Natural Heritage Program’s Winter Work: Revisiting Maryland’s Tiger Salamanders
Throughout a career in natural resources work, one of the questions I get most often is, “what do you do in the winter?” It is a common perception that there just isn’t much to do when it comes to field biology and conservation in the coldest season. It is true that the urgency caused by blooms and baby animals is less in the winter, but plenty of vital functions in the life histories of our native wildlife happen at this time of year.
For example, young macroinvertebrates survive and thrive in freshwater streams, enjoying less active predators and preparing for a spring and summer frenzy of hatches. The Department of Natural Resources’ staff at the Maryland Biological Stream Survey take advantage of this by conducting macroinvertebrate sampling in March and April, when stream temperatures are still cold and nobody has left the party yet; in other words, they find the most consistent species diversity at the end of winter and very early spring. Many of our native birds are also quite active in winter, like owls, who use the winter months to communicate with potential mates (check out this edition’s article by educator Edwin Guevara for more information, and we suggest the Merlin Bird ID app for helping to identify owl calls). Perhaps most surprisingly, some native amphibians are also very busy in the winter months- like the Endangered eastern tiger salamander (Abystoma tigrinum).
Tiger salamander research is nothing new for the Natural Heritage Program; keeping tabs on their populations is part of what we do in an effort to conserve species listed in Maryland as Endangered. In 2009, department biologist Scott Smith wrote an article for the Maryland Natural Resource magazine, offering excellent historical context to this ongoing project and a detailed description of this species’ winter activities.
“Though the tiger salamander is what is referred to as a cold-blooded creature, it is one of the earliest breeding animals in Maryland. Egg-laying has been recorded on the Eastern Shore as early as late November and as late as mid-March [recent work has shown breeding into early April]. Peak breeding usually takes place during the January thaw. Breeding may last only a few nights a year. It is more common for it to continue for some weeks, depending on rainfall, humidity, air temperatures and the availability of water deep enough for egg laying. Males leave their underground burrows after a few days of warm winter weather. In their quest to mate, they will often cross ice-encrusted ponds and slip into frigid waters where ice has melted. Females follow within a few days to two weeks. Reproduction may take place under the ice in some years […]. It is believed females leave the pond soon after they deposit their eggs. Males stay in the pond for weeks, attempting to mate with every female that presents herself, and depositing many spermatophores on the pond bottom in the course of one breeding season. Tiger salamander eggs normally hatch in about 30 days. The incubation period depends on water temperature, turbidity and the amount of shading. The larval period is highly variable — anywhere from 75 to 205 days depending on temperatures, water levels and food availability. Survival rates of larval tiger salamanders are extremely low due to predation by other salamander larvae, diving beetles, other amphibians, reptiles and wading birds. Ponds may also dry out before larvae fully develop. Tiger salamanders compensate for low survival of larvae by having amazing adult longevity. They have been recorded to live as long as 25 years, with the average lifespan believed to be about 18 years.”
In 2020, just a few days before pandemic chaos erupted in our human world, DNR scientists cheerfully reported increased population numbers in the winter salamander surveys. Fast forward to 2023 and the cooperative surveys continue, with the addition of some new land management practices. Forested wetland ponds have been intentionally opened up over the past 15+ years by carefully removing individual trees; since 2019, woody vegetation management has accelerated in select habitats. Tiger salamanders require a very specific combination of fish-free wetland conditions. On the Eastern Shore, the temporary pools they inhabit – called vernal pools – usually fill up during fall or winter rains and dry out by summer, creating an environment where predatory fish cannot survive.
Sadly, climate change, unusual storms, and other human impacts can mean these ponds don’t drain or can connect to larger water bodies, inviting fish to stay and feast. As the perfect salamander real estate becomes more and more rare, even the best vernal pools can be altered by natural processes like forest succession. This means trees can take over, shading out sunlight that can make the difference between life and death for young salamanders. Biologist Beth Schlimm now leads a team with the goal of preventing this succession in known tiger salamander habitat, giving these beloved creatures a fighting chance at survival. Redefined land management strategies have also increasingly prevented human impacts that can decimate a local breeding area, like commercial clear-cutting and aggressive logging (see figure below). Dedication to continuing these practices long-term could eventually mean the delisting of this species as Endangered!
What can Maryland residents do to help the eastern tiger salamander? The overarching lesson we’ve learned from decades of combined monitoring and land management is if we enhance existing habitat and protect it in areas they already occur, tiger salamanders will expand and thrive. Just like humans, they need housing options to choose from in order to successfully grow their populations and continue their life cycles. Locally, we can help by advocating for conservation and protection of large interconnected areas of land with vernal pools and forested areas around them, called buffers. Within these protected areas, we can fund and support the practices that science has shown to work. And remember, just like the biologists at the Natural Heritage Program and our beloved eastern tiger salamanders, conservation doesn’t stop in the cold winter months!
In this Issue
- In Praise of Dormancy
- Native Plant Profile: Evergreens
- Native Animal Profile: Stealthy (and Cute!) Owls
- A Cozy Winter Reading List for 2023