Vertebrate Pest Management (Dave Pehling) Slide 1 In this session, we are going to talk about vertebrate pest management. Vertebrates, as you know, are those animals that have backbones that include animals such as mammals, birds, reptiles, fish, and amphibians. We are going to be concentrating primarily on the fury and the feathered critters. Slide 2 One of the important concepts to be aware of in dealing with vertebrates is that of carrying capacity. This is the actual physical number of animals that can exist in any given area for any length of time. You can think of the carrying capacity of any given area as being like a gallon bucket and the animal in question being water. If you try and fill a gallon bucket with more than one gallon of water, the excess runs off as lost. Likewise, if your little garden can comfortably support say fifty voles, well voles breed year around and will keep doing it. The excess young, those over the carrying capacity, will either die, or the adults will kill them, or they will migrate away and try to find living places elsewhere. Slide 3 The carrying capacity of any given area is determined, at least in part, by three limiting factors: food, water and shelter. There are some other variables involved but these are the main ones. If we can eliminate or reduce any one or any combination of these for any given animal, we can effectively reduce the carrying capacity of an area and sometimes keep a population below our particular aesthetic or economic threshold. Slide 4 So, let s start talking about the critters. We are going to spend quite a bit a time with the commensal rodents. Commensal means animals that live with us. These are the rats and mice, the non-native rats and mice in particular. These are animals in the order Rodentia. Slide 5 We are going to be talking primarily about roof rat, Rattus rattus; the Norway rat, Rattus norvegicus; and we will also touch on the little house mouse, Mus musculus, and a native species. Page 1 of 6
Slide 6 There are all sorts of damage that is caused by the commensal rats and mice. They are of course notorious for spreading a wide variety of diseases. Norway rats can carry something like twenty different diseases that can be passed on to people, pets, and livestock. That does not mean that if you have a rat in your yard that you will die of the plague. But, these animals can carry disease so we want to keep them out of our environment as much as possible. They can and do eat crops. They will destroy flowers while they are feeding on them. They will eat animal feed, human feed, they will eat all sorts of things. They will destroy property by their chewing habits. They will kill wildlife and small livestock. They are socially unacceptable. You don t want your neighbor to know if you have a lot of rats around your house. Slide 7 These are just a few of the diseases that can be spread by rodents. We are not really going to go into these in depth, but we will talk a little bit about Hantavirus. Slide 8 This is some of the damage to crops and ornamentals that can be caused by rodents. This is primarily rat damage. In fact, that picture in the upper right was sent to me by a client. That is a roof rat feeding on the nectaries of a camellia. And this was taken during broad daylight, which is very unusual. Slide 9 The physical damage from chewing can be very extensive. They can chew right through two by fours, poorly cured concrete, thin sheet metal, they will chew on electrical wires, and have burned down houses by doing that. They have flooded houses by chewing on plastic water pipes and drain pipes. Norway rats, in particular, do a lot of tunneling around a house. Slide 10 This is the rodents tool kit. These huge incisors grow at a length of five inches per year for the Norway rat. They are very hard, they are very sharp, and can chew through a huge variety of things. Slide 11 We will start with the Norway rat, Rattus norvegicus. This traditionally has been our primary rat in western Washington. They get up to eighteen inches long, average about a pound, they can be larger. A lot of the rats you will catch in traps are smaller; those are the younger rats. Page 2 of 6
Slide 12 This animal is a robust burrowing rodent. It spends a lot of time tunneling, digs a lot of holes, which are usually about two and a half to three inches in diameter. You can tell a burrowing animal usually because the ears and eyes are small. In this animal, the muzzle is also blunt. Notice the thick musculature on the hindquarters, very heavily built. The tail is shorter, or at least no longer than the head and body combined. And, that is an important way to tell a Norway rat apart from the roof rat, which we ll talk about in a moment. Slide 13 This is a medium-sized Norway rat caught near Granite Falls, Washington. This is the standard color we ll find on the west side. East of the mountains they may be lighter in color. The color can range through grays, through browns, to almost black. Slide 14 This animal can breed year around. It is incredibly prolific. The breeding age is usually about three months, but they have been known to start as early as one month in really good circumstances. They can have up to twelve liters per year with up to twenty two per litter, although that is extraordinary. Slide 15 The other common rodent we have, in fact it is becoming more and more common along the coast, is the roof rat, Rattus rattus. I want to talk a little bit about common names. Common names can really get you into trouble. This particular rodent is known as the roof rat but also the tree rat, citrus rat, plague rat, black rat, Alexandrian rat; many, many common names. If you call it Rattus rattus, any place in the world entomologists will know exactly the animal you are talking about. Likewise the Norway rat, that rat is not from Norway. I don t know what it is called by that name. In Norway, possibly they call it the Swedish rat. Other common names include the brown rat, the barn rat, dwarf rat many common names. Getting back to the roof rat. This animal can be as long as the Norway rat, but it is lighter in build. This is a graceful, climbing animal. This is not as prolific as the Norway rat, but still it can churn out a lot of young per year and those young are capable of breeding in the same year. Slide 16 As you can see from the diagram, this is an animal that is much lighter in build. It has larger ears and larger eyes, which indicates it probably doesn t do as much tunneling. The tail is distinctly longer than the head and body combined. It uses the tail in balance for climbing. That is a really good way to tell Rattus rattus from Rattus norvegicus. You Page 3 of 6
can t go by the color because I have caught black rats of this species and brown rats of this species in the same area. Slide 17 In fact, these are a couple of the common morphs of this interesting animal. It can be a charcoal black, an overall brown, or a brown with really pretty white under parts. The tail is unicolored on this, that is, it is the same shade on top as it is on bottom. For the Norway rat, on the underside of the tail, it fades to a lighter grayish color. Slide 18 The little house mouse is well known by most people. This is a very common commensal rodent in many urban and suburban houses and sometimes out in the rural areas too. This animal again can breed year around and is quite prolific. This is a little mammal, only about 6-8 inches long, usually around an ounce, there can be larger ones or smaller ones. Slide 19 You also need to know about this little native. This is the deer mouse, Peromyscus maniculatus, is the Latin name, a very musical Latin name. This animal is a little bit larger than the common house mouse and is very, very common throughout North America. There are several species and varieties. This animal occurs all over and they are usually very similar to this color. The color variation isn t as wide as the other rodents we have been talking about. In particular, this animal has a distinctly bi-colored tail. That is the easiest way to tell it apart from other rodents. It is not as prolific as the non-native commensal rodents. Still you can wind up with a lot of deer mice. These animals will invade houses in rural and even sometimes suburban areas. Slide 20 It is important that you know how to identify deer mice because this is the vector of Hantavirus in much of North America. And it is the only vector of that disease in Washington State. There are anywhere between 1 and 5 cases of this disease in the state every year. It has a fatality rate of approximately 30-33%, which is very high. It is actually a very common disease, so it is surprising that there are not a lot of people that catch it. An average of 14% of the deer mice surveyed in a random sample tested positive. If you want more information on this or pretty much any other disease, the Center for Disease Control has an excellent website. Slide 21 Mammals are hard to see. They tend to stay hidden most of the time. So by the time you start seeing them, quite often you have a very serious problem. So you need to play detective to catch a population before it gets out of hand. Page 4 of 6
Slide 22 If you are working in the attic or working in the basement, just pay attention. Look in dark areas. If you have blown-in insulation, look around where it meets the wall. Rodents like to run along vertical surfaces. So this is often where they leave their runways. In this shot, you can see where rats have matted down the insulation. Slide 23 Behind cabinets, behind stored boxes, places that accumulate a little bit of dust, if there are rodents present, you will often be able to find their trails. Here you can see some tracks of a rat. This was behind a cabinet. Slide 24 In places where there is no dust, you can even make your own tracking patch. For this, you can use wheat flour, or unscented talcum powder. Make a patch about 12 x 12, preferably along a vertical surface where you expect rodents to run. If anything goes through the powder, the tracks will show up very well. Slide 25 Rodents and in fact most mammals have oil in our fur. By constantly rubbing along vertical surfaces, or in this instance, as the rats are swinging below joists, eventually grease stains will be made on the surface. Usually this is after the infestation has been active for a while. Slide 26 For Norway rats in particular, one of the first signs are two and half to three inch holes showing up. Usually around a foundation, around a dog house, sometimes out in the landscape. The only other animal we have in western Washington that makes these holes is the native chipmunk. On the east side of the mountains, there are several species of ground squirrels that will do this. But, squirrels are diurnal, that is, they are active during the day, so you would be able to see them. Slide 27 This was a house in Everett. You can see the large amount of tunneling that took place under the porch. These people never saw rats, but they obviously had a pretty good infestation. Slide 28 Of course if you have rat holes showing up in two by fours, that is a pretty good indication there is a problem too. Page 5 of 6
Slide 29 Fresh droppings are also a reliable sign of infestation. Here we have a comparison of various kinds of droppings. The house mouse and deer mouse droppings are about the size, shape, and color of grains of burnt rice. Norway rat droppings can be up to three quarter inch long but typically they are more like three eights of an inch or so. It depends largely on the diet and age of the rodent. Slide 30 These are Norway rat droppings in a machine shed. Notice that they are blunt on the ends, mostly. Roof rat droppings tend to be more slender and more pointed on the ends. Page 6 of 6