What is the primary cause of death for small animals in urban and suburban areas?

Question

Small birds (sparrows, robins, jays, finches) and mammals (squirrels, rats, opossums, raccoons) are a common sight in many urban and suburban communities with green space. However, I observe carcasses of these animals relatively infrequently.

I imagine that the following are some of the most common causes of death:

• Predation (the species I mention are small, and somewhere in the middle of the food chain)
• Age-associated decline in foraging ability, leading to starvation
• Disease
• Fatal contact with infrastructure (collisions with buildings or wind turbines, contact with electricity lines)

I can think of two reasons why we don't see carcasses very often:

• predation is the most common cause of death
• individuals that succumb to disease/starvation end up in their nests/dens

Is this plausible? Has this been studied systematically, e.g. in populations of birds with tracking bands?

Answer 1

It's quite hard to generalize, but this paper seems to suggest anthropogenic mortality increases with body size in mammals. Hence, small mammal mortality would be caused more by predation/competition/diseases than roadkill, imho.

To answer your question why we don't see so many carcasses, I would say that scavenging is very common and i don't see why a 'perfectly fine' protein source should be wasted.

Answer 2

The overwhelming cause of death of small animals ( and deer) that I see is that fearsome predator , the Toyota, Ford, Chevy, etc; AKA roadkill. I am in suburban E.TX. Other than that ,Coopers Hawks are common here and take many small birds. Also barred Owls are common and they are eating something. I think it is politically incorrect to estimate how many birds and bats are killed by wind turbines so those will be difficult numbers to get and they are not located in suburban areas. There are individual studies such as the local college studied the life cycle of Carolina Wrens ; but I doubt you will find anything covering the range you are asking about.