I'm pasting an excerpt from an email that I just got below. Extra-credit is available to anyone who can reseach this and explain it in their own words.
From the email:
Owl pellets...
Just got a notice from a vendor today that the owl pellets we use in 5th grade will be in short supply next year. Barn owls, which are the source of the pellets, are going through a natural cyclical decline that happens every 10 years or so.
I have not been able to find any information on Barn owls declining every 10 years or so, but I have found that they are declining. Land use changes, and the decrease in farms are some reasons for the decline. Also the predation of young barn owls by raccoons and that there has been a very high increase in rodent poisons which causes there to be less food for the owls. There are many other things that affect the lives of these owls but those are the most important. If nothing changes in the world then Barn owls will continue to decline. With this great decline of Barn owls they will have to be raised in captivity so that we can still have them on earth if not they will eventually die and never been seen again.
ReplyDeleteThe “Barn Owl Trust” (see barnowltrust.org) says that the first reliable census among Barn Owls was in 1999 (10 years ago). Apparently, before the 1990s, there was an extreme decline in the Barn Owl species. The Barn Owl Trust suggests that it was due to the wide spread increase of the use of rodent and mouse traps. Before many people began to use mouse traps, farmers put Owls that made a home in their barn to work by eliminating mice and rats. Although most people today farm or have barns with mice in them, it is an interesting perspective.
ReplyDeleteAlso, another thing I found from the Barn Owl Trust website was the survival percentage of different phases of a Barn Owl’s life (bottom of the page at http://barnowltrust.org.uk/infopage.html?Id=79). During their life, the Barn Owl life cycle is divided into various stages. The average percentage each category is as follows: The number of eggs laid: 5.6; hatching success rate: 4.5; nestling survival: 3.6; fledging success: 2.4; the average first-year survival is 25% and the annual adult survival is 63%. From this data, I could just see that this year happens to be a year where “the planets align” and it is just an off year for the species of the barn owl.
From http://www.owlpages.com/news.php?article=389, I found that barn owls have a large mortality rate and live only about two years. Perhaps Wil is right about this being an "off year" for the owls and, considering their lifespan, maybe they naturally die out around the same time. The website also mentioned that these owls need a large amount of grasslands in order to find enough rodents to feed their families. Such grasslands, along with barns and buildings for the owls to nest in, are beginning to be industrialized. An explanation on http://www.conwy.gov.uk/upload/public/attachments/47/BarnOwlv2.pdf said that changes in agricultural products could be partly to blame. Barn owl prey is abundant in hay barns: however, with farms switching to silage, there aren't proper places for the rodents to hide. I live on a dairy farm and we produce silage as well as hay. The claim that farms are now producing only silage is confusing to me because producing silage is more expensive than producing hay. Maybe if more people realized the price difference and the effects this has on the barn owl population, they would continue to have hay in their barns. These points give reason to the decline of barn owls, but they do not explore the fact that a decline happens every ten years.
ReplyDeleteAlso on http://www.conwy.gov.uk/upload/public/attachments/47/BarnOwlv2.pdf, they stated that long, wet winters cause loss of barn owls, so maybe the ten year drop has more to do with weather patterns that anything else. This opens up the question if the winter ten years ago was as consistently wet and cold as it has been this year.