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Some predators face the problem of locating and capturing foods while at the same time avoiding a number of environmental hazards and even predation on themselves. These challenges can be more extreme for some species than for others (Raubenheimer 2010). For example, a number of marine predators forage specifically within the air-water interface (Thewissen & Nummela 2008). The need to function in both media imposes major constraints, evolutionary pressures and physiological trade-offs on the individual's morphology, physiology and sensory systems (Kröger & Katzir 2008). It has been suggested that air-breathing marine animals physiologically prepare for dives of a specific depth by loading oxygen prior to submergence (Thompson & Fedak 2001). These animals include penguins, which also apparently prepare their dives before entering the water with the aim of increasing prey capture success (Wilson 2003). Australasian gannets (Morus serrator; hereafter gannets) are highly specialised marine predators that feed mainly on pelagic fish and squid at the air-water interface (Robertson 1992; Machovsky-Capuska et al. 2011a; Schuckard et al. 2012). Diving often occurs in multi-species-feeding associations (MSFA) that involve high densities of marine predators increasing competition for prey capture (Machovsky-Capuska et al. 2011 a, b). Gannets detect prey from the air and perform rapid plunge-dives to capture prey underwater using either U-or V-shaped dive profiles that have a significantly different level of prey capture success (95% vs. 43%, respectively, Machovsky-Capuska et al. 2011b; Machovsky-Capuska et al. 2012). We were therefore Notornis, 2013, Vol. 60: 255-257 0029-4470 © The Ornithological Society of New Zealand, Inc.
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255
Some predators face the problem of locating and
capturing foods while at the same time avoiding
a number of environmental hazards and even
predation on themselves. These challenges can
be more extreme for some species than for others
(Raubenheimer 2010). For example, a number
     
the air-water interface (Thewissen & Nummela
2008). The need to function in both media imposes
    
    
    
   
   
        

2001). These animals include penguins, which also
     
   
success (Wilson 2003).
Australasian gannets (Morus serrator; hereafter
     
         
    
et al.et al. 2012). Diving
often occurs in multi-species-feeding associations
(MSFA) that involve high densities of marine
   
( et al. 2011 a, b). Gannets

       
    
       
et al. 2011b;
et al. 2012). We were therefore
Notornis, 2013, Vol. 60: 255-257

Received 8 Mar 2013; accepted 17 May 2013
*Correspondence: g.machovsky@sydney.edu.au
SHORT NOTE
Can gannets (Morus serrator) select their diving prole prior to
submergence?
*










256
       
is determined prior to submergence, or whether it
       
phase of the dive.
       
        

of aerial video footage of gannet dive behaviour was

   Lagenorhynchus obscurus) feeding

underwater housing (for more details see Vaughn et
al. 2007; 2008). The dolphin feeding bout occurred

      
      


 

underwater momentum of the plunge and are short
in duration were categorised as V-shaped whereas
       
      
et al. (2011b). The angle

      
dives in the plane perpendicular to the camera
optical axis, using the water surface as the horizontal

       

version 11.0.2. For statistical comparisons, data
were tested using a t- test in PAWS Statistics version
18. We report data as mean ± SD.
        
water for a total of 25 dives showed that during
       
      
than during V-shaped dives (53.70 ± 7.30 degrees;
t-test, t = -3.84, df = 23, P < 0.001, Fig. 1). These
  
before the birds had entered the water, suggesting
that gannets might predict their dive performance
  
the aerial phase of the plunge dive as suggested
  et al. (2009). Among seabirds,
    
        
      et al. 1996;
 
dives in gentoo penguins (Pygoscelis papua) are used
to forage in suitable habitats, whereas V-shaped
       
et al.      

 

et al.


decisions that enable them to maximise the time

     
       
foraging (Aidala et al. 2012). Although gannets are

 et al. 2012) that are able to see in the

 et al. 2011c), it is still unclear how their

the air. Further studies are needed to understand the

in complex marine environments.
ACKNOWLEDGEMENTS
        
        
Department of Wildlife and Fisheries Sciences, Texas A&M
  
      
Marlborough District Council. D.R. and G.M.C. are

Fund.
LITERATURE CITED
Aidala,   J.; Fidler,
A.; Chong,  
M. G.; Talaba,       
      
lineages: paleognaths, parrots, and songbirds. Journal
of Comparative Physiology A 198: 495-510.
Fig. 1. Dive angles relative to the horizon during V-shaped
 Australasian gannets (Morus
serrator)
and error bars, which represent standard deviations.
Short note
257

  Sensory
evolution on the threshold: Adaptations in secondarily
aquatic vertebrates 
      

       
paradigm of ecological optics. Nature 293: 293-294.
      
    
     
diving in Gannets. Ibis 153: 631-635.
      
      
  Morus
serratorMarine
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     
       
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
    
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Encyclopedia of animal behaviour, Vol. 1.
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
       
      
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Journal of Ecology 16: 77-81.
      
    
(Morus serrator     
Notornis 59: 66-70.
        

  Berkeley, Los Angeles, London:
University of California Press, 358 pp.


Animal Behaviour
61: 287-296.
          
      Lagenorhynchus
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New Zealand Journal of Marine and Freshwater Research
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          
      
      
Journal of Mammalogy 89: 1051-1058.
 
Diving behaviour of gentoo penguins, (Pygoscelis
papuaMarine
Biology 126: 153-162.
       
Marine Ecology Progress Series 249: 305-310.
Keywords seabirds; Morus serrator; dive behaviour; dive

Short note
... The drone models are inspired by the Gannet bird because of their efficient performance with diving into water to catch prey (Raubenhelmer, 2013;Bhar et al., 2019;Ropert-Coudert et al., 2004). At the point of impact, when the head is underwater and the rest of the drone is not, the drone resembles closely to a beam subjected to an axial load. ...
... Weiss (Weiss) showed that a 3D cone can be an estimated representation of the Gannet in a streamlined position using computation fluid dynamics. Yang et al., 2012, 2013 investigated the direct effect the dive angle and initial velocity have on the force during water-entry using computational fluid dynamics. Wu et al. (2019) used a computer science algorithm to determine the forcing and diving trajectory. ...
Article
Many external sources of excitation can interfere with the performance of drones, such as propeller or flapping motion. This work investigates the effects external excitation plays on the nonlinear system's dynamics of Gannet-inspired drones. Using Euler-Bernoulli beam theory, the partial differential equations of motion are solved following the Hamilton's principle. Galerkin discretization is then applied to convert the equations of motion to ordinary differential equations in which to obtain an approximation for the nonlinear dynamic response before buckling occurs. The model is inspired by the Gannet bird, where the head is simplified to a cone shape, the neck is resembled by a soft beam, and the rest of the body is represented by a stiff, thicker beam to suggest a buckling behavior physical for the diving bird if buckling is to occur. The results observe the direct effects the external forcing, the damping, the impact velocity, and the boundary conditions have on the resonant frequency range and deflection. The results estimate that increasing the forcing amplitude will in turn amplify the hardening behavior and the maximum displacement. To maintain a lower forcing amplitude consistent with a reasonable external acceleration, a smaller drone mass should be employed. It is observed that higher damping should be applied to minimize the drone's nonlinear effects. The speed at which the drone impacts the water should be chosen to be lower than the estimated buckling speed to avoid lower natural frequencies and to reduce the hysteresis region in order to minimize the nonlinear behavior. From the boundary conditions explored, stiffer boundary conditions should be employed to increase the buckling speed and reduce the deflection when entering water.
... Biologists have previously focused on the diving behavior in terms of ecological factors, such as diving depths, prey species, and hunting success rate (8)(9)(10), and physiological features, such as the role of vision while crossing the air-water interface (11,12). Unique kinematic and morphological features during the dive have also been observed, such as having a sharp, arrow-like body posture and a straight, long, and slender neck (13,14). However, a mechanical understanding of plunge-diving birds is not well-established. ...
... The two main forms of plunge-diving observed are known as the V-shaped dive and the U-shaped dive (5). During V-shaped dives, the seabird impacts the surface at an angle, whereas during U-shaped dives the impact trajectory is more perpendicular to the surface (14,17). Although the mechanical forces may differ between the two dives, both U-shaped and Vshaped dives experience an axial force significantly larger than a transverse force. ...
Article
Full-text available
In nature, several seabirds (e.g., gannets and boobies) dive into water at up to 24 m/s as a hunting mechanism; furthermore, gannets and boobies have a slender neck, which is potentially the weakest part of the body under compression during high-speed impact. In this work, we investigate the stability of the bird’s neck during plunge-diving by understanding the interaction between the fluid forces acting on the head and the flexibility of the neck. First, we use a salvaged bird to identify plunge-diving phases. Anatomical features of the skull and neck were acquired to quantify the effect of beak geometry and neck musculature on the stability during a plunge-dive. Second, physical experiments using an elastic beam as a model for the neck attached to a skull-like cone revealed the limits for the stability of the neck during the bird’s dive as a function of impact velocity and geometric factors. We find that the neck length, neck muscles, and diving speed of the bird predominantly reduce the likelihood of injury during the plunge-dive. Finally, we use our results to discuss maximum diving speeds for humans to avoid injury.
... Ropert-Coudert et al [16] placed accelerometers on Gannets and noted that there was insignificant deceleration upon entry, allowing Gannets to reach greater depths more quickly while still conserving energy. Raubenhelmer [19] monitored the dives of Gannets with a video camera and concluded that Gannets choose their dive performance from flight. Considering the vertical axis as a reference, they enter the water at a larger angle for a shallow dive, and enter at a smaller angle for a deeper dive. ...
Article
A nonlinear model is proposed to answer at which diving speeds and beak angles will cause injury to Gannet-inspired beam systems during plunge-diving. In doing so, the critical velocities at which buckling occurs with various types of boundary conditions are first obtained for vertical dives and the resulting forces at the point of impact are determined. The Gannet-inspired system is modeled as an Euler-Bernoulli beam to represent the neck and body of the Gannet, while the head of the Gannet is modeled as a cone with varying half-angles. The experimental investigations of Gannet-like diving systems are first introduced to present the varying parameters and assumptions of the simplified model. Next, the resulting forces during impact are investigated and a study is conducted to compare various approximations of the drag coefficient for the cone-shaped head. Considering the mid-plane stretching nonlinearity, the equations of motion for the structural system under various types of boundary conditions are derived using the Hamilton's principle. The characteristic equations, buckled configurations, and critical velocities are determined for each set of boundary conditions. The results show that the system with the smallest half-beak angle and thus the lowest drag force and beam length delays the critical velocity and is most representative of a Gannet during diving. The obtained results demonstrate great agreement with the conducted experiments. For clamped-clamped boundary conditions, the critical velocity is found to be the greatest because of the increased stability at both ends of the beam. It is also noted that a nonlinear approximation for the coefficient of drag offers the best fit with the provided experimental values when compared to a hyperbolic tangent approximation, which predicts the coefficient of drag to be less than that obtained in experiments, and thus predicts that the systems will buckle at higher velocities.
... Ropert-Coudert et al [16] placed accelerometers on Gannets and noted that there was insignificant deceleration upon entry, allowing Gannets to reach greater depths more quickly while still conserving energy. Raubenhelmer [19] monitored the dives of Gannets with a video camera and concluded that Gannets choose their dive performance from flight. Considering the vertical axis as a reference, they enter the water at a larger angle for a shallow dive, and enter at a smaller angle for a deeper dive. ...
Conference Paper
In this effort, a nonlinear reduced-order model is proposed, aimed at answering the question of why the gannet bird does not injure itself during diving. In doing so, the critical velocities at which buckling will occur for various boundary conditions in vertical dives are obtained and the resulting forces at the point of impact are investigated. The gannet-inspired system is modeled as an Euler-Bernoulli beam to represent the body of the gannet, while the head of the gannet is modeled as a cone with varying half-angles. The initial experimental investigations of gannet-like diving systems are first presented to demonstrate how varying parameters will affect the overall behavior of the system. Next, the resulting forces during impact are investigated and a study is conducted to compare various approximations of the coefficient of drag for the cone-shaped head. The boundary conditions and nonlinear equations of motion for the structural system are derived using the Hamilton’s principle. The characteristic equation, buckled configurations, critical velocities are determined for each set of boundary conditions. The results show that the system with the smallest half-beak angle and beam length will delay the critical velocity and is most representative of a gannet during diving. The obtained results demonstrate a qualitative agreement with the conducted experiments. For clamped-clamped boundary conditions, the critical velocity was found to be the greatest because of the increased stability at both ends of the beam. It is also noted that a nonlinear approximation for the coefficient of drag offers the best fit with the provided experimental values when compared to a hyperbolic tangent approximation, which predicts the coefficient of drag to be less than that obtained in experiments, and thus predicts that the systems will buckle at higher velocities.
... In addition to providing persistent and predictable foraging habitats, fronts are also thought to increase the catchability and accessibility of prey [20,22]. In gannets, foraging strategies are especially energetically expensive [48,52,81,82], and to maximize efficiency individuals adjust their underwater movements in response to the behaviours and depth distributions of their prey [49,51,83,84]. V-shaped dives dominated gannet foraging strategies across the Celtic Sea, which possibly suggests this method of prey capture is better suited than a U-shaped dive strategy to the types of prey naturally encountered in the region (e.g. ...
Article
Full-text available
Oceanic fronts are key habitats for a diverse range of marine predators, yet how they influence fine-scale foraging behaviour is poorly understood. Here, we investigated the dive behaviour of northern gannets Morus bassanus in relation to shelf-sea fronts. We GPS (global positioning system) tracked 53 breeding birds and examined the relationship between 1901 foraging dives (from time-depth recorders) and thermal fronts (identified via Earth Observation composite front mapping) in the Celtic Sea, Northeast Atlantic. We (i) used a habitat-use availability analysis to determine whether gannets preferentially dived at fronts, and (ii) compared dive characteristics in relation to fronts to investigate the functional significance of these oceanographic features. We found that relationships between gannet dive probabilities and fronts varied by frontal metric and sex. While both sexes were more likely to dive in the presence of seasonally persistent fronts, links to more ephemeral features were less clear. Here, males were positively correlated with distance to front and crossfront gradient strength, with the reverse for females. Both sexes performed two dive strategies: shallow V-shaped plunge dives with little or no active swim phase (92% of dives) and deeper U-shaped dives with an active pursuit phase of at least 3 s (8% of dives). When foraging around fronts, gannets were half as likely to engage in U-shaped dives compared with V-shaped dives, independent of sex. Moreover, V-shaped dive durations were significantly shortened around fronts. These behavioural responses support the assertion that fronts are important foraging habitats for marine predators, and suggest a possible mechanistic link between the two in terms of dive behaviour. This research also emphasizes the importance of cross-disciplinary research when attempting to understand marine ecosystems.
... Both the dive type and depth attained may be influenced by intrinsic factors such as an individual's mass as well as extrinsic factors, including the type of prey and its depth distribution, which in turn may be influenced by the presence of other predators and the structure of the water column (Elliott et al. 2008, Machovsky Capuska et al. 2011). In addition, recent work demonstrates that dive type is determined before birds enter the water (Machovsky Capuska et al. 2013), suggesting that gannets use visual cues predive in order to optimize their foraging performance. Therefore, sex-specific differences in diving behaviour should arise as a consequence of habitat segregation as individuals adjust their foraging technique for different prey or habitats (Garthe et al. 2000). ...
Article
Full-text available
Sexual segregation, common in many species, is usually attributed to intra-specific competition or habitat choice. However, few studies have simultaneously quantified sex-specific foraging behaviour and habitat use. We combined movement, diving, stable isotope and oceanographic data to test whether sexual segregation in northern gannets Morus bassanus results from sex-specific habitat use. Breeding birds foraging in a seasonally stratified shelf sea were tracked over 3 consecutive breeding seasons (2010-2012). Females made longer trips, foraged farther offshore and had lower δ13C values than males. Male and female foraging areas overlapped only slightly. Males foraged more in mixed coastal waters, where net primary production (NPP) was relatively high (>3 mg C m-2 d-1) and sea-surface temperature (SST) was relatively low (15°C) more than females, possibly as a consequence of foraging in productive mixed waters over offshore banks. Females foraged most frequently in stratified offshore waters, of intermediate SST (12-15°C), but exhibited no consistent response to NPP. Sex-specific differences in diving behaviour corresponded with differences in habitat use: males made more long and deep U-shaped dives. Such dives were characteristic of inshore foraging, whereas shorter and shallower V-shaped dives occurred more often in offshore waters. Heavier birds attained greater depths during V-shaped dives, but even when controlling for body mass, females made deeper V-shaped dives than males. Together, these results indicate that sexual segregation in gannets is driven largely by habitat segregation between mixed and stratified waters, which in turn results in sex-specific foraging behaviour and dive depths.
... Both the dive type and depth attained may be influenced by intrinsic factors such as an individual's mass as well as extrinsic factors, including the type of prey and its depth distribution, which in turn may be influenced by the presence of other predators and the structure of the water column (Elliott et al. 2008, Machovsky Capuska et al. 2011). In addition, recent work demonstrates that dive type is determined before birds enter the water (Machovsky Capuska et al. 2013), suggesting that gannets use visual cues predive in order to optimize their foraging performance. Therefore, sex-specific differences in diving behaviour should arise as a consequence of habitat segregation as individuals adjust their foraging technique for different prey or habitats (Garthe et al. 2000). ...
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Full-text available
Sexual segregation, common in many species, is usually attributed to intra-specific competition or habitat choice. However, few studies have simultaneously quantified sex-specific foraging behaviour and habitat use. We combined movement, diving, stable isotope and oceanographic data to test whether sexual segregation in northern gannets Morus bassanus results from sex-specific habitat use. Breeding birds foraging in a seasonally stratified shelf sea were tracked over 3 consecutive breeding seasons (2010-2012). Females made longer trips, foraged farther offshore and had lower delta C-13 values than males. Male and female foraging areas overlapped only slightly. Males foraged more in mixed coastal waters, where net primary production (NPP) was relatively high (>3 mg C m(-2) d(-1)) and sea-surface temperature (SST) was relatively low (<10 degrees C). Males also tended to use areas with higher SSTs (>15 degrees C) more than females, possibly as a consequence of foraging in productive mixed waters over offshore banks. Females foraged most frequently in stratified offshore waters, of intermediate SST (12-15 degrees C), but exhibited no consistent response to NPP. Sex-specific differences in diving behaviour corresponded with differences in habitat use: males made more long and deep U-shaped dives. Such dives were characteristic of inshore foraging, whereas shorter and shallower V-shaped dives occurred more often in offshore waters. Heavier birds attained greater depths during V-shaped dives, but even when controlling for body mass, females made deeper V-shaped dives than males. Together, these results indicate that sexual segregation in gannets is driven largely by habitat segregation between mixed and stratified waters, which in turn results in sex-specific foraging behaviour and dive depths.
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From crocodiles and penguins to seals and whales, this comprehensive and authoritative synthesis explores the function and evolution of sensory systems in animals whose ancestors lived on land. Together, the contributors explore the dramatic transformation of smell, taste, sight, hearing, balance, mechanoreception, magnetoreception, and electroreception that occurred as lineages of amphibians, reptiles, birds, and mammals returned to aquatic environments. Each chapter integrates data from fields including sensory physiology, anatomy, paleontology, and neurobiology. A one-stop source for information on the sense organs of secondarily aquatic tetrapods, Sensory Evolution on the Threshold sheds new light on both the evolution of aquatic vertebrates and the sensory biology of their astonishing transition.
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