Muddy Waters and Finding the One

Imagine you’re on a date—not just any date, the dreaded first date. It’s going reasonably well, but then the lights in the restaurant go out. You think maybe this isn’t a bad thing, candle-lit dinners are romantic right? The waiters are rushing around trying to get the candles lit, so in the mean time you have three choices. 1) Try harder to make yourself heard over the commotion. 2) Call the date a dud and go home. 3) Make a fool of yourself by spilling your wine all over the table, yourself, and your date, then go home.

Now let’s reimagine this scenario. Instead of a first date, there are two fish courting, and instead of the lights going out, a ton of mud has been dumped on their heads. This is the reality that many freshwater fish face. Turbidity, or the murkiness of the water, is increasing in many aquatic ecosystems due to high nutrient inputs increasing algal growth or greater inputs of soil. To visualize what fish courting might look like, check out the video of a male cichlid trying to woo a receptive female using a move appropriately termed a quiver. Fish in turbid waters can increase the time and energy they spend courting in hopes of attracting a mate, but this might not lead to increased reproduction for the male (the fish equivalent of making a fool of yourself?) (Candolin et al., 2007). In other words, it can be a waste of time. In colorful species like cichlids, turbid water leads to duller fish, fewer color varieties, and lower species diversity (Seehausen et al., 1997). Even when species do manage to choose a proper mate, turbidity can still hamper hatching success because the eggs become smothered and cannot obtain sufficient oxygen. Beyond reproduction, turbidity can also affect community structure, predator-prey dynamics, and cause infections by damaging gills (Gray et al., 2012a). In species that choose their mates based on visual cues, the inability to successfully choose a suitable mate could reduce population viability (Gray et al., 2012b).


Candolin U, Salesto T,  Evers M (2007) Changed environmental conditions weaken sexual selection in sticklebacks. J Evol Biol 20: 233-239

Gray SM, Chapman LJ,  Mandrak NE (2012a) Turbidity reduces hatching success in threatened spotted gar (lepisosteus oculatus). Environ Biol Fishes 94: 689-694

Gray SM, McDonnell LH, Cinquemani FG,  Chapman LJ (2012b) As clear as mud: Turbidity induces behavioral changes in the african cichlid pseudocrenilabrus multicolor. Curr Zool 58: 146-157

Seehausen O, van Alphen JJM,  Witte F (1997) Cichlid fish diversity threatened by eutrophication that curbs sexual selection. Science 277: 1808-1811

California: Banning Lead Ammunition to Save their Condors

The critically endangered California Condor (Gymnogyps californianus) is an avian scavenger and North America’s largest flying bird (West et al. 2017).  They have been experiencing population declines since the early 1950s and in 1980, the entire species consisted of only about 30 individuals.  Many doubted that these symbolic birds would do very well in captivity, but in 1987, all 27 of the remaining California Condors were captured and brought to a captive breeding facility. Teams of researchers from organizations such as the U.S. Fish and Wildlife Services, the Los Angeles Zoo, and the San Diego Wild Animal Park came together for these birds and by 1998, there were more than 150 California Condors (Meretsky et al. 2000). Today, there are now five breeding and release facilities in California and Mexico. There are now more than 400 California Condors, and half of these are flying free (National Park Service 2017).

So what was it that caused this species to drop to such small numbers in the first place? When scientists first started looking into this, they discovered that adults had higher mortality rates than immature condors (Meretsky et al. 2000). This was puzzling until they were able to study the tissues of dead condors and obtain blood samples from those that were captured for the captive breeding program. In the mid-1980s, lead poisoning was determined as the leading cause of death in wild California Condors (Wiemeyer et al. 1988).

Lead contamination is responsible for the deaths of millions of birds annually, and the main source of this is from hunting. California Condors are a scavenger species that feed on the carcasses of dead animals, and oftentimes they are feeding on carcasses that have been shot by hunters. Lead bullets, common ammunition used by hunters, shatter into tiny fragments upon impact. Because California Condors are known to scavenge communally, a single carcass containing these bullet fragments can poison several individuals (Kelly et al. 2014). Lead exposure was found to increase during hunting seasons. Sudden, severe symptoms of lead poisoning might include labored breathing, incoordination, and blindness. Chronic symptoms, which take longer to develop, might include changes in migratory movements or changes in bone mineralization, which increases the risk of bone fractures. The final stage of lead poisoning is death (Plaza and Lambertucci 2019).

Although eliminating lead from their environment is critical for the recovery of the California Condor, is it important to note that this is not the only contaminant that is threatening this species. Although California banned DDT in 1972, its influences are very present in this ecosystem today. DDE, a byproduct of DDT that does not get excreted from the body and actually becomes more concentrated over time, is consumed by the condors when they feed on marine mammal carcasses. Once ingested, DDE causes thinner eggshells, which increases the risk of the eggs breaking before the offspring have had a chance to develop (Kiff et al. 1979). Scientists have found that DDE disrupts the endocrine system of California Condors by changing the concentrations of reproductive hormones in their blood and the number of receptors that the hormones can send their signals to, which is what is ultimately causing the thinner eggshells. How lead is influencing the endocrine system in this species is not understood (Felton et al. 2015). Before we can fully address these contaminants that are reducing reproductive success through egg breakage, we need to focus our attention on reducing the amount of lead in the environment so we can increase the number of adults even attempting to nest.

The last two decades have seen the number of free-flying California Condors go from 0 to nearly 200 individuals. The real question is: are these birds still being affected by lead poisoning?

In 2008, California banned the use of lead ammunition for most hunting activities within the wild California Condor range. Annual blood samples found that the percent of these condors with more than 10 micrograms of lead per deciliter of blood was 67% prior to this ban (data from 1997-2008) and 62% after the ban (from 2008-2011) (Kelly et al. 2014). These results indicate that despite this ban, California Condors are still experiencing chronic exposure to lead poisoning. Because of this, California has decided to enact a state-wide ban on the use of lead ammunition for hunting, which is set to go into full effect on July 1, 2019. Perhaps this will be the key to the success of one of our country’s longest-running conservation programs. 




Felton RG, CC Steiner, BS Durrant, DH Keisler, MR Milnes, and CW Tubbs. 2015. Identification of California Condor estrogen receptors 1 and 2 and the activation by endocrine disrupting chemicals. Endocrinology 156(12): 4448-4457.

Kelly TR, J Grantham, D George, A Welch, J Brandt, LJ Brunett, KJ Sorenson, M Johnson, R Poppenga, D Moen, J Rasico, JW Rivers, C Battistone, and CK Johnson. 2014. Spatiotemporal patterns and risk factors for lead exposure in endangered California Condors during 15 years of reintroduction. Conservation Biology 28(6): 1721-1730.

Kiff LF, DB Peakall, and SR Wilbur. 1979. Recent changes in California Condor eggshells. Oxford University Press 81(2): 166-172.

Meretsky VT, NFR Snyder, SR Beissinger, DA Clendenen, and JW Wiley. 2000. Demography of the California Condor: Implications for Reestablishment. Conservation Biology 14(4): 957-967.

National Park Service. 2017. Condor Re-introduction & Recovery Program.

Plaza PI and SA Lambertucci. 2019. What do we know about lead contamination in wild vultures and condors? A review of decades of research. Science of the Total Environment 654 (1): 409-417.

West CJ, JD Wolfe, A Wiegardt, and T Williams-Claussen. 2017. Feasibility of California Condor recovery in northern California, USA: Contaminants in surrogate Turkey Vultures and Common Ravens. The Condor: Ornithology Applications 119(4): 720-731.

Wiemeyer SN, JM Scott, MP Anderson, PH Bloom, and CH Stafford. 1988. Environmental contaminants in California Condors. The Journal of Wildlife Management 52(2): 238-247.



All images were taken by former coworker, Louise Prévot, in Marble Canyon, AZ.

The Trouble with Turtles

If you’ve ever been to John F. Kennedy International Airport, you were probably worried about a lot of things: long security lines, delayed flights, grumpy New Yorkers. All are valid concerns. You probably didn’t spend much time worrying about turtles. Little did you know, turtles make their way onto JFK airport’s runways every year, sometimes delaying flights for hours (Reardon, 2011). The real trouble with terrapins, however, isn’t on JFK’s runways. It’s with their nests. Or really, the lack thereof. Researchers have been studying these terrapin populations for over a decade at Jamaica Bay Wildlife Refuge, a nature preserve just 5 km from JFK in New York. In that time, they’ve observed a 50% decrease in the number of diamondback terrapin nests laid each year (Rubenstein, 2014).

A female diamondback terrapin captured as part of a nesting behavior study at Jamaica Bay Wildlife Refuge.

What’s happening in Jamaica Bay to cause this decline? There are two parts to this problem. First, the whole terrapin population is declining (Reardon, 2011). Fewer females means fewer nests. The second problem is that females are laying fewer nests per year. Female terrapins usually next two to three times a year, but research suggests they may be nesting fewer times per year at Jamaica Bay Wildlife Refuge (Rubenstein, 2014). In both cases, it likely all comes down to one thing: food.

The health of Jamaica Bay, the body of water neighboring JFK airport and surrounding Jamaica Bay Wildlife Refuge, has long been declining. Four different New York City waste water treatments plants feed into Jamaica Bay, releasing tremendous quantities of nutrients such as nitrogen into the water (Benotti et al., 2007). Excess nutrients in the water have caused algae to proliferate, preventing other vegetation from getting the light and nutrients they need. Due to this nutrient pollution, as well as sea level rise, Jamaica Bay’s wetlands are declining at an alarming rate (Rubenstein, 2014). The amount of wetland vegetation in the bay declined by almost 40% from 1974 through 2002 (Hartig et al., 2002). This loss of wetland habitat has led to declines in terrapin’s main food sources: clams and mussels. So instead of eating protein-rich clams and mussels, terrapins are stuck eating algae (Rubenstein, 2014).

Jamaica Bay’s high nutrient levels cause algae to grow rapidly, covering beaches and depriving other vegetation of light and nutrients.

What’s so bad about eating algae? Algae doesn’t provide the same amount of proteins and other nutrients as clams and mussels. Proteins play a vital role in the production of energy and can have a big impact on an animal’s metabolic rate. Metabolic rate is the speed at which chemical reactions, such as the production of energy, occur in the body. All animals require a minimum amount of energy to keep their body functioning and survive. This minimum amount of energy needed, called the basal metabolic rate, is represented by the red line in the figure below. Metabolic rate depends on a number of factors, including temperature. For turtles and other ectotherms, which are animals whose body temperature depends on the external temperature, the minimum amount of energy an animal needs increases with temperature (Randall et al., 2008).

Adapted from:

An animal’s metabolic rate can also depend on the amount of food, and therefore energy, available. Any energy not used up by their basal metabolic functions can be used to fuel processes beyond just survival, such as growth and reproduction. The blue line in the figure above represents the maximum amount of energy an animal can use, called their maximum metabolic rate. The distance in between the basal and maximum metabolic rate represents the amount of energy that can be used for extra activities like growth and reproduction and is called the aerobic scope (Randall et al., 2008).

Since Jamaica Bay terrapins are stuck eating more algae and less protein-rich food, their ability to grow and reproduce may be compromised. All or most of the energy they get from their food may need to be used to maintain their basal metabolic rate just to survive. As a result, terrapins may not have the energy to reproduce as often, causing them to reproduce fewer times each year than in the past. If algae doesn’t provide enough energy for terrapins to meet their basal metabolic rate, individuals may not even be able to survive, which would explain the declines in population size that are also being observed.

If we truly want to understand why New York’s terrapins are reproducing less and less each year, further research about their metabolic needs, food availability, and population size is needed. But based on current evidence, large-scale efforts are needed to minimize nutrient pollution and to  preserve the remaining wetlands in Jamaica Bay if we hope to protect these terrapin populations.

By Becca Czaja 

Works Cited

Benotti MJ, Abbene M, Terracciano SA. 2007. Nitrogen Loading in Jamaica Bay, Long Island, New York: Predevelopment to 2005. USGS.

Hartig EK, Gornitz V, Kolker A, Mushacke F, Fallon D. 2002. Anthropogenic and Climate-Change Impacts on Salt Marshes of Jamaica Bay, New York City. Wetlands 22 (1): 71-89.

Randall D, Burggren W, French K (2008) Eckert Animal Physiology: Mechanisms and Adaptations. W.H. Freeman and Company, New York.

Reardon, Sara. “Why JFK’s Runway Has Turtles All the Way Down.” Science. 30 June 2011. Accessed 15 January 2019.

Rubenstein, D. “A turtle mystery in Jamaica Bay.” Politico. 30 October 2014. Accessed 15 January 2019.

Zoos & Researchers Team Up to Understand How Climate Change Affects Polar Bears

Below are screenshots of my twitter thread on the collaboration of zoo staff and scientists to understand metabolic rates and energetics in polar bears by training zoo-housed bears to inform us on their wild counterparts! It includes a lot of gifs, videos, and images that I think enhance the thread, so I recommend you check it out on my twitter, @Tori__Roeder. If you feel so inclined, you can follow me for animal and ecology content, though predominantly mammals and zoos.

Climate Change Effects on an Out-of-Control Population: The Case of the Snow Goose

The Migratory Bird Treaty Act was enacted in 1918 as an effort to conserve migratory birds within North America and aimed to maintain or increase populations of various migratory birds, including waterfowl. These efforts have been successful in most species, but now waterfowl managers face a problem of overpopulation in snow geese (Ducks Unlimited, n.d.). These birds have grown substantially in population size as population estimates indicate numbers exceeding 15 million geese (Ducks Unlimited, n.d.). They have also expanded their breeding and nesting ranges throughout the Canadian Arctic and Sub-Arctic. The over-grazing of these areas has caused snow geese to find new habitat, and have destroyed vegetation that is crucial for foraging in snow geese (Peterson et. al, 2013). Other problems that are related to climate change include the decreased fitness in snow geese, reduced body size and condition of goslings, and new predation risks.

Snow geese have breeding grounds in the northern parts of Canada, but overpopulation and climate change are causing ranges to expand. Source: Environment Canada


Snow geese are the main driving force in the habitat degradation in the Hudson Bay area. They impact the vegetation and soil in a negative manner, which creates large patches of barren ground and makes it difficult for these habitats to recover even after the geese have moved out of the habitat (Peterson et. al, 2013). Also, climate change has caused these geese to inhabit new areas and degrade them as well (Peterson et. al, 2013). This causes problems for fitness and survival of geese, as lower resources decrease reproductive success and gosling survival. Aubry et. al. (2013) studied the effects of climate change, phenology, and habitat degradation on the body condition in snow goose goslings. Their findings show that goslings that live within the center of populations where habitat degradation was the worst had lower body condition and lower survival rates. Also, warmer winters and summers due to climate change result in lower body condition

This image shows an area that has been fenced off to keep snow geese out. The landscape around it has been destroyed by over-foraging of snow geese. Source: Wek’eezii Renewable Resources Board

scores for goslings, likely due to the reduced forage nutrition in plants (Aubry et. al, 2013). These factors could lower snow goose populations as they are reducing their nutrition and destroying their habitat.

Another change that has been observed is the difference in timing of migrations in snow goose populations. Climate change has caused a change in weather patterns and has altered the timing of snow goose migrations. These migrations appear to be happening earlier in the year, and geese are returning to their breeding grounds and nesting at earlier times (Bety et. al, 2004). It has been shown that geese that arrive earlier have better reproductive success than late-arriving geese. However, there are costs associated with arriving too early (Bety, 2004). These costs include harsh conditions in early spring that increase adult maintenance costs, less food availability, and increased predation (Bety et. al, 2004). It is shown that there is a benefit to arriving a few days earlier than average, but too early can decrease reproductive probability (Bety et. al, 2004). This indicates that birds that arrive at their breeding grounds much earlier than average have decreased fitness.

This table shows the changing in migration times and arrival and departure dates of snow geese. Source: Bety et. al, 2004

Climate change and the early arrival of snow geese to their breeding grounds have caused an increase of nest and adult predation and new predators are also a threat. Rockwell and Gormezano (2009) studied the effects of climate change on the arrival of polar bears on the nesting grounds of snow geese. The earlier melting of ice in the Hudson Bay has caused polar bears to come to shore earlier and reduced their predation on ringed seals. this has caused them to have a nutrient deficiency (Rockwell and Gormezano, 2009). This causes increased predation to snow goose nests, as the eggs provide the nutrients that the polar bears are lacking. These nests are easily preyed upon by polar bears and if this trend continues to increase, many snow goose colonies could suffer massive declines (Rockwell and Gormezano, 2009).

This graph shows the overlapping and advancing of snow goose nesting times and the arrival times of polar bears to nesting grounds. Source: Rockwell and Gormezano, 2009

These factors could eventually lead to a crash in snow goose populations as their resources could become depleted, their fitness levels drop, and they are at greater risk of predation. However, management actions are being implemented to decrease populations to sustainable levels. Changes in hunting regulations, as well as governmental intervention, are being used to control the overpopulation of snow geese. Historically, snow goose hunting seasons

Spring snow goose hunting seasons are one-way overpopulation is being managed. Source: Northern Skies Outfitters

have been during the fall migration and strict regulations were implemented to protect from overharvesting of populations. Now, spring seasons have opened in the United States and Canada to increase harvest numbers in snow geese (Lefebvre et. al, 2017). These seasons also reduce restrictions on hunting, such as allowing more than three rounds of ammunition to be loaded in a firearm at a time, allowing electronic calls and baiting, and an allowing more birds to be harvested ( Lefebvre et. al, 2017). The spring conservation harvests have had an impact on the reproductive ability of snow geese, as clutch sizes were smaller, laying date was later, and a decrease in reproductive activity. These effects were shown to be caused by the energy decreases and foraging decreases due to the disturbance caused by spring hunting (Lefebvre et. al, 2017).

Also, governmental agencies have enacted management plans to help control the populations and protect habitat. The U.S. Fish and Wildlife Service in conjunction with the Canadian Wildlife Service released a management plan in 2007 to control snow goose populations. Some of the efforts include nest and egg destruction, reproductive inhibitors, and mechanical, biological, and chemical control. The destruction of eggs and nests has little evidence of success in population controls, as geese will often lay additional eggs if the first clutch is destroyed (U.S. Fish and Wildlife Service, 2007). However, reproductive inhibitors such as conjugated linoleic acids have been observed to reduce eggs hatch rates (U.S. Fish and Wildlife Service, 2007). Mechanical control such as shooting and trapping have also been effective in reducing populations. Biological controls such as predators are effective at population control but may have unforeseen impacts on the rest of the habitat. Chemical controls such as poisons in bait are also being used to control snow goose populations but may cause mortality in unintended species (U.S. Fish and Wildlife Service, 2007).

The Canadian Wildlife Service has made management plans in conjunction with The U.S. Fish and Wildlife Service. Source: USGS

The U.S. Fish and Wildlife Service have made management plans in conjunction with the Canadian Wildlife Service. Source: U.S. Fish and Wildlife Service

The overabundance of snow goose populations is due to climate change and the ability of snow geese to thrive in many conditions, including warmer than average conditions. Snow geese continue to destroy their habitats and cause widespread destruction of the vegetation in the Hudson Bay region. Although management actions have been successful in slowing the growth of these populations, monitoring of these populations is crucial as snow geese can easily take advantage of changing environments and resources, and equilibrium numbers are challenging to maintain.






Aubry LM, Rockwell RF, Cooch EG, Brook RW, Mulder CPH, and Koons DN. (2013). Climate change, phenology, and habitat degradation: drivers of body condition and juvenile survival in lesser snow geese. Glob. Ch. Bio. 19:149-160.

Bety J, Giroux JF, and Gauthier G. (2004). Individual variation in timing of migration: causes and reproductive consequences in greater snow geese (Anser caerulescens atlanticus). Behav. Eco. And Sociobio. 57(1):1-8.

Humburg DD. (n.d.). Light goose dilemma: despite increased harvests, populations of these arctic-nesting geese continue to grow. Ducks Unlimited.

Lefebvre J, Gauthier G, Giroux JF, Reed A, Reed ET, and Belanger L. (2017). The greater snow goose Anser caerulescens atlanticus: managing an overabundant population. Ambio 46(2):262-274.

Peterson SL, Rockwell RF, Witte CR, and Koons DN. (2013). The legacy of destructive snow goose foraging on supratidal marsh habitat in the Hudson Bay lowlands. Arct. Antarct. and Alp. Res. 45(4):575-583.

Rockwell RF, and Gormezano LJ. (2009). The early bear gets the goose: climate change, polar bears, and lesser snow geese in western Hudson Bay. Pol. Bio. 32(4):539-547.

U.S. Fish and Wildlife Service. (2007). Alternatives. In: Final environmental impact statement: light goose management. U.S. Depart. of the Inter. pp 9-25.