Limits...
Group foraging in Socotra cormorants: A biologging approach to the study of a complex behavior

View Article: PubMed Central - PubMed

ABSTRACT

Group foraging contradicts classic ecological theory because intraspecific competition normally increases with aggregation. Hence, there should be evolutionary benefits to group foraging. The study of group foraging in the field remains challenging however, because of the large number of individuals involved and the remoteness of the interactions to the observer. Biologging represents a cost‐effective solution to these methodological issues. By deploying GPS and temperature–depth loggers on individuals over a period of several consecutive days, we investigated intraspecific foraging interactions in the Socotra cormorant Phalacrocorax nigrogularis, a threatened colonial seabird endemic to the Arabian Peninsula. In particular, we examined how closely birds from the same colony associated with each other spatially when they were at sea at the same time and the distance between foraging dives at different periods of the day. Results show that the position of different birds overlapped substantially, all birds targeting the same general foraging grounds throughout the day, likely following the same school of fish. There were as many as 44,500 birds within the foraging flock at sea at any time (50% of the colony), and flocking density was high, with distance between birds ranging from 8 to 1,380 m. Birds adopted a diving strategy maximizing time spent underwater relative to surface time, resulting in up to 72% of birds underwater in potential contact with prey at all times while foraging. Our data suggest that the benefits of group foraging outweigh the costs of intense aggregation in this seabird. Prey detection and information transmission are facilitated in large groups. Once discovered, shoaling prey are concentrated under the effect of the multitude. Fish school cohesiveness is then disorganized by continuous attacks of diving birds to facilitate prey capture. Decreasing population size could pose a risk to the persistence of threatened seabirds where group size is important for foraging success.

No MeSH data available.


Diving behavior of Socotra cormorants. (a) Relationship between dive duration and maximum dive depth (black circles, y = 2.20x + 8.84, R2 = .69, P < .0001, n = 5,225) and frequency distribution of dive depth (gray vertical bars, n = 5,225). (b) Relationship between dive duration/postdive interval (PDI) and dive duration (black circles, y = 4.11ea, R2 = .06, P < .0001, n = 5,205) and frequency distribution of dive duration (gray vertical bars, n = 5,225)
© Copyright Policy - creativeCommonsBy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5383476&req=5

ece32750-fig-0008: Diving behavior of Socotra cormorants. (a) Relationship between dive duration and maximum dive depth (black circles, y = 2.20x + 8.84, R2 = .69, P < .0001, n = 5,225) and frequency distribution of dive depth (gray vertical bars, n = 5,225). (b) Relationship between dive duration/postdive interval (PDI) and dive duration (black circles, y = 4.11ea, R2 = .06, P < .0001, n = 5,205) and frequency distribution of dive duration (gray vertical bars, n = 5,225)

Mentions: Dive parameters are summarized in Table 2. Birds dived to shallow depths, with 22% and 92% of dives carried out to depths ≤2 and 15 m, respectively (Figure 8a). Accordingly, dive durations were short, with 67% of dives ≤30 s and 93% ≤45 s (Figure 8b). Dive duration increased linearly with maximum dive depth (Figure 8a). Frequency distribution of dive durations peaked for dives lasting 15–30 s and then decreased. Concomitantly, the dive duration/postdive interval ratio peaked for dives lasting 15–30 s, before decreasing (Figure 8b). Birds therefore favored a diving behavior that maximized the proportion of time spent underwater relative to the proportion spent at the surface. Dive profiles were parabolic (9.1%), V‐shaped (27.2%), irregular (28.2%), and flat‐bottomed (35.4%). No sign of synchronous diving was detected. Average maximum water temperature was 27.5 ± 0.9°C (Figure S8).


Group foraging in Socotra cormorants: A biologging approach to the study of a complex behavior
Diving behavior of Socotra cormorants. (a) Relationship between dive duration and maximum dive depth (black circles, y = 2.20x + 8.84, R2 = .69, P < .0001, n = 5,225) and frequency distribution of dive depth (gray vertical bars, n = 5,225). (b) Relationship between dive duration/postdive interval (PDI) and dive duration (black circles, y = 4.11ea, R2 = .06, P < .0001, n = 5,205) and frequency distribution of dive duration (gray vertical bars, n = 5,225)
© Copyright Policy - creativeCommonsBy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5383476&req=5

ece32750-fig-0008: Diving behavior of Socotra cormorants. (a) Relationship between dive duration and maximum dive depth (black circles, y = 2.20x + 8.84, R2 = .69, P < .0001, n = 5,225) and frequency distribution of dive depth (gray vertical bars, n = 5,225). (b) Relationship between dive duration/postdive interval (PDI) and dive duration (black circles, y = 4.11ea, R2 = .06, P < .0001, n = 5,205) and frequency distribution of dive duration (gray vertical bars, n = 5,225)
Mentions: Dive parameters are summarized in Table 2. Birds dived to shallow depths, with 22% and 92% of dives carried out to depths ≤2 and 15 m, respectively (Figure 8a). Accordingly, dive durations were short, with 67% of dives ≤30 s and 93% ≤45 s (Figure 8b). Dive duration increased linearly with maximum dive depth (Figure 8a). Frequency distribution of dive durations peaked for dives lasting 15–30 s and then decreased. Concomitantly, the dive duration/postdive interval ratio peaked for dives lasting 15–30 s, before decreasing (Figure 8b). Birds therefore favored a diving behavior that maximized the proportion of time spent underwater relative to the proportion spent at the surface. Dive profiles were parabolic (9.1%), V‐shaped (27.2%), irregular (28.2%), and flat‐bottomed (35.4%). No sign of synchronous diving was detected. Average maximum water temperature was 27.5 ± 0.9°C (Figure S8).

View Article: PubMed Central - PubMed

ABSTRACT

Group foraging contradicts classic ecological theory because intraspecific competition normally increases with aggregation. Hence, there should be evolutionary benefits to group foraging. The study of group foraging in the field remains challenging however, because of the large number of individuals involved and the remoteness of the interactions to the observer. Biologging represents a cost&#8208;effective solution to these methodological issues. By deploying GPS and temperature&ndash;depth loggers on individuals over a period of several consecutive days, we investigated intraspecific foraging interactions in the Socotra cormorant Phalacrocorax nigrogularis, a threatened colonial seabird endemic to the Arabian Peninsula. In particular, we examined how closely birds from the same colony associated with each other spatially when they were at sea at the same time and the distance between foraging dives at different periods of the day. Results show that the position of different birds overlapped substantially, all birds targeting the same general foraging grounds throughout the day, likely following the same school of fish. There were as many as 44,500 birds within the foraging flock at sea at any time (50% of the colony), and flocking density was high, with distance between birds ranging from 8 to 1,380&nbsp;m. Birds adopted a diving strategy maximizing time spent underwater relative to surface time, resulting in up to 72% of birds underwater in potential contact with prey at all times while foraging. Our data suggest that the benefits of group foraging outweigh the costs of intense aggregation in this seabird. Prey detection and information transmission are facilitated in large groups. Once discovered, shoaling prey are concentrated under the effect of the multitude. Fish school cohesiveness is then disorganized by continuous attacks of diving birds to facilitate prey capture. Decreasing population size could pose a risk to the persistence of threatened seabirds where group size is important for foraging success.

No MeSH data available.