African Penguins Spheniscus demersus, Bait Balls and the Allee Effect

Article (PDF Available)inArdea -Wageningen- 100(1) · April 2012with 348 Reads 
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
DOI: 10.5253/078.100.0113
Cite this publication
Abstract
We report co-operative group foraging in the African Penguin Spheniscus demersus. Groups of approximately 25–165 African Penguins were observed circling schools of pelagic fish, sometimes forcing them to the surface. During this behaviour 66–75% of penguins were underwater at any given time. Smaller numbers of African Penguins also joined foraging groups of Cape Gannets Morus capensis and Cape Cormorants Phalacrocorax capensis, but did not appear to corral fish schools when outnumbered by these species. African Penguins are listed as Endangered due to ongoing rapid population decreases. If group foraging confers an advantage to African Penguins, their dwindling populations may suffer from an Allee effect as colonies become too small to support sufficient densities of birds for foraging groups to form.
The population of African Penguins Spheniscus demer-
sus has fallen dramatically over the last decade
(Crawford et al. 2011) and the species recently has
been uplisted from Vulnerable to Endangered (BirdLife
International 2010). The most plausible explanation
for the recent collapse is a decrease in the availability of
small pelagic fish, their preferred prey, particularly in
the vicinity of breeding colonies (Pichegru et al. 2010,
Crawford et al. 2011). Despite numerous investigations
of their foraging ecology (e.g. Wilson 1985, Wilson &
Wilson 1995, Petersen et al. 2006, Ryan et al. 2007),
little is known about how African Penguins locate and
capture their prey (although they may use scent to
select productive areas at a coarse spatial scale; Wright
et al. 2011). Based on the position of bite marks on fish
(Wilson & Duffy 1986) and observations of groups of
penguins circling schools of pelagic fish (Wilson et al.
1987), Rory Wilson inferred that at least some African
Penguin foraging is cooperative, herding preferred prey
into dense schools, then striking from below. Their
conspicuously striped adult plumage appears to
promote dense, defensive schooling of small pelagic
fish, creating so-called ‘bait balls’ that are easier to
exploit (Wilson et al. 1987). However, it is unclear how
often this behaviour occurs, or how large a group is
required to corral a school of fish effectively.
Cooperative hunting is one of the classic mecha-
nisms underpinning an Allee effect, whereby the
growth rate of a small population decreases with popu-
lation size (inverse density dependence; Courchamp et
al. 1999). Simplistically, as a population’s size dwindles,
there are too few individuals to allow effective coopera-
tive hunting. This effect has not been explored in
African Penguins, largely because of the paucity of
empirical data on their cooperative foraging behaviour.
Wilson et al. (1986) argued that African Penguins do
not forage in groups of more than 20 birds, because
they cannot synchronise their diving. However, we
present observations of several hundred African
Penguins foraging together, suggesting that Allee
effects linked to cooperative hunting may be an issue in
larger populations than previously thought.
Short notes
African Penguins Spheniscus demersus, bait balls
and the Allee effect
Peter G. Ryan1,*, Lloyd Edwards2& Lorien Pichegru1
Ryan P.G., Edwards L. & Pichegru L. 2012. African Penguins Spheniscus
demersus, bait balls and the Allee effect. Ardea 100: 89–94.
We report co-operative group foraging in the African Penguin Spheniscus
demersus. Groups of approximately 25–165 African Penguins were observed
circling schools of pelagic fish, sometimes forcing them to the surface. During
this behaviour 66–75% of penguins were underwater at any given time. Smaller
numbers of African Penguins also joined foraging groups of Cape Gannets
Morus capensis and Cape Cormorants Phalacrocorax capensis, but did not
appear to corral fish schools when outnumbered by these species. African
Penguins are listed as Endangered due to ongoing rapid population decreases.
If group foraging confers an advantage to African Penguins, their dwindling
populations may suffer from an Allee effect as colonies become too small to
support sufficient densities of birds for foraging groups to form.
Key words: group foraging, Benguela, anchovy, sardine, predation
1Percy FitzPatrick Institute of African Ornithology, DST/NRF Centre of
Excellence, University of Cape Town, Rondebosch 7701, South Africa;
2Raggy Charters, P.O. Box 15317, Emerald Hill, Port Elizabeth 6011, South
Africa;
*corresponding author (pryan31@gmail.com)
ARDEA 100(1), 2012
90
Methods
African Penguins breed at two island groups in Nelson
Mandela Bay, Eastern Cape South Africa: St Croix and
Bird Islands. Together, these islands currently support
more than a third of all African Penguins, with St Croix
being home to the largest single colony (Crawford et al.
2011). Raggy Charters has been running small boat
tours to view marine mammals and seabirds in Nelson
Mandela Bay since 2002. Foraging groups of seabirds
often are investigated during these tours, and some of
these aggregations have been photographed by LE. We
searched this photographic archive for groups contain-
ing African Penguins. Multiple images were available
for each foraging group. We identified the birds and
counted the numbers of each species in each image.
The maximum count for each species was taken as a
minimum estimate of numbers of birds in a given forag-
ing group. We could also estimate the minimum dura-
tion of a foraging event, although most groups are only
spotted after they form, and it was not always possible
to remain with a foraging group for the duration of the
foraging event. Spearman rank correlations were used
to test for relationships between group size and dura-
tion. In some instances there were images of the forag-
ing group after foraging ceased, when most penguins
were resting on the surface. By comparing the number
of birds present in these images we estimated the
proportion of birds on the surface compared to those
underwater when foraging. Similar correction factors
could not be obtained for cormorants or gannets, as
some depart the area before foraging ceases.
Results
Thirteen foraging groups involving African Penguins
were photographed (n=95 images) from 2003 to
2010, mainly in summer (October–March), outside the
African Penguin’s peak breeding period. Water clarity
was reasonably good on most occasions, but sampling
was not random because the small boat tours only run
during relatively calm conditions. Eight aggregations
involved penguins swimming in a clearly defined circle
3–10 m in diameter (Figure 1A). That the penguins
were circling small pelagic fish was evident in at least
two cases, because a dense school of fish (presumably
Anchovy Engraulis capensis) was brought to the surface
(Figure 1B). Penguins were the dominant species in all
these foraging groups, but they often attracted large
numbers of terns, especially Common Terns Sterna
hirundo (Table 1), which were able to exploit the fish
by surface dipping. Penguin orientation on surfacing
was random in the other five foraging groups, suggest-
ing that they were not co-ordinating their foraging
effort. These groups contained larger numbers of Cape
Gannets Morus capensis (n=3, 15–25 individuals) or
Cape Cormorants Phalacrocorax capensis (n=2, 25–50
individuals), which may have prevented the African
Penguins from forming a tight, circling group. Fewer
African Penguins attended these foraging aggregations
than those where circling behaviour was observed
(Table 1). Gulls attended both types of aggregations.
Kelp Gulls Larus dominicanus were more abundant at
mixed-species aggregations whereas Grey-headed Gulls
Chroicocephalus cirrocephalus were more frequent at
penguin-dominated feeding groups (Table 1), although
this may have been influenced by the location of forag-
ing groups, as Grey-headed Gulls tend to remain close
to shore.
Numbers of penguins, cormorants and gannets
reported in Table 1 are minimum estimates, because
some individuals were underwater when the photo-
graphs were taken. In four instances a group was
followed until foraging ceased, whereupon most if not
all penguins rested on the water surface. In all four
cases the maximum number of penguins counted on
the surface was 3–4 times (average 3.5 ± 0.5) that
when they were foraging (Figure 2). This implies that
the average group size of penguins feeding in penguin-
dominated groups is around 150 individuals, compared
to an average of only 45 penguins in mixed-species
aggregations. The smallest circling group of penguins
photographed had 8 birds on the surface, suggesting
that 25–30 birds are required to corral a school of fish.
Species Penguins circle prey Random orientation
(n= 8) (n= 5)
Mean ± SD (range) Mean ± SD (range)
African Penguin
a
43.6 ± 33.3 (8–92) 13.0 ± 9.7 (3–26)
Cape Gannet 0.3 ± 0.7 (0–2) 12.0 ± 11.5 (0–25)
Cape Cormorant 3.8 ± 4.1 (1–10) 18.4 ± 20.4 (0–50)
Kelp Gull 3.6 ± 4.3 (0–10) 23.8 ± 20.8 (1–50)
Grey-headed Gull 1.3 ± 3.5 (0–10) 0.2 ± 0.4 (0–1)
Terns
b
39.8 ± 44.6 (0–105) 20.4 ± 24.0 (0–60)
All birds 92.4 ± 44.4 (23–138) 87.8 ± 37.0 (50–137)
aExcludes post-foraging counts of some groups which indicate the
total number of penguins is 3–4 times greater than the number at the
surface during foraging.
b89% Common Terns Sterna hirundo, 11% Swift Terns Thalasseus
bergii, and <1% Sandwich Terns T. sandvicensis.
Table 1. Minimum numbers of birds in foraging groups contain-
ing African Penguins in Nelson Mandela Bay, Eastern Cape,
South Africa. Two types of groups were recorded: those where
penguins surfaced in a coherent direction, apparently circling
their prey, and those where orientation on surfacing was random.
Short notes 91
Figure 1. An African Penguin feeding group showing a clear clockwise circling pattern (top) and a smaller group (bottom) that has
driven a bait ball of small fish right to the surface (visible as a silver mass in the centre of the picture). Photos by Lloyd Edwards.
ARDEA 100(1), 2012
92
Figure 2. African Penguins circling a school of fish (top) and 2 min later (bottom) after foraging activity ceased, showing roughly
three times as many birds resting on the surface (at least 158) than visible while foraging (c. 50). Photos by Lloyd Edwards.
Short notes
Foraging events lasted at least 5.4 ± 4.6 min, with no
difference between penguin-dominated groups (5.7
min, range 2–14 min) and mixed-species groups (5.0
min, range 1–12 min). There was no relationship
between penguin group size and foraging duration
(r
s
=0.512, n=11, P> 0.1) but larger groups foraged
for longer when all species were combined (r
s
=0.618,
n=11, P=0.05).
Discussion
The number of foraging groups photographed is rather
small, and there may be a bias towards larger groups
because they are more conspicuous. However, it is clear
that African Penguins forage in larger groups than
reported previously (Wilson et al. 1986) and that
synchronised diving is not a prerequisite for group
foraging (contra Wilson et al. 1986) as 25–33% of
penguins are on the surface at any time during these
foraging events. Species composition of the foraging
groups appears to influence penguin behaviour, with
penguins circling fish schools when they are the domi-
nant deep-diving species, but seemingly not doing so
when there are large numbers of other diving species
(Cape Gannets and Cape Cormorants). It is plausible
that the presence of large numbers of other diving birds
disrupts the penguins’ ability to effectively corral a fish
school; underwater observations are required to
confirm this speculation. A similar situation was
witnessed at the Snares Islands, New Zealand, where
Sooty Shearwaters Puffinus griseus displaced Antarctic
Terns Sterna vittata from crustacean swarms through
physical interference (Sagar & Sagar 1989).
Our observations show that African Penguins forage
in large groups at least occasionally, despite their
current small population size. It must be increasingly
difficult to form such groups as colony sizes decrease
(Crawford et al. 2001, 2011) and their foraging ranges
while breeding increase (Pichegru et al. 2010). Acting
in concert, these two factors greatly reduce the density
of penguins at sea around breeding islands. Whether a
decrease in group foraging behaviour results in an Allee
effect depends on whether it is more profitable to
forage in large groups than singly or in small groups.
Although such data currently are unavailable for
African Penguins, it seems plausible that group forag-
ing does enhance the rate of prey capture. Many
seabirds are primarily group foragers, and their individ-
ual foraging success improves with increasing group
size (Götmark et al. 1986). By working together,
seabirds targetting fish schools benefit by disrupting
the cohesiveness of predator avoidance tactics (Shealer
2002; see also Wilson et al. 1987).
If large group foraging is more rewarding for
African Penguins, the strength of the Allee effect will be
related in part to the frequency with which such forag-
ing occurs. Observations at sea off the Western Cape of
South Africa in the 1980s suggest that most penguins
forage singly or in small groups (<5 birds; Wilson et al.
1988). Whether this has changed as the population of
African Penguins has decreased is uncertain. The earli-
est observations of penguin group sizes at sea occurred
in the 1950s, when the population had already decreas-
ed substantially, and there was no decrease in the size
of penguin groups at sea between 1954–74 and the
1980s, despite the regional population of African
Penguins more than halving over this period (Wilson et
al. 1988). Current data on penguin group sizes at sea
would be useful to compare with previous estimates. At
face value, the fact that group size at sea remained
unchanged from the 1950s to the 1980s suggests that
group foraging is not very important for African
Penguins. However, penguin-mounted cameras reveal-
ed that Chinstrap Penguins Pygoscelis antarctica forage
in groups more often than previously thought (Takashi
et al. 2004). It should be feasible to infer the impor-
tance of penguin-dominated group foraging by equip-
ping African Penguins with dead reckoning loggers to
detect how often they undertake circling activity.
However, it is inevitable that foraging in large groups
will become increasingly difficult for birds in very small
colonies (<50 pairs), potentially increasing their risk of
local extinction (Crawford et al. 2001).
93
References
BirdLife International 2010. Threatened birds of the world.
www.birdlife.org.
Courchamp F., Clutton-Brock T. & Grenfell B. 1999. Inverse
density dependence and the Allee effect. Trends Ecol. Evol.
14: 405–410.
Crawford R.J.M., David J.H.M., Shannon L.J., Kemper J., Klages
N.T.W., Roux J.-P., Underhill L.G., Ward V.L., Williams A.J. &
Wolfaardt A.C. 2001. African penguins as predators and
prey – coping (or not) with change. Afr. J. Mar. Sci. 23:
435–447.
Crawford R.J.M., Altwegg R., Barham B.J., Barham P.J., Durant
J.M., Dyer B.M., Makhado A.B., Pichegru L., Ryan P.G.,
Underhill L.G., Upfold L., Visagie J., Waller L.J. &
Whittington P.A. 2011. Collapse of South Africa’s penguins
in the early 21st century: a consideration of food availabili-
ty. Afr. J. Mar. Sci. 33: 139–156.
Götmark F., Winkler D.W. & Andersson M. 1986. Flock-feeding
on fish schools increases individual success in gulls. Nature
319: 589–591.
Petersen S.L., Ryan P.G. & Grémillet D. 2006. Is food availability
limiting African Penguins at Boulders Beach? A comparison
of foraging ecology at mainland and island colonies. Ibis
148: 14–26.
ARDEA 100(1), 2012
94
Pichegru L., Grémillet D., Crawford R.J.M., & Ryan P.G. 2010.
Marine no-take zone rapidly benefits threatened penguin.
Biol. Letters 6: 498–501.
Ryan P.G., Petersen S.L., Simeone A. & Grémillet D. 2007.
Diving behaviour of African Penguins: do they differ from
other Spheniscus penguins? Afr. J. Mar. Sci. 29: 153–160.
Sagar P.M. & Sagar J.L. 1989. The effects of wind and sea on the
feeding of Antarctic Terns at the Snares Islands, New
Zealand. Notornis 36: 171–182.
Shealer D.A. 2002. Foraging behavior and food of seabirds. In
Schreiber E.A. & Burger J. (eds) Biology of Marine Birds.
CRC Press, Boca Raton, pp. 217–262.
Takashi A., Sato K., Naito Y., Dunn M.J., Trathan P.N. & Croxall
J.P. 2004. Penguin-mounted cameras glimpse underwater
group behaviour. Proc. R. Soc. Lond. B 271: S281–S282.
Wilson R.P. 1985. The Jackass Penguin (Spheniscus demersus) as
a pelagic predator. Mar. Ecol. Progr. Ser. 25: 219–227.
Wilson R.P. & Duffy D.C. 1986. Prey seizing in African Penguins
Spheniscus demersus. Ardea 74: 211–214.
Wilson R.P. & Wilson M-P.T. 1995. The foraging behaviour of the
African Penguin Spheniscus demersus. In Dann P., Norman I.
& Reilly P. (eds) The Penguins Surrey Beatty & Sons,
Chipping Norton, pp. 244–265.
Wilson R.P., Wilson M-P.T. & McQuaid L. 1986. Group size in
foraging African Penguins (Spheniscus demersus). Ethology
72: 338–341.
Wilson R.P., Ryan P.G., James A. & Wilson M.-P. 1987. Conspi-
cuous coloration may enhance prey capture in some pisci-
vores. Anim. Behav. 35: 1558–1560.
Wilson R.P., Wilson M-P.T. & Duffy D.C. 1988. Contemporary
and historical patterns of African Penguin Spheniscus demer-
sus: distribution at sea. Estuar. Coast. Shelf Sci. 26:
447–458.
Wright K.L.B., Pichegru L. & Ryan P.G. 2011. Penguins are
attracted to dimethyl sulphide at sea. J. Exp. Biol. 214:
2509–2511.
Samenvatting
Dit artikel beschrijft het foerageergedrag van Afrikaanse
Pinguïns Spheniscus demersus voor de kust van Zuid-Afrika.
Tijdens het onderzoek zocht de soort voedsel in groepen van
25–165 vogels, waarbij grote scholen vis ingesloten werden. De
pinguïns verbleven dan lange tijd onder water: op enig moment
waren niet meer dan 25–33% van de vogels aan het waterop-
pervlak zichtbaar. Ook sloten de pinguïns zich aan bij groepen
voedselzoekende Kaapse Jan van Genten Morus capensis en
Kaapse Aalscholvers Phalacrocorax capensis. De aantallen waren
dan wel kleiner en de vogels dreven de visscholen niet op. De
populatie van de Afrikaanse Pinguïn neemt snel in omvang af en
heeft tegenwoordig de status van een bedreigde soort.
Aannemende dat de pinguïns baat hebben bij groepsgewijs
voedsel zoeken, dan zou de populatie te lijden kunnen krijgen
van het zogeheten Allee-effect: het (foerageer)succes van indivi-
duen neemt af naarmate de populatie kleiner wordt. De dicht-
heid aan pinguïns is dan te laag om voldoende grote groepen
tijdens het vissen te kunnen vormen. (JP)
Corresponding editor: Jouke Prop
Received 9 November 2011; accepted 30 January 2012
  • ... Vocalizations of this species at sea have been conjectured to be associated with foraging opportunities and anti-predator behaviour, such as porpoising (Davies 1956, Siegfried et al. 1975. African Penguins engage in group foraging, herding schooling fish into aggregations that improve foraging efficiency (Ryan et al. 2012, McInnes et al. 2017. Fish-herding behaviour is extremely rare among birds (exceptions include American White Pelicans Pelecanus erythrorhynchos, McMahon & Evans 1992) but is commonly utilized as a foraging strategy by delphinids (Leatherwood 1975, Gallo-Reynoso 1991, Simil€ a 1997, Benoit-Bird & Au 2009). ...
    ... The function of calling behaviour at sea may differ between penguin species according to their degree of foraging specialization and the types of dominant prey targeted. The results of this study further highlight the importance of social behaviour to the survival of African Penguins and the need to be cognisant of potential Allee effects (Allee 1938, Courchamp et al. 1999) that may already be operating on this threatened species (Ryan et al. 2012, McInnes et al. 2017. ...
    Article
    Social cohesion and prey location in seabirds are largely enabled through visual and olfactory signals, but these behavioural aspects could potentially also be enhanced through acoustic transfer of information. Should this be the case, calling behaviour could be influenced by different social‐ecological stimuli. African Penguins Spheniscus demersus were equipped with animal‐born video recorders to determine if the frequency and types of calls emitted at sea were dependent on behavioural modes (commuting, sedentary and dive bout) and social status (solitary versus group). For foraging dive bouts we assessed whether the timing and frequency of calls were significantly different in the presence of schooling prey versus single fish. The probability of call events were significantly more likely for birds commuting early and late in the day (for solitary birds) and during dive bouts (for groups). During foraging dive bouts the frequency of calls was significantly greater for birds diving in the presence of schooling fish and birds called sooner after a catch in these foraging scenarios compared to when only single fish were encountered. Three call types were recorded, 'flat', 'modulated' and 'two‐voices' calls but there was no significant relationship detected with these call types and behavioural modes for solitary birds and birds in groups. Results of this study show that acoustic signalling by African Penguins at sea is used in a variety of behavioural contexts and that increased calling activity in the presence of more profitable prey could be of crucial importance to seabirds that benefit from group foraging.
  • ... Synchrony of arrival, such that many individuals arrive in a short time window, is often sign that individuals actively forage in groups (Krebs 1974;Bayer 1981;Burger 1997;Elliott et al. 2009). These groups can be formed via information exchange, with unsuccessful birds following successful ones (information center hypothesis- Ward and Zahavi 1973;Brown 1986;Buckley 1997b;Campobello and Hare 2007), through enhanced detection of prey when in groups (network foraging- Wittenberger and Hunt 1985;Mock et al. 1988) or through synchronised attack on fish schools (cooperative hunting -Bednarz 1988;Ryan et al. 2012, Sutton et al. 2015. Therefore, we hypothesised that individuals feeding on schooling fish would come back to the colony to feed their chick more synchronised in time (i.e., displaying more temporal aggregation) than those feeding on solitary prey. ...
    ... At a small spatial scale, camera loggers detected several very close encounters of foraging conspecifics (< 4 m), more than what would be predicted by chance even in the context of spatial aggregation. However, in 7 h of active foraging over 16 birds, we did not observe cooperative hunting, which is displayed in species like the African penguin (Eudyptula minor), where several individuals circle around fish schools to prevent them from fleeing (Ryan et al. 2012). Furthermore, capelin seemed to be loosely aggregated, rather occurring in dense schools. ...
    Article
    Full-text available
    Analyzing how animals are distributed in space and time is important to understand the behavioural interactions that underlie population dynamics, especially for highly social species. Thick-billed murres (Uria lomvia) breed in some of the largest and densest colonies of any seabird. Although this bird is known to aggregate at sea, little is known about when, where, and why the birds form aggregations. We examined the spatial and temporal patterns of foraging aggregations during the breeding season through various scales via (1) measurement of the synchrony of arrivals of adults feeding their chicks at the colony, and (2) use of both GPS and camera loggers attached on the birds to examine the proximity of birds at sea. Adult arrivals at the colony were synchronised when bringing capelin (Mallotus villosus), a gregarious pelagic fish, but not when bringing sculpin (primarily Triglops spp.), a solitary benthic fish. Camera loggers revealed very close encounters of foraging conspecific (< 4 m), much closer than what was predicted by chance, despite low prey densities. GPS loggers also showed diffuse at-sea aggregations with minimal distances closer than expected by chance. However, those study birds did not typically share foraging trajectories. We suggest that, at smaller scales, murres form tight groups to increase searching efficiency underwater. At larger scales, murre aggregations are most likely a result of foraging individuals converging in the more prolific areas, either by independently encountering prey hotspots, or by cueing on other foraging birds.
  • ... Within-group responsiveness provides important benefits for individual group members, allowing for cohesion and consensus to form in movement decisions [2,16], predator avoidance [17] and resource exploitation [18]. In addition, wild penguins have exhibited within-group synchrony: rockhopper (Eudyptes chrysocome) and Adélie (Pygoscelis adeliae) penguins synchronized their diving to increase fishing success [19], and cooperative foraging has been reported for African penguins (Spheniscus demersus) [20], while little penguins (Eudyptula minor) display group behavior arriving at the colony and departing to sea, as a predator avoidance strategy [18]. What about captivity? ...
    Article
    Full-text available
    Understanding animal personalities has notable implications in the ecology and evolution of animal behavior, but personality studies can also be useful in optimizing animal management, with the aim of improving health and well-being, and optimizing reproductive success, a fundamental factor in the species threatened with extinction. Modern zoos are increasingly being structured with enclosures that host different species, which permanently share spaces. This condition has undeniable positive aspects, but, in some species, it could determine the appearance of collective or synchronized behaviors. The aim of this study was to verify, in a colony of three species of communally housed penguins (Pygoscelis papua, Aptenodytes patagonicus and Eudyptes moseleyi), through a trait-rating assessment, if interspecific group life impacts on the expression of personality traits, and if it is possible to highlight specie-specific expression of personality traits, despite the influence of forced cohabitation. For many of the personality traits we analyzed, we have observed that it was possible to detect an expression that differed, according to the species. From a practical point of view, these data could ameliorate the management of the animals, allowing to design animal life routines, according to the different behavioral characteristics of the cohabiting species.
  • ... They frequently dive to more than 30 m [6] and can herd schools of fish from these depths into shallow waters [7]. Volant seabirds such as gulls and terns are attracted to groups of surfacing African penguins and have been observed feeding on small fish in these situations [8]. We investigated the potential mechanisms of facilitation between African penguins and volant seabirds from an in situ perspective by analysing footage of animal-borne video recorders (AVRs) deployed on breeding African penguins at Stony Point, South Africa. ...
    Article
    Full-text available
    Visual and olfactory signals are commonly used by seabirds to locate prey in the horizontal domain, but foraging success depends on prey depth and the seabird's ability to access it. Facilitation by diving seabirds has long been hypothesized as a mechanism to elevate deep prey to regions more accessible to volant seabirds, but this has never been demonstrated empirically. Footage from animal-borne video loggers deployed on African penguins was analysed to establish if volant seabird encounters involved active cuing by seabirds on penguins to obtain prey and, during mutual prey encounters, if interactions were driven by the vertical displacement of prey by penguins. Independent of prey biomass estimates, we found a strong inverse relationship between penguin group size, a proxy for visibility, and the time elapsed from the start of penguins' dive bouts to their first encounter with other seabirds. Most mutual prey encounters (7 of 10) involved schooling prey elevated from depths greater than 33 m by penguins and only pursued by other seabird species once prey was herded into shallow waters. This is likely to enhance foraging efficiency in volant seabird species. As such, penguins may be integral to important processes that influence the structure and integrity of marine communities.
  • ... As a consequence, species from all seabird orders commonly gather at sites where prey resources are concentrated, most often in multi-species associations (Siegfried et al. 1975, Hoffman et al. 1981, Harrison et al. 1991, Camphuysen and Webb 1999, Clua and Grosvalet 2001. In this context, individuals may benefit from group foraging (Ryan et al. 2012, Lett et al. 2014, Thiebault et al. 2015, McInnes et al. 2017) and use both visual and acoustic cues (Thiebault et al. 2014b(Thiebault et al. , 2016. Despite numerous descriptions of seabird aggregations (mainly from boat observations), studies addressing the mechanisms involved in their social interactions at sea have long been constrained by technical limitations. ...
    Article
    Seabirds spend most of their time at sea, yet our knowledge of their activities and behaviour is limited due to difficulties of in‐situ data collection. In particular, we know virtually nothing about their acoustic communication when at sea. We benefited from the recent development of miniaturised audio‐recording devices to deployacoustic recorders on breeding Cape gannets Morus capensis to study their vocal activity while foraging. Call sequences were recorded on 1718 occasions, from which acoustic variables were measured on calls with good recording quality. A total of 1348 calls from 18 birds were measured in temporal and frequency domains. Each call was assigned to a behavioural context defined acoustically: sitting on the water, flying, taking off or just before diving. Potential discrimination among calls from different contexts was tested using the random forest algorithm. Within each context, individual stereotypy in the calls was assessed per acoustic variable using a measure of potential of individual coding, and as a combination of variables using a similar multivariate analysis. The acoustic structure differed according to the behavioural context (global accuracy of prediction 75 %). Temporal variables (sequence and call duration sequence and ) were most important to correctly classify the calls among the four contexts. When considering only two contexts, on the water and in the air (merging flying and diving), frequency and spectral variables (percentage of energy below 1200 Hz and fundamental frequency) were of most importance (accuracy 86 %). A combination of acoustic variables was necessary to discriminate individuals, but calls from all contexts were not strongly individually distinct (accuracy 41 % ‐ 63 %). We provided the first detailed acoustic analysis of a foraging seabird and demonstrated context‐specific acoustic structure in its vocalisations at sea. Our results suggest that seabirds use vocal communication to exchange various types of information that likely improves foraging success. This article is protected by copyright. All rights reserved.
  • ... Social foraging can increase prey detection and capture in several species of seabirds through cooperative hunting. For instance, penguin species can cooperatively corral fish shoals [27] and perform synchronised dives (e.g. [28]), which may increase prey detection and/or capture as well as provide group protection through synchronization. ...
    Article
    Social foraging behaviours, which range from cooperative hunting to local enhancement, can result in increased prey capture and access to information, which may significantly reduce time and energy costs of acquiring prey. In colonial species, it has been proposed that the colony itself may act as a site of social information transfer and group formation. However, conclusive evidence from empirical studies is lacking. In particular, most studies in colonial species have generally focussed on behaviours either at the colony or at foraging sites in isolation, and have failed to directly connect social associations at the colony to social foraging. In this study, we simultaneously tracked 85% of a population of Australasian gannets (Morus serrator) over multiple foraging trips, to study social associations at the colony and test whether these associations influence the location of foraging sites. We found that gannets positively associate with conspecifics while departing from the colony and that co-departing gannets have more similar initial foraging patches than individuals that did not associate at the colony. These results provide strong evidence for the theory that the colony may provide a source of information that influences foraging location.
  • ... During the day, redeye schools descend into deeper water [12], but their presence in the tern's diet may be explained by the fact that juvenile fish are found near the surface in inshore waters where they form mixed schools with anchovy and juvenile sardine [51]. In addition, other predators such as African penguins or dolphins, may force redeyes and other mid-water species, such as lantern fish Lampanyctodes hectorus, to the surface, making them available to terns [52,53]. Atlantic saury were particularly abundant in the diet when adults were provisioning fledglings, as observed in Cape gannets [5] and roseate terns Sterna dougalli in the Azores [54]. ...
    Article
    Full-text available
    Marine predators, such as seabirds, are useful indicators of marine ecosystem functioning. In particular, seabird diet may reflect variability in food-web composition due to natural or human-induced environmental change. Diet monitoring programmes, which sample diet non-invasively, are valuable aids to conservation and management decision-making. We investigated the diet of an increasing population of greater crested terns Thalasseus bergii in the Western Cape, South Africa, during three successive breeding seasons (2013 to 2015), when populations of other seabirds feeding on small pelagic schooling fish in the region were decreasing. Breeding greater crested terns carry prey in their bills, so we used an intensive photo-sampling method to record their diet with little disturbance. We identified 24,607 prey items from at least 47 different families, with 34 new prey species recorded. Fish dominated the diet, constituting 94% of prey by number, followed by cephalopods (3%), crustaceans (2%) and insects (1%). The terns mainly targeted surface-schooling Clupeiformes, with anchovy Engraulis encrasicolus the most abundant prey in all three breeding seasons (65% overall). Prey composition differed significantly between breeding stages and years, with anchovy most abundant at the start of the breeding season, becoming less frequent as the season progressed. The proportion of anchovy in the diet also was influenced by environmental factors; anchovy occurred more frequently with increasing wind speeds and was scarce on foggy days, presumably because terns rely in part on social facilitation to locate anchovy schools. The application of this intensive and non-invasive photo-sampling method revealed an important degree of foraging plasticity for this seabird within a context of locally reduced food availability, suggesting that, unlike species that specialise on a few high-quality prey, opportunistic seabirds may be better able to cope with reductions in the abundance of their preferred prey.
  • Chapter
    This chapter presents a detailed guide to hand‐rearing techniques for raising African penguins. It provides valuable information on record keeping, appropriate intervention, diet protocol, housing, feeding procedures, and care and stabilization criteria considered throughout the hand‐rearing process. The chapter also presents common medical problems encountered in the African penguins and appropriate solutions. In addition, it provides information on the processes involved in preparing the African penguins for wild release.
  • Article
    Full-text available
    Seismic surveys in search for oil or gas under the seabed, produce the most intense man-made ocean noise with known impacts on invertebrates, fish and marine mammals. No evidence to date exists, however, about potential impacts on seabirds. Penguins may be expected to be particularly affected by loud underwater sounds, due to their largely aquatic existence. This study investigated the behavioural response of breeding endangered African Penguins Spheniscus demersus to seismic surveys within 100 km of their colony in South Africa, using a multi-year GPS tracking dataset. Penguins showed a strong avoidance of their preferred foraging areas during seismic activities, foraging significantly further from the survey vessel when in operation, while increasing their overall foraging effort. The birds reverted to normal behaviour when the operation ceased, although longer-term repercussions on hearing capacities cannot be precluded. The rapid industrialization of the oceans has increased levels of underwater anthropogenic noises globally, a growing concern for a wide range of taxa, now also including seabirds. African penguin numbers have decreased by 70% in the last 10 years, a strong motivation for precautionary management decisions, including the exclusion of seismic exploratory activities within at least 100 km of their breeding colonies.
  • Article
    The foraging behaviour of African penguins was studied in 10 birds at Dassen Island and 22 birds at Marcus Island, South Africa. Three foraging dive types were identified: 1) 'Search' dives where a constant heading was maintained and the birds descended the water column to a particular depth before returning immediately to the surface. Mean swim speed during the course of the dive was independent of maximum depth reached. 2) 'Feeding' dives where prey were encountered. Here dives were initiated in the same way as 'search' dives but changed when bird swim direction suddenly became erratic and speed varied between 0-3.5 m/sec. 3) 'Post-feeding' dives immediately followed 'feeding' dives and were characterized both by steep dive angles directed to the depth where food was previously ingested and a much more variable heading than birds executing 'search' dives.
  • Article
    Full-text available
    African penguins Spheniscus demersus live in the Benguela and western Agulhas ecosystems off southern Africa. Their numbers decreased throughout the 20th century from at least 1.5 million to about 0.18 million adults, although different regional trends were apparent. They feed to a large extent on shoaling epipelagic fish, notably anchovy Engraulis capensis and sardine Sardinops sagax, and regional trends in the abundance of penguins are associated with trends in the abundance and distribution of these prey fish. Many first-time breeders emigrate from colonies where feeding or other conditions at the time are unfavourable to more favourable breeding localities. This has led to both the extinction and formation of colonies. Food now may limit colonies at relatively small sizes, a fact attributable to industrial fisheries reducing the densities of forage fish. African penguins share their habitat with several other predators, with which they compete for food and breeding space. One of these, the Cape fur seal Arctocephalus p. pusillus, increased through the 20th century to 1.5 – 2 million animals at its close. Reported observations of predation by fur seals on seabirds have increased in recent decades and threaten the continued existence of small colonies of penguins. Stochastic modelling suggests that colonies of 10 000 pairs have a 9% probability of extinction in 100 years, so smaller populations should be regarded as "Vulnerable". However, in a period of prolonged food scarcity off southern Namibia, the regional population decreased from more than 40 000 pairs in 1956 to about 1 000 pairs in 2000, and many colonies numbering less than 1 000 pairs became extinct. The minimum viable population for African penguins is currently considered to be >40 000 pairs, likely of the order of 50 000 pairs, a figure equivalent to its level in 2000. The chance of survival of the species through the 21st century is tenuous.
  • Article
    Full-text available
    Line transects from boats were conducted during 1984 and 1985 to determine African Penguin (Speniscus demersus) distribution in the South African Cape waters. Range limits for breeding birds were derived from information on penguin travelling speeds and durations of foraging trips. Over 50% of all penguins considered to be non-breeding occurred within 20 km of the coast whilst over 50% of all breeding birds occurred within 3 km of the coast. Penguin density decreased with increasing distance offshore. The most frequently encountered penguin group size was one with larger groups decreasing in incidence according to a power curve decay. There was no difference in the frequency of occurrence of different group sizes between breeding and non-breeding penguins, nor did group size distribution change with distance offshore. Data on African Penguin distribution at sea collected in 1984 and 1985 was not discernably different to equivalent data collected between 1954 and 1974. The composition of penguin group size was also the same during both periods.
  • Article
    African penguins Spheniscus demersus closely resemble Magellanic S. magellanicus and Humboldt S. humboldti penguins and have similar breeding and feeding ecologies. Adults feed on pelagic schooling fish in continental shelf waters, but African penguins have been reported to have shallower dive angles and remain submerged longer for dives to a given depth than their congeners. The few data for African penguins were gathered using relatively large time-depth recorders. We measured diving behaviour of 36 African penguins provisioning small chicks at three colonies near Cape Town, South Africa. Maximum and mean dive depths were 69m and 14m respectively. Diving took place mainly during the day. Although dive depths differed between colonies, there were no significant differences in dive duration or maximum, median or mean depth. Total dive duration, descent time, bottom time, ascent time and dive angle all were strongly correlated with the maximum depth attained. The diving behaviour of African penguins is similar to that of its congeners. Diving performance probably was compromised by the data-logger used in the previous study. Comparative data from Humboldt penguins also indicate potential biases in an earlier study of this species. Care is needed when comparing the diving performance of penguins measured using different loggers.
  • Article
    Full-text available
    The number of African penguins Spheniscus demersus breeding in South Africa collapsed from about 56 000 pairs in 2001 to some 21 000 pairs in 2009, a loss of 35 000 pairs (>60%) in eight years. This reduced the global population to 26 000 pairs, when including Namibian breeders, and led to classification of the species as Endangered. In South Africa, penguins breed in two regions, the Western Cape and Algoa Bay (Eastern Cape), their breeding localities in these regions being separated by c. 600 km. Their main food is anchovy Engraulis encrasicolus and sardine Sardinops sagax, which are also the target of purse-seine fisheries. In Algoa Bay, numbers of African penguins halved from 21 000 pairs in 2001 to 10 000 pairs in 2003. In the Western Cape, numbers decreased from a mean of 35 000 pairs in 2001-2005 to 11 000 pairs in 2009. At Dassen Island, the annual survival rate of adult penguins decreased from 0.70 in 2002/2003 to 0.46 in 2006/2007; at Robben Island it decreased from 0.77 to 0.55 in the same period. In both the Western and Eastern Cape provinces, long-term trends in numbers of penguins breeding were significantly related to the combined biomass of anchovy and sardine off South Africa. However, recent decreases in the Western Cape were greater than expected given a continuing high abundance of anchovy. In this province, there was a south-east displacement of prey around 2000, which led to a mismatch in the distributions of prey and the western breeding localities of penguins.
  • Article
    Diving synchrony was examined for varying group sizes of African penguins (Spheniscus demersus) travelling to their foraging grounds from their breeding islands. Groups of fewer than 12 birds always dived synchronously, whereas groups of more than 17 birds always dived asynchronously. Since travelling penguins do not dive deeply, large groups of birds can remain together irrespective of diving synchronization. Observations from boats showed that foraging penguins rarely occurred in groups of more than 17 birds. We suggest that groups of penguins that do not have synchronized dives cannot forage effectively, because foraging penguins dive deeply.