Prey Remains of Magellanic Horned Owl (Bubo magellanicus)
at Perito Moreno, Southern Argentina

© Bruce G. Marcot, Ana Trejo
18 December 2006
updated 16 September 2007, with corrections on identifications and photo additions from A. Trejo

With thanks to Dr. Ana Trejo for identification and confirmation of the prey remains.
This page links to Marcot's Ecology Picture of the Week page on "Magellanic Horned Owl's Retreat: Nest & Prey Remains."  See that page for description of the nests and site location from which I gathered owl pellets for this analysis.  

Click each image for larger versions.

  

Typical evidence of feeding by Magellanic Horned Owl:
whole pellets (top) and partially digested mammal pelt (fur) (bottom).

After dissecting the numerous pellets collected at the nest site.
Femurs and other leg bones of rabbits and rodents (left); 
lower jaw bones and teeth of various rodents (right).
The lower row of the jaw bones are explained below.

 

Jaw remains of small rodents

Bunny or Coney Rat, Reithrodon auritus (family Muridae, subfamily Sigmodontinae).  Commonly distributed in the "southern cone" of South America from near the Andes crest eastward to the Atlantic.  

 

 

Reithrodon auritus cranium

 

 

 

Reithrodon auritus mandibles.

 

 

 

This is Argentine Long-tailed Rat (Oligoryzomys longicaudatus).

 

This is probably a species of Abrothrix, possibly Olive Grass Mouse (Abrothrix xanthorhinus).  Identification is uncertain, and this mouse species itself may be a complex of two Abrothrix species that inhabit forests and steppe grasslands.  

 

 

 

Southern Big-eared Mouse (Loxodontomys [= Auliscomys] micropus) mandibles.

All of the above prey species are sigmodontine rodents.  These are Neotropical mice and rats of order Rodentia, family Cricetidae, and subfamily Sigmodontinae.  They are very diverse and abundant in the Patagonian steppe of southern Argentina.
  

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Additional prey remains

 

Additional prey remains that I found include the following.  Click for larger images.

    European Hare

 
  

Leg and fur of European Hare (Lepus europaeus), an introduced species to the southern Patagonian steppe.

 

Leg bones of more European Hares.

 

Skull, top (dorsal) view, of European Hare.

 

Side view of skull of European Hare.

 

Underside (ventral) view of skull of European Hare.

 

Closeup of dentition of upper jaw of European Hare.

  

    Tuco-Tuco

 

The strong digging claws and foot of a tuco-tuco (Ctenomys haigi), which is a regionally endemic and threatened rodent species of family Ctenomyidae.  Tuco-tucos create extensive burrows.  Appearance of this species in the Magellan Horned Owl's pellets suggests that it was taken nocturnally when they may venture out of their burrows. 

 

Closeup of the tuco-tuco's digging claws.

 

Underside (ventrum) of skull of a tuco-tuco.  One of the upper incisors is missing, but note the size and strength of the remaining incisor, used to gnaw tough vegetation material.
 

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Trejo and Grigera identified 1,216 prey items in 522 pellets of this species in the same area.  They also found that Magellan Horned Owls take mostly (98.5%) rodents, and the rest being a variety of birds and insects.  They reported that the rodent species appearing most frequently in the pellets were *Eligmodontia morgani, *Abrothrix longipilis, Abrothrix xanthorhinus, Oligoryzomys longicaudatus, *Reithrodon auritus, and *Ctenomys haigi.  * denotes those prey species also found in greatest biomass within the pellets.

Source:

Trejo, A., and D. Grigera. 1998. Food habits in the great horned owl (Bubo virginianus) in a Patagonian steppe in Argentina. Journal of Raptor Research 32(4):306-311.

[Note that during their study, the owl species was included with Bubo virginianus (Great Horned Owl), but was later split out as Bubo magellanicus, Magellanic (or Magellan) Horned Owl.]

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This page links to Marcot's Ecology Picture of the Week page on 
"Magellanic Horned Owl's Retreat: Nest & Prey Remains."