I’ve been classifying mammal observations and I’m wondering why there are so many dead mice, shrews and voles with no apparent injuries. Is it because of their short lifespan? Or diseases they carry?
I’ve personally found a few rodents on the roadside or boulevard without obvious injuries or signs of illness.
HI and welcome to the forums!
I think this is a observation bias. Generally, populations of rodents are rather large. However, due to their way of life it is difficult to observe them alive, let alone get an observation for iNat out of it if you do not specifically plan for it.
However, you do find them occasionally dead, and in most cases I would think cats are involved in that. They are known to play with their prey without necessarily eating them (as pet cats are probably well fed at home).. in those cases they rarely show external wounds but bleed to death internally.
I do have several observations of mice and rats and shrews, however, basically all of them were dead except one rat that fell in our enclosed backyard and did not find a way out.a
I agree that there is definitely observation bias. I would also say that in some areas where rodent poisons are used, it is not rare to find dead rodents without obvious injuries. Unfortunately the predators that eat rodents tend to find these also, and often are sickened or killed by the poisons.
Observation bias because not a lot of people go looking for living rodents. The living ones are usually pets, squirrels, or capybaras. Murids and similar rodents do a really good job of staying out of our line of sight unless they become roadkill, prey for domesticated animals, or get trapped in a combine.
Sometimes they also just die of shock if they get scared and don’t show any severe external injuries. I saw a dead shrew or vole in my backyard once and it had very few injuries that would be associated with cat bites or puncture wounds, but I would assume it dropped dead because there were mowers and leafblowers (very loud!!!) nearby. My household is very reluctant to use poison, and when we do it’s just the blue liquid ant killer with entrances too small for rodents to access the poison. Deaths like these are usually fear related I think.
I have also read, although I forget where, that because they are usually seperated from their mother early that they don’t actually know what to do with the prey. They have the instinct to hunt, but once captured, they don’t actually know what to do with the prey because their mother didn’t get the chance to teach them.
I would also agree with the observation bias. I would bet a large percentage of users (including myself) are only taking opportunistic pictures with their phones. That would be difficult to do for something with a high drive to hide from potential predators. I’ve only had one decent look at a mouse in my yard, and even if I had my phone at the time, it was gone by the time I would’ve got it out.
I think I remember reading that predators will catch shrews - and then figure out they are not tasty. As for other small mammals, I haven’t a clue.
I have often wondered about this since I find a LOT of dead shrews out on trails (where there is no evidence of house cats). I’ve posted six or seven of them.
I’ve only managed to photograph one live shrew, however, so observational bias is definitely a factor.
I can vouch for the fact that rodent populations are often larger than we humans realise. About a year ago my wife said she thought she had seen a rat in the backyard. I set up a trap camera and left it out overnight. The number of black rats, (Rattus rattus), captured was disconcertingly large. They appeared to be feeding on seeds falling from ornamental palms. We had never had any damage from rats in the house and its surrounds or to the vegetable garden which I would have thought might be a tempting target.
Agreed with other comments. Feral cat is major killer of rodents, shrews and moles etc. they only eat heads, organs or just kill them without eating because they’re usually very well fed by human or small native creatures.
Also many small rodents are nocturnal (AFAIK) and hide very well. it’s like we can’t easily find alive snake but roadkilled snakes.
at least for me, i take photos of things i see, i dont usually go looking for things. so of course its way more common to come across dead rodents to get observations of.
unless you can catch them faster…
or get a picture of the mole your dog dug up while also keeping the dog from grabbing it
Is that dark rectangle below your hand a mousepad?
I have seen a lot of voles running around in tall grass but never any living shrews, just dead ones. I know they starve very easily though so maybe that has something to do with it.
Oh yeah! I found a dead shrew a few weeks ago on the grass and it didn’t seem to have any injuries but maggots were crawling inside of its mouth. A year ago I found a dead rat on the sidewalk. Didn’t seem to have any major injuries on it I guess but it had very wet fur and looked like it was rotting and the only injury it seems to have is that some of its fur is ripped off. Maybe some insects like ants or maggots ate its fur off. But I once found a dead rat with obvious injuries and it was one that was for some reason in my breezeway and my cat clearly killed it because its leg was bitten off and it had multiple bite marks on it. I wonder why so many dead rodents I find don’t even seem to have any injuries at all like they died naturally or died from some disease or something.
