Fish Eating Northern Harriers

 As I’ve mentioned before in this blog, the winter of 2008 was a particularly brutal one in northern Utah.  During January and February there was much more snow than usual and it was bitterly cold.  During most winters our Northern Harriers rely primarily on voles as a food supply but in 2008 with the voles under the deep crusty snow our harriers were desperate for food. 

Birds of North America Online provides extensive information on the dietary habits of harriers.  It lists small to medium-sized mammals (primarily rodents), birds, reptiles and frogs as harrier food sources, stating further that the diet of harriers during winter in their northern range (which includes northern Utah) consists of voles “almost exclusively”.  I can find no mention of harriers eating fish, ever!

Each year in early February some of our wetlands managers treat some of our ponds with rotenone (a chemical that prevents oxygen from being absorbed across fish gill membranes) in an effort to control the invasive and damaging carp that do so much damage to the emergent vegetation which is so vital for waterfowl.  So, in 2008 for a few weeks, our desperate and starving harriers began to eat fish!  In the three winters since then I have never seen harriers eating fish even though the dead carp are always plentiful after the rotenone kill. 

 

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Many of the carp are brought to the shores or ice surface by Bald Eagles which makes them available to the harriers who generally cannot retrieve them from the water. 

 

 

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An immature male harrier landing on a small carp. 

 

 

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As you can see in the background, at times the eagles provided a bounty of fish for the harriers to eat.

 

 

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Harriers would often compete for and even fight over the fish.  These are typical threat/possession postures when more than one bird was on the carp. 

 

 

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This immature male was sated and apparently not hungry but he still couldn’t resist claiming possession of the fish by continually resting his foot on the carp as he watched warily for other birds to come in and challenge him for the prize.

 

 

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But males are roughly one third smaller than adult females (sexual dimorphism) and whenever a male would see an adult female coming in to challenge him for the food he would beat a hasty retreat, as this one is preparing to do.

 

 

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Here’s another posture that apparently displays “possession” to other birds in the area.  At times they would even spread their wings over the  fish as they were eating.  

 

 

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However, “possession displays” often didn’t work and fights were commonplace.

 

 

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Less dominant birds were often left to feed over scraps. 

 

 

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And at times those scraps were minimal indeed!

 

 

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A few carp were quite large but even the big ones were quickly picked clean by the ravenous harriers.

 

 

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At times more than one bird would feed on a fish simultaneously but it wasn’t a comfortable arrangement and their stress from doing so was obvious.  But when another bird would come in to challenge them…

 

 

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it could be pretty dramatic! 

 

 

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Landing on the carp’s head.  This harrier had a particular fondness for perching on the head of the carp even when it wasn’t feeding.

 

 

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As an indication of just how difficult this particular winter was for a variety of birds this Song Sparrow spent quite a while feeding on what’s left of this fish – something I have never seen before.  If you look carefully you can see a morsel of fish flesh in the tip of the bill.  The winter of 2008 was very good for bird photography but extremely difficult for many of our birds.  For their sake I hope such conditions don’t happen again soon.

Ron

PS – a word of explanation about my camera settings (techs) for these images.  Many of them were poorly chosen, even illogical.  My excuse is that at the time I was still a digital photography beginner and had very little experience with my new 500 mm lens.  My chosen settings for most of these shots would be quite different now.  All images in this post were taken with a Canon XTi, Canon EF500mm f4L IS USM lens, mostly with attached 1.4 tc, from a tripod (some from within a blind).