Deer vs salamanders
I have both heard from numerous respectable naturalist friends and read on different reputable websites (e.g. NH Fish & Game’s website) that if you took all of the red-backed salamanders in New England and put them on one side of a scale and then did the same with white-tailed deer (or any other vertebrate), the scales would tip in favor of the red-backed salamanders. Glenn and I did some real rough guesstimations and it seemed like this would be an absolutely mind boggling feat on part of the salamanders if there was more biomass of these tiny critters than those giant cervids. So is it?
In New England Wildlife, a compendium of the life history of New England’s vertebrates species, there’s a passage that reads: “The redback [sic] salamander is the most abundant terrestrial vertebrate in New England and accounts for the greatest amount of vertebrate biomass in the Hubbard Brook Experimental Forest in New Hampshire (Burton and Likens 1975).” I believe it’s this passage that has given rise to the extrapolation that salamanders must also account for the greatest amount of vertebrate biomass in all of New England.
Estimating red-backed salamander population size
The cited study is a fascinating read. The researchers used a few different methods to estimate population sizes, with pretty different results. Using mark-recapture (and the assumption that only 2-32% of a population of salamanders are found in the top 2.5cm of soil), they determined that the population of red-backed salamanders at Hubbard Brook was somewhere between 1,650 and 27,200 per hectare, which scales up to 427,350 and 7,044,800 individuals per square mile!! Burlington is 10.5 square miles, so prior to European colonization when the area was forested, at the high end, the population would be ~72 million salamanders (roughly the population of the UK or Thailand).
The number was less impressive when they used transects to count red-backs. These estimates were closer to 2,000 individuals per hectare. Averaging their various counts/methods, they list the population of a 36 hectare plot in Hubbard Brook as 90,000 individuals, about 648,000 red-backed salamanders per square mile).
Estimating deer population size
Like salamander populations, deer densities vary for deer depending on habitat and climate. While red-backed salamander populations increase in wooded areas, deer have higher densities in rural/agricultural habitats. Estimates aren’t always reliable as some counts of deer density are measured in areas of cover rather than total land area (so this excludes open fields in calculating land area even though deer might spend a significant amount of time feeding in these fields). A Wisconsin report that used total land area found densities up to 80 deer per square mile (source)!! If you’re handy with GIS/Google Earth, you can find lots of great info here: data on deer density.
Doing the math
Alright, so how do salamanders stack up against deer? Bear with me while I do some quick math:
- Deer weight depends on sex (females = 90-200 pounds, males = 150-300 pounds), age, and season. The average is somewhere in the neighborhood of 150 pounds.
- 1 average deer = 150 * 454 = 68,100 red-backed salamanders
- A red-backed salamander weighs some between 0.5 – 1.0 grams, about as much as a paper clip.
- There are ~454 grams in 1 pound
- 648,000 salamanders = 1,430 pounds of salamander per square mile
- This is the equivalent of 9.5 deer per square mile
So who weighs more, deer or salamanders?
We now need to figure out if there greater or fewer than 9.5 deer per square mile here in Vermont. Vermont’s total deer population is ~150,000 (source). Our state is about 9,614 sq miles, so the average deer density is about 15.6 deer per sq mi. The deer aren’t evenly spread out across the landscape: there are about 8 deer per square mile in the cold, boreal forests of the NEK and a staggering high of 28 deer per square mile in the St Albans area (great map). The average red-backed salamander population in a wooded area in NH was equivalent to about 9.5 deer – the density of red-backed salamanders across Vermont is much much lower as their numbers drop off significantly in suburban, agricultural, and high elevation areas.
Final Verdict: It’s a myth
It’s not even close. With 15.6 white-tailed deer per sq mi, the biomass of deer is nearly double that of red-backed salamanders across the region.