I spoke in my last post of the introduction of two new small mammal species, this week I have seen firsthand the devastating effects on Barn Owls.
I have been ringing Barn Owl chicks at nests in Tipperary and east Limerick in the past few days. The chicks which we have been finding have been in very bad health and perilously under weight. The chicks are lethargic, under sized, their feathers are not as developed as they should be for their age and light. So light in fact that little hope can be held out for the survival of many of the individuals encountered. Some of the chicks we found weighed just over half of the appropriate weight expected for their age. The brood sizes were also depressed. Many of the nests contained the grizzly, mummified remains of nest mates who hadn’t made it. Chicks often seemed to be experiencing some form of intestinal problem; covered in faecal matter, the smell would turn your stomach.
What on earth is going on with these Barn Owls?
Firstly let me lay out a few facts. This area of Tipperary and east Limerick is the strong hold of one of our latest small mammal species arrivals, the Greater White-toothed Shrew. The Greater White-toothed Shrew occurs at very high densities within this region. Where this species occurs in any great numbers it constitutes the majority of the diet of the Barn Owl. Barn Owl chicks in this ‘Shrew Zone’ are being feed predominately on Greater White-toothed Shrews. These facts seem to implicate this Shrew species. Furthermore, the fact that this shrew species occurs at such high densities in the area would suggest that it isn’t quantity of food which is the problem for Barn Owls but quality.
Following this line of inquiry BirdWatch Ireland in collaboration with Queen’s University are examining the nutritional value of the Greater White-toothed Shrew. Well feed chicks that are starving to death seems counter intuitive, although a comparable situation has been well documented among men who found themselves isolated in the Canadian wilderness. Over a hundred years ago when people used to spend the winter trapping for fur in Canada’s vast wilderness they would subsist on a diet of hare meat. These men would then often starve to death, although they were seemingly well feed. The problem resides in the fact that although hare meat is nutritious in many respects, it lacks many essential vitamins and minerals. The men were expending more vitamins and minerals in digesting the hare meat than the meat was providing in return!
Could Barn Owls be experiencing a similar paradox, only time and further research will unlock this riddle.