Peregrine falcon

Kingdom: Animalia

Fig1. Perergine falcon in flight 

Phylum: Chordata

Class: Aves

Order: Falconiformes

Family: Falconidae

Genus: Falco

Species: F. peregrinus

This species is probably one of the more widely distributed of the raptors, famous for the speeds they reach during the pursuit of prey (White, Pruett-Jones & Emison 1980). But what is more interesting is that they also show different approaches when it comes to hunting their aerial prey.

Peregrine falcons as mentioned hunt avian prey, which occurs mostly in the open skies, taking prey out at high speeds of up to 125ms^-1, which in most cases is the result after initiating a dive (Tucker 1998). Though in order for them to reach such speeds during their dives and flight aerodynamic efficiency is required (Tucker, et. al 2000). This is achieved by maintaining a streamline form and folding their wings nearly flush to their body depending on how much the incline is and speed required (Tucker 1998).

Although, straight flight and its’ accuracy are affected by distance. As the distance of approach increases the falcon is more inclined to turn it’s head to use its’ monocular vision for precision, reducing aerodynamic efficiency (Tucker, et. al 2000).  

Peregrine falcons have been seen to show other flight patterns to hunt avian prey, with a primary focus on approaches from long distances in order to maintain aerodynamic efficiency. This flight pattern is referred to as the curved flight pattern, this allows the peregrine falcon to reach its’ destination and maintain an aerodynamic form over long distances (Tucker, et. al 2000). But aside from efficient flight, as mentioned by Tucker, et al. (2000 p.3762), other explanations for this behaviour include, hunting out of the sun and misleading prey.  In either case, the curved flight allows falcons to utilise the morning sun, making it difficult for prey to detect the approach and not being a straight approach the prey is less likely to startle (Tucker, et. al 2000).

Reference:

Tucker, V.A., Tucker, A.E., Akers, K. & Enderson, J.H. 2000, "Curved flight paths and sideways vision in peregrine falcons (Falco peregrinus)", Journal of Experimental Biology, vol. 203, no. 24, pp. 3755-3763.

Tucker, V. 1998, "Gliding flight: Speed and acceleration of ideal falcons during diving and pull out", Journal of Experimental Biology, vol. 201, no. 3, pp. 403-414.

White, C., Pruett-Jones, S. & Emison, W. 1980, "The status and distribution of the Peregrine Falcon in Victoria, Australia", Emu, vol. 80, no. 5, pp. 276-277.

Raptorial digestion?

You would think that raptors all digest their prey similarly and that their digestive systems wouldn’t show any difference.

Although, there are in fact differences between the digestive morphology and processes found in some raptors (Ford 2010, Smith & Richmond 1972, Duke, et. al 1975). The differences that are discussed in this blog focuses on digestive morphology, the formation of pellets and gastric pH of the stomach.

Unlike Psittaciformes (parrots) and most other birds, raptorial diet consists highly of protein in the form of small lizards, rodents, birds or fish where the piscivorous raptors diet consists of fish (Fowler, Freedman & Scannella 2009). However raptors when eating, tear fairly large morsels of flesh from its prey, consuming a large amount in a short time, where it is stored in the crop (lacking in Strigiformes) (Ford 2010).

The digestive process in raptors is also more chemical than mechanical, where they have a gland that secrete mucus and another secreting HCl and pepsin (Ford 2010). Allowing the breakdown of protein structures, even so raptors such as hawks and owls form pellets (Fig 1) (Ford 2010, Duke, et. al 1975). 
 Pellets are undigested compressed materials that are egested (regurgitated) from owls and hawks, though it is observed that the amount of undigested materials (mainly bones) in Falconiformes is lower than that of owls (Moon 1940, Duke, et. al 1975). Reasons for this include Falconiformes initially not ingesting as many bones in comparison to owls (swallowing prey whole) and that the gastric pH in the of owls are higher than that of the Falconiformes (Moon 1940, Duke, et. al 1975, Smith & Richmond 1972).

Fig1. Simple illistration depicting the process of pellet formation (sourced by: https://www.tes.com/lessons/PBj-79gS-EQIjQ/science-owl-pellets) 

Reference:

Duke, G.E., Jegers, A.A., Loff, G. & Evanson, O.A. 1975, "Gastric digestion in some raptors", Comparative Biochemistry and Physiology -- Part A: Physiology, vol. 50, no. 4, pp. 649-656.

Ford, S. 2010, "Raptor Gastroenterology", Journal of Exotic Pet Medicine, vol. 19, no. 2, pp. 140-143.

Fowler, D.W., Freedman, E.A. & Scannella, J.B. 2009, "Predatory functional morphology in raptors: Interdigital variation in talon size is related to prey restraint and immobilisation technique", Plos One, vol. 4, no. 11, pp. e7999.

Moon, E.L. 1940, "Notes on Hawk and Owl Pellet Formation and Identification", Transactions of the Kansas Academy of Science (1903-), vol. 43, pp. 458-465.

Smith, C.R. & Richmond, M.E. 1972, "Factors Influencing Pellet Egestion and Gastric pH in the Barn Owl", The Wilson Bulletin,vol. 84, no. 2, pp. 179-186.

Hearing how does it benefit raptors?

Raptors are as mentioned in previous blogs have keen eyesight in which they rely on in hunting. 

Although, some raptors such as owls you find morphological adaptations, such as having facial disks, as well as the positioning of the ears that allow them to locate prey (Singheiser, et al, 2010). But aside from the owls’ adaptations, sensitive acoustic hearing that allows them to locate prey isn’t exclusive to owls; this form of detection is also seen in diurnal raptors (Rice, 1982).

Fig 1. diagram indicating properties related to hearing in Barn owls and their position (source from

All About Owls)

Firstly, owls (Strigiformes) being nocturnal hunters their vision allows them to detect movement though it is limited; therefore to precisely locate and capture prey they are guided by acoustic location (Hausmann, et al 2009). For example, barn owls and their dish-shaped face allows the sound of fairly low frequencies to be heard, as well as the positioning of the right and left ears being asymmetric helps the owl orientated and locate their prey in the dark (Singheiser, et al 2010, Payne 1971, Hausmann, et al 2008).

Fig 2. Shown in this figure is a mouse with paper tied and trailed behind it, determining whether the owl locates prey by sound or sight in the dark (sourced from Konishi, M. 2012 )

Secondly, acoustic detection and location are also seen utilised by diurnal raptors such as the marsh hawk which detect small mammals concealed in long the grass, even though it would play a larger role in nocturnal raptors (Rice 1982). Though the marsh hawks have facial ruffs and display quartering behaviour (not typical of Accipitridae but seen in owls), they do not show the accuracy demonstrated by the owl (Payne 1971, Hausmann, et al 2008). As mentioned by Rice (1982), some tested marsh hawks would strike several times in the attempt to flush out or would miss their target.

This blog is not to say all owls and other raptors have similar acute hearing or accuracy with acoustic location.

Reference:

Hausmann, L., Plachta, D.T.T., Singheiser, M., Brill, S. & Wagner, H. 2008, "In-flight corrections in free-flying barn owls (Tyto alba) during sound localization tasks", Journal of Experimental Biology,vol. 211, no. 18, pp. 2976-2988.

Hausmann, L., von Campenhausen, M., Endler, F., Singheiser, M. & Wagner, H. 2009, "Improvements of sound localization abilities by the facial ruff of the barn owl (Tyto alba) as demonstrated by virtual ruff removal", Plos One, vol. 4, no. 11, pp. e7721. 

Payne, R.S. 1971, "Acoustic location of prey by barn owls (Tyto alba)", Journal of Experimental Biology, vol. 54, no. 3, pp. 535-569.

Rice, W.R. 1982, "Acoustical Location of Prey by the Marsh Hawk: Adaptation to Concealed Prey", The Auk, vol. 99, no. 3, pp. 403-411.

Singheiser, M., Plachta, D.T.T., Brill, S., Bremen, P., van der Willigen, Robert F & Wagner, H. 2010, "Target-approaching behavior of barn owls (Tyto alba): influence of sound frequency",Journal of Comparative Physiology A, vol. 196, no. 3, pp. 227-238.