Date: 1/7/18 10:07 am From: Alvaro Jaramillo <chucao...> Subject: RE: [MBBIRDS] Is there a rodent outbreak? -YES
Rodent population cycles have been studied intensively by ecologists, and they are still a bit of a mystery. Here the most cyclic rodent is the California Vole. Right now the voles are on a population high here in Half Moon Bay. They started being really noticeable from late spring last year. Barn Owls increased here in the late summer onwards, and are now quite common.
These cycles are understood in some respects, but there is still a lack of understanding on what really drives the cycle, and it may be a complex of various factors. Originally, it was thought to be food driven (lots of food, high reproduction, big population). But now it is often thought it may be due predator-prey interactions and disease. What is really odd is that the reproductive rate of the rodents changes over time, what controls the reproductive rate is not clear. It is also not clear why it happens, lowering of the reproductive rate is in direct contrast to a simple prediction from evolutionary theory, so it is clear that in these cases a lowering of the reproductive rate may actually confer an individual a higher chance of passing on their genes. This of course seems counterintuitive. Keep in mind that voles only live a few months, and generation times are short. So within a year, multiple generations have occurred. Lemmings, which are well known for their population cycles are relatives of voles. Our voles seem to have cycles that happen at about 4 year intervals. Barn Owls, White-tailed Kites, and Northern Harriers seem to be particularly responsive to increases in vole numbers and may be the ones that specialize on capitalizing on the boom part of the cycle.
But one does have to look at rodents species by species. I don’t think there is any evidence that in California multiple rodent species cycle in unison. If other species are high this year, it may be a coincidence with the vole cycle. Also it is not clear what the geographic scope of rodent cycles is. In areas such as Norway where this has been studied more, voles in one part of the country are not necessarily in the same cycle as those in other parts of the country. So while we may be having a high vole year here, it may not be the case elsewhere in California. In fact the lack of correspondence in the cycles is part of what the owls and diurnal raptors depend on. That way there are always some areas that are better for food than others. You could plot kite concentrations using eBird year to year and identify where the vole concentrations are in the winter!
From: <mbbirds...> [mailto:<mbbirds...>] On Behalf Of Cliff Bixler
Sent: Sunday, January 7, 2018 8:22 AM
To: Chris Hartzell <c.hartzell...>
Cc: DEBRA SHEARWATER <debiluv...>; <mbbirds...>
Subject: Re: [MBBIRDS] Is there a rodent outbreak? -YES
Just this last year they exploded. I think it was due to the good rainfall last year causing a fast growth in vegetation. A greater food supply encourages more litters. An extra litter causes exponential growth. I do know that we have had to be really at war with the rodents (wood rats and mice), traps, bait, cleaning up areas where they want to set up housekeeping, flooding burrows.
Up here in Bonny Doon there is no shortage of predators. I hear and see coyotes, bobcats and even Cougars. Owls are around but not so much in the summer when the most rodent breeding is happening. They are a little late to the party.
We got our lesson in spades back in 2011 when they colonized the underside of our house. One of them ate through a waterline to a dishwasher and flooded the downstairs of our house. We had to open up the subfloor, tear out the heater ducts and insulation, dry and dehumidify then tear out damaged flooring, drywall, the entire kitchen and fireplace. I was kind of a total rebuild of 2/3 of the downstairs. We were cooking outside and living upstairs for 5 months.
The simple answer is yes, there is. Going on a second year irruption of both Wood Rats and different Mice species. This is happening in multiple states from what I am hearing. Multiple automobile dealerships, mechanics, construction workers, and pest control people I have talked with in the last several months have seen a tremendous spike in rodent related infestation and damage. Subaru and Toyota have gone the last 10 years averaging about 10-20 cars with rodent damage. Last year they went to almost 100, this year over 200. Our outlying fire stations and engines have gone many years with minimal problems. My station has gone with a handful over the last 5 years. Starting the middle of last year, we caught 25 in 3 days. All our outlying stations are seeing a massive infestation as well. When I responded to the fire over in Fort Ord, I pulled up and watched literally over a hundred rats running from the fire. I had never seen this many so condensed before. It is not just here either. I am hearing almost the same reports out of multiple locations in Oregon, much of Montana, and friends in Salt Lake City are reporting similar. I have talked with some biologists and naturalists about it. As far as I have heard, there is no research actually being done and no one seems to be doing any formal study on it. Therefore the cause seems to be speculative as far as I've found out. So far the most supportive guess is a combination of reduction in predators and increase in drought type conditions. Drier climates have allowed for a spread in certain vegetation that is conducive to rodent spread while there also seems to be a drop in predators. I've noticed at my home and many of our stations that regular occurrences of bobcats and coyotes have gone down significantly. Additionally, I heard from many firefighters what seemed to be the lowest run-ins with snakes on fires in many many years. Personally, getting around and talking with people, I think it is a combination of inadvertent poisoning through rodent control, more hunting/trapping, and increased traffic resulting in more roadkill. I don't know why and haven't heard why there might be such a reduction in snakes.
Anyway, there is a major rodent problem. It cost Ame and I $1800 in repairs to two vehicles and six other personnel at my station have had their vehicles damaged. So keep the hoods up when it doesn't rain and put non-poison traps in the motor when you have to close the hood. The rodent problem is a major issue!
San Benito County has an abundance of Barn Owls, even in the worst of times. However, lately I have counted more BARN OWLS than usual. For instance, last night I saw 23 Barn Owls, 18 of which were along John Smith Road. This road is only 2.8 miles long. I did not use playback or a spotlight. The owls are easy to see, either sitting on fenceposts or utility wires.