (using chlorophyll-a concentration as a proxy) had no significant influence on MSFF attributes, sparsely explaining their variations (P>0.05). Rather than seasonal food availability, the observed pattern for MSFF attributes at Valparaiso Bay suggests a substantial influence of reproductive and migratory (boreal and austral migrants) habits of birds that modulates MSFF dynamics consistently throughout the whole year in this highly variable and patchy environment. We highlight the importance of visual recruitment as a mechanism by which migratory and resident birds interact. This would allow them to reduce resource unpredictability, which in turn has a major impact on structuring seabird's MSFF dynamics.

No MeSH data available.


Box-plot of seasonal variation of MSFF attributes at Valparaiso Bay.(a) MSFF frequency of occurrence (MSFFs observed per month) and (b) MSFF abundance (total number of individuals observed in MSFFs per month). Insert (4a top) shows the monthly probability (± 95% confidence interval) of observing MSFFs per season (GLM, binomial structure). x shows the mean.
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pone.0131327.g004: Box-plot of seasonal variation of MSFF attributes at Valparaiso Bay.(a) MSFF frequency of occurrence (MSFFs observed per month) and (b) MSFF abundance (total number of individuals observed in MSFFs per month). Insert (4a top) shows the monthly probability (± 95% confidence interval) of observing MSFFs per season (GLM, binomial structure). x shows the mean.

Mentions: During the study period, we observed 38 species at Valparaiso Bay, of which 71% were engaged in MSFFs (Tables 1 and 2) and a total of 736 MSFFs; 16% in autumn, 41% in winter, 24% in spring and 20% in summer. The frequency of occurrence of MSFFs showed marginally significant seasonal differences (P = 0.053, Table 3A, Fig 4A), with the greatest frequency of occurrence in winter with an average of 12 MSFFs per month. In addition, winter presented the maximum probability of observing MSFFs per month (88%, Fig 4A top). Similarly, total abundance of individuals (birds per month) in MSFFs (Fig 4B) was highest in winter, but differences between seasons were not significant (P>0.05; Table 3B). Neither chlorophyll-a concentration nor its interaction with seasonality had a significant effect on the variation of both MSFF attributes (P>0.05; Table 3).


Influence of Seasonal Food Availability on the Dynamics of Seabird Feeding Flocks at a Coastal Upwelling Area.

Anguita C, Simeone A - PLoS ONE (2015)

Box-plot of seasonal variation of MSFF attributes at Valparaiso Bay.(a) MSFF frequency of occurrence (MSFFs observed per month) and (b) MSFF abundance (total number of individuals observed in MSFFs per month). Insert (4a top) shows the monthly probability (± 95% confidence interval) of observing MSFFs per season (GLM, binomial structure). x shows the mean.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4488391&req=5

pone.0131327.g004: Box-plot of seasonal variation of MSFF attributes at Valparaiso Bay.(a) MSFF frequency of occurrence (MSFFs observed per month) and (b) MSFF abundance (total number of individuals observed in MSFFs per month). Insert (4a top) shows the monthly probability (± 95% confidence interval) of observing MSFFs per season (GLM, binomial structure). x shows the mean.
Mentions: During the study period, we observed 38 species at Valparaiso Bay, of which 71% were engaged in MSFFs (Tables 1 and 2) and a total of 736 MSFFs; 16% in autumn, 41% in winter, 24% in spring and 20% in summer. The frequency of occurrence of MSFFs showed marginally significant seasonal differences (P = 0.053, Table 3A, Fig 4A), with the greatest frequency of occurrence in winter with an average of 12 MSFFs per month. In addition, winter presented the maximum probability of observing MSFFs per month (88%, Fig 4A top). Similarly, total abundance of individuals (birds per month) in MSFFs (Fig 4B) was highest in winter, but differences between seasons were not significant (P>0.05; Table 3B). Neither chlorophyll-a concentration nor its interaction with seasonality had a significant effect on the variation of both MSFF attributes (P>0.05; Table 3).

Bottom Line: However, there is scant information on the temporal stability of the composition and abundance of MSFFs as well as the effect of seasonal food availability on their dynamics.Using generalized linear models (GLMs), our results show that the contrasting seasonality in food availability of the study area (using chlorophyll-a concentration as a proxy) had no significant influence on MSFF attributes, sparsely explaining their variations (P>0.05).This would allow them to reduce resource unpredictability, which in turn has a major impact on structuring seabird's MSFF dynamics.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Ecología y Biodiversidad, Facultad de Ecología y Recursos Naturales, Universidad Andrés Bello, Santiago, Chile.

ABSTRACT
The formation of multi-species feeding flocks (MSFFs) through visual recruitment is considered an important strategy for obtaining food in seabirds and its functionality has been ascribed to enhanced foraging efficiency. Its use has been demonstrated in much of the world's oceans and includes numerous species. However, there is scant information on the temporal stability of the composition and abundance of MSFFs as well as the effect of seasonal food availability on their dynamics. Between July 2006 and September 2014, we conducted monthly at-sea seabird counts at Valparaiso Bay (32°56' to 33°01'S, 71°36' to 71°46'W) within the area of influence of the Humboldt Current in central Chile. This area is characterized by a marked seasonality in primary and secondary production associated with upwelling, mainly during austral spring-summer. Based on studies that provide evidence that flocking is most frequent when food is both scarce and patchy, we hypothesized that seabird MSFF attributes (i.e. frequency of occurrence, abundance and composition) will be modified according to the seasonal availability of food. Using generalized linear models (GLMs), our results show that the contrasting seasonality in food availability of the study area (using chlorophyll-a concentration as a proxy) had no significant influence on MSFF attributes, sparsely explaining their variations (P>0.05). Rather than seasonal food availability, the observed pattern for MSFF attributes at Valparaiso Bay suggests a substantial influence of reproductive and migratory (boreal and austral migrants) habits of birds that modulates MSFF dynamics consistently throughout the whole year in this highly variable and patchy environment. We highlight the importance of visual recruitment as a mechanism by which migratory and resident birds interact. This would allow them to reduce resource unpredictability, which in turn has a major impact on structuring seabird's MSFF dynamics.

No MeSH data available.