New England is a sea duck's winter wonderland

“Flapping in a winter wonderland”, slightly alter the lyrics to Richard B. Smith’s Winter Wonderland and now we’re talking sea ducks. If you’ve had the pleasure to be on a boat off the shores of New England in the not-so-balmy winter months then you have probably gazed upon rafts comprised of thousands of sea ducks bobbing in the waves. These ducks inhabit our coasts during the winter to take advantage of plentiful food sources while their more northern breeding areas are covered in ice, but just where do these birds go during the rest of the year and what routes do they take to get there? Dustin Meattey, a recently graduated masters student from the University of Rhode Island, partnered with three other wildlife agencies to answer that very question.

White-winged Scoter Movements and Habitat Use in Southern New England, original article published in RI DEM Hunting and Trapping 2018-2019 Regulation Guide

Sea ducks are some of the most prized waterfowl species for duck hunters, wildlife photographers, and birders. The coastal waters and offshore environments in southern New England provide crucial winter habitat for several species including Common Eiders, all three species of scoters (Black, White-winged, Surf), and Long-tailed Ducks. Over the past several decades, population declines of many sea duck species have highlighted the need for a better understanding of their habitat preferences, migration patterns and timing, and linkages between important geographic areas throughout their life cycle. Reasons for these declines remain poorly understood, but habitat conditions and disturbance on the wintering grounds may have carry-over effects impacting annual survival and breeding productivity during subsequent seasons. Because sea ducks spend much of their annual cycle in non-breeding areas where human-induced threats are often greatest, understanding habitat use on their wintering grounds is crucial for conservation planning. As the development of offshore wind power moves closer to large-scale implementation in the northeastern United States, particularly in areas used by sea ducks during winter, identifying important habitats used by wintering sea ducks informs the planning process and helps avoid displacement of sea ducks from preferred habitats.

White-winged Scoter with a satellite transmitter,  Photo credit:  Josh Beuth

White-winged Scoter with a satellite transmitter, Photo credit: Josh Beuth

One species of sea duck that inhabits New England coastal waters during the wintering period is the White-winged Scoter (Melanitta fusca). White-winged Scoters are a long-lived sea duck species that winters along both the Atlantic and Pacific coasts of North America, with increasing numbers also wintering on the Great Lakes. White-winged Scoters nest throughout the interior boreal forest from Alaska to central Canada, with geographically separate eastern and western populations, although some studies have suggested that birds from Atlantic and Pacific coasts may overlap on the breeding grounds. Like most other sea duck species, White-winged Scoters have apparently experienced a long-term population decline throughout the last half-century.

Researchers from Rhode Island Department of Environmental Management (DEM), University of Rhode Island, Biodiversity Research Institute, and the Canadian Wildlife Service partnered together between 2015 and 2018 to study the movement ecology of White-winged Scoters.  We deployed over 50 satellite transmitters in adult females on their wintering grounds in southern New England and at a molting area in the St. Lawrence River Estuary in Quebec. We were able to follow the movements of many individuals for over two years, as they traversed thousands of miles between wintering areas on the East Coast to breeding grounds across the northern boreal forest from Quebec to the Northwest Territories of Canada, on their return migration to important molting and then wintering areas, and for some back again to the breeding grounds.

Fig. 1. Estimated probability of use by adult female White-winged Scoters in nearshore and offshore waters in southern New England based on movements of satellite-tagged birds. For information on the most current wind energy areas, visit  BOEM: Offshore Wind Energy

Fig. 1. Estimated probability of use by adult female White-winged Scoters in nearshore and offshore waters in southern New England based on movements of satellite-tagged birds. For information on the most current wind energy areas, visit BOEM: Offshore Wind Energy

The data gathered from these birds allowed us to calculate the size and habitat characteristics of winter home ranges, and to identify specific areas in southern New England during winter that were preferred by White-winged Scoters (Fig. 1). Our results suggested that offshore sites predicted to be most used by scoters had minimal overlap with currently leased and proposed wind energy areas in southern New England (shown in blue). However, many birds made long-distance flights throughout the winter between areas like Montauk Point, NY and the Nantucket Shoals south of Nantucket Island, therefore they were likely often crossing wind energy areas as they moved between their preferred sites. This suggests that future wind energy development in the currently proposed lease areas could act as a deterrent or barrier to these important within-winter movements.

Using the movement data from these scoters, we were also able to identify and document their primary migration routes between breeding and wintering areas and the timing of these movements (Figs. 2, 3). This information is important for biologists responsible for designating hunting seasons and for protecting key areas used during migration, and for others responsible for managing offshore wind farms and other potential sources of disturbance. White-winged Scoters wintering in coastal New England bred throughout northern Canada from northern Quebec to the Northwest Territories. After leaving the breeding grounds, scoters underwent a month-long wing molt primarily in James Bay and the St. Lawrence River Estuary before continuing their fall migration back to their primary wintering grounds in southern New England. An important finding from this research was that migration timing was consistent among all birds in our study, regardless of where they bred or molted, and regardless of what route they decided to take. Essentially, the eastern portion of the continental White-winged Scoter population seems to function as a single, continuous population with little evidence of any geographically distinct sub-populations. This suggests that our current harvest of White-winged Scoters should not disproportionately target any particular segment of the population.

Our hope is that this project provides helpful information to policy makers, developers, and biologists to best conserve and manage this important species. This study was part of the Atlantic and Great Lakes Sea Duck Migration Study, a multi-partner collaborative project initiated by the Sea Duck Joint Venture.

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About the author:
Dustin Meattey studied Spatial ecology of sea ducks in the Scott McWilliams lab at the University of Rhode Island and is currently a wildlife biologist with Biodiversity Research Institute.

Nesting up North: the Ups and Downs for migratory songbirds.

If you’re an avid follower of the “Living with Change” blog (and let’s be honest: who isn’t?), you have probably read a lot about bird migration. There are so many incredible facets to this topic, as covered wonderfully by Clara Cooper-Mullin in her recent post. The great thing about bird migration in particular is how extreme it can get. A large portion of the songbirds that breed in North America winter somewhere in the tropics and then migrate to lush breeding areas throughout the lower 48 and southern Canada. We know the basic advantages of migration for birds, chief among them the chances for more food and nesting resources. But what about the birds that go way up north? Why go the extra mile (in this case, the extra 1,000 miles)? What about this far northern environment is so enticing to many migratory species? And what kind of changes is the north experiencing that could greatly impact these animals?

Arctic Tern, perhaps the most dramatic example of extreme migration to capitalize on abundant resources up north. Manitoba, 2018  Photo: Steve Brenner

Arctic Tern, perhaps the most dramatic example of extreme migration to capitalize on abundant resources up north. Manitoba, 2018 Photo: Steve Brenner

I was fortunate to study this very topic while working in the Canadian subarctic this past summer outside of Churchill, Manitoba. This research camp has been studying nesting colonies of Lesser Snow Geese for 50 years, and has discovered a plethora of fascinating environmental, climate, and population dynamics that have impacted the tundra significantly. The most dramatic and significant impact on this ecosystem has been the habitat degradation caused by booming snow goose populations (think Canada geese pooping and eating people’s lawns but way worse). Additionally, climate change is steadily altering the landscape on the tundra as well. Willow and birch shrub continue to creep north each year, changing habitat from grassy tundra with minimal willow to shrub-dominated river and tidal zones. 

The willow shrub, tidal zone, and nearby Hudson Bay outside of Churchill, Manitoba.  Photo: Steve Brenner

The willow shrub, tidal zone, and nearby Hudson Bay outside of Churchill, Manitoba. Photo: Steve Brenner

My research interest was focused on the impacts of this habitat degradation to the community of songbirds that nest in these areas. Specifically, I was interested in the nesting success and nestling growth rates of Savannah Sparrows that bred in two different northern habitats: areas degraded by geese and healthy coastal areas that have not been impacted by snow geese. Savannah sparrows are the perfect species to study in such environments. They are a relatively generalist species when it comes to nesting sites, they have multiple populations that stretch from the arctic to the Midwestern U.S., and their breeding behavior has been studied on the tundra, in grasslands, and in coastal areas of the northeast. 

Savannah Sparrow on the tundra. Manitoba, 2018.  Photo: Steve Brenner

Savannah Sparrow on the tundra. Manitoba, 2018. Photo: Steve Brenner

Given this rather wide distribution, Savannah sparrows are an excellent species to examine some of the different breeding strategies across latitudes; namely the reason to nest so far north. Apart from plenty of insects and a bounty of nesting sites, there are a few other advantages to nesting way up north, as well as some unique challenges.

Challenge: Breeding season is shorter.

If a songbird decides to nest further south, the breeding season begins around mid-May, with insect (food) abundance peaking right around when baby birds begin to hatch. Additionally, as the weather remains favorable and if insect levels are normal, the chance for attempting multiple clutches is better the further south you are. Nestlings can take a bit more time to develop, and to some extent this is limited by the amount of daylight parents have to forage for their young, as well as the extent of insect populations and competition in a given area.

As you probably already know, things are kind of cold on western Hudson Bay. And it stays colder for longer. I arrived to camp on May 27th. This is what it looked like.

The research camp in late May. Snowy, eh? Manitoba, 2018.  Photo: Steve Brenner

The research camp in late May. Snowy, eh? Manitoba, 2018. Photo: Steve Brenner

Now, songbirds can handle snow for a little while, but they can’t nest in it. Also, with no leaves and no warmth, there is a lack of adequate cover for a nest and most importantly, no bugs. Songbirds are pretty flexible when it comes to waiting on the right conditions to begin building nests and laying eggs. But they can’t wait forever, and on top of that, Savannah Sparrows had to complete one helluva migration to make it to northern Manitoba. Adults that arrive on the breeding grounds have to establish a territory and find a mate. But with minimal food and a snow-covered landscape, mating takes a bit of a back seat to finding food and personal maintenance.

One of the study sparrows, biding time while the snow melts in mid-June. Manitoba, 2018.  Photo: Steve Brenner

One of the study sparrows, biding time while the snow melts in mid-June. Manitoba, 2018. Photo: Steve Brenner

Average nest hatching date in 2018 was July 8th. While this number is likely to change from year to year, it won’t change by much. For Savannah Sparrows that nest in places like coastal Maine, the first nests hatch around first week of June (Wheelright and Rising 2008). This means many birds south of Churchill will have fledglings before eggs even hatch up north. This delayed timing has other implications as well. Most songbirds in the lower 48 will have multiple nesting attempts, particularly if the first one fails. Say a squirrel or blue jay ate your first clutch of eggs on Memorial Day. Oh well. You still have the whole month of June and July to build a new nest, lay some more eggs, and raise some fledglings. But if you nest way up north and didn’t lay your eggs until the end of June, there is a much bigger time crunch. Depending on when the first clutch failed, you may just run out of time to make another nest. Sure, you can try to re-nest and lay eggs in mid-July. But given the roughly three weeks needed to lay, incubate, and fledge, birds are running into a big problem with much less food available by mid-August and rapidly changing weather come September. 

Advantage: The days are longer, so growth is faster!

Yes, it certainly seems like a bummer to have only two months or so to raise your young. But what a two months! Average day length in June and July in Churchill is around 18 hours, with a few more hours added to the prolonged twilight periods. And there are WAY more insects on the tundra and edges of the boreal forest than there are in the forests and fields of the lower 48 (believe me, it’s like insect Armageddon up there).  So mangia mangia!! Similar species nesting in Rhode Island only have at most 14-15 hours of daylight to feed and forage during the summer. Birds up north have more time and more food available. This adds up to nestlings getting fed more often than their counterparts down south. This also means young spend shorter times in the nest, which is usually the most vulnerable and dangerous time for young songbirds. They grow up so fast…  

Sometimes an advantage, sometimes a disadvantage, but always dangerous: Nest Predators

Seems like anywhere you go as a tiny songbird building a nest and laying eggs, there will be some critter that thinks your eggs are delicious. Nest predation just goes with the territory of being a songbird. 

At first blush, the sub-arctic tundra has a more favorable lineup of would-be nest predators. Predators like squirrels, chipmunks, raccoons, jays, magpies, cooper’s hawks, and even deer are abundant at lower latitudes (and all will eat an egg or nestling if given the chance).  Also, there is a wider variety of nesting songbirds down south, so it behooves predators to cue in on songbird activity. Up north, squirrels, chipmunks, and most other small mammals are a no-show. Canada Jays only hang out near the boreal forest and aren’t found on the tundra. Seems like a win, right?

While the variety of nest predators doesn’t quite match that of the south, danger still abounds. Short-tailed weasels roam the area and are expert nest robbers. Ravens might not spend too much time worrying about little songbird eggs when there are shorebird and duck nests to be had, but you never know with corvids. And in some years, Arctic Fox make their presence felt on the tundra. In short: building a nest and laying some eggs always comes with risk.

So why study Growth up north?

Despite the extra time and energy needed to make it up north, and despite the shorter breeding season, the Savannah sparrows of Churchill (and even further north!) have successfully carved out their little slice of heaven in the tundra scrub. What remains to be seen is how the ever changing northern climate and additional goose degradation has impacted their breeding success, specifically the growth of their young.

Goose degradation has already been shown to be detrimental to Savannah Sparrow nesting density in Churchill. My questions were pretty basic but nonetheless important in regards to breeding success. Are individuals able to successfully nest and fledge young in both degraded and non-degraded sites? The implications of this are obvious: if Savannah sparrows can’t fledge nestlings in one site over the other, these degraded areas of tundra and coastal scrub become ecological traps for songbirds. 

If birds can successfully raise and fledge young, will there be any differences in the growth and development of their young? Growth and development is extremely important in the life cycle of a songbird. Not only does it impact the ability for a bird to even leave the nest and survive on its own without parents, young birds in northern environments must be able to reach the proper body condition by fall to complete (you guessed it!) their first critical migration down south.

As we start to answer these and (hopefully) many more questions surrounding growth, development, and success in northern climates, we will be able to see a clearer picture of how shifting environments impact northern ecosystems and the birds that inhabit them.  


———Works Cited———

Wheelwright, N. T. and J. D. Rising (2008). Savannah Sparrow (Passerculus sandwichensis), version 2.0. In The Birds of North America (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi-org.uri.idm.oclc.org/10.2173/bna.45


 

About the author:
Steve Brenner studies the impacts of habitat management on avian spatial ecology in the Scott McWilliams lab at the University of Rhode Island

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Its fall, so its time to chat about songbird migration in New England!

Migration is a particularly vulnerable time of year for songbirds. Birds are facing novel habitats, exhausting exercise, and are encountering more predators and human modified environments. Why do some bird species take this risk? Birds are in search of predictably abundant resources to eat through the winter, and on their breeding grounds food becomes scarce and highly coveted as temperatures decrease . Birds also spend a large chunk of their annual cycle migrating (see below for a Blackpoll Warbler’s annual cycle to see what I mean). So studying how birds are making these journeys, what they are eating on the way, where they go, when, and in what direction is important and can lead to better decisions about how to help them on their way.

A Blackpoll Warbler’s annual cycle: notice how much time each year it will spend traveling between breeding and wintering locations

A Blackpoll Warbler’s annual cycle: notice how much time each year it will spend traveling between breeding and wintering locations

Understanding how physiological condition (how much fat and/or antioxidant capacity a bird is able to store) influences a bird’s behavior can help us to better understand their needs during this susceptible time. Further, physiological and behavioral actions during spring and fall migration can have consequences that spill over into the winter or breeding seasons (called carry-over effects). We are in the midst of a manipulative field experiment that is trying to tease apart whether fat stores and antioxidant stores are important drivers of decisions birds make during their travels.

But before I start talking just about birds and how cool they are, I want you to take a second and think about an animal that embodies athleticism to you. Did you think of the sprinting cheetah, or the fast swimming sailfish, or maybe the remarkable dive of a hunting peregrine falcon? Well, of course you would be right! All those species are incredibly fast athletes.

However, when I think of any sort of endurance athleticism in the animal world, I tend to think of animals that are migrating – especially migratory birds. Every year thousands of birds make long migrations around the globe, moving from areas of declining resources to areas of abundant resources. And, these birds fly hundreds to thousands of miles in the process, which is a crazy feat of endurance exercise. Among migrating birds, there are definitely some rock stars. The Arctic Tern is pretty famous (to us bird people) since it flies almost 60,000 total miles during migration. As is the Bar-tailed Godwit that migrates nonstop from Alaska to New Zealand or Australia, covering more than 6,000 miles in about 8 days of continuous flying (which is exhausting for me even to contemplate). However, although some birds are able to migrate in one flight, birds have many different strategies to help them travel these enormous distances and there is a lot of variation in how these journeys are made.

First, there could be variation in the routes a bird may take - in North America a songbird breeding in the arctic and wintering in South America may take a completely overland and direct route to get there, or they could fly east and then down the coast and across the gulf or straight across the ocean.

Possible migratory routes birds can take on their way south.

Possible migratory routes birds can take on their way south.

Second, most migrations are not non-stop flights, and therefore, during migration, short periods of endurance flight are traded off with periods of feeding and rest at stopover sites. There may be many stopovers on a bird’s migration from their breeding location their wintering location.

Migration = short endurance flights punctuated with longer periods of rest and refueling with native berries and fruits at stopover sites along the way

Migration = short endurance flights punctuated with longer periods of rest and refueling with native berries and fruits at stopover sites along the way

Migratory stopover sites are crucial for birds to rebuild energy stores, and the time a bird spends on a stopover can influence the timing and success of its overall migration. Additionally, during flight, birds have an elevated metabolism leading to an increase in the production of a byproduct we call reactive species. Reactive species can cause damage to cells, tissues, or DNA if not balanced by antioxidants**. Luckily for the birds, during the fall, there are a ton of seasonally abundant fruits around that are full of dietary antioxidants and fats. Birds that normally eat insects during the rest of the year generally switch to eating these fruits during migratory stopovers. However, the quality of stopover sites and the amount of fruit available to birds varies among sites and across a migratory season. We were curious about whether birds that have more fat and/or antioxidants in their diet can spend less time on a stopover site, and whether they are more likely to depart in a seasonally appropriate (southerly) direction.

To examine these differences, we headed out to Block Island, Rhode Island, an offshore stopover site that is popular for migrating birds and performed a field experiment. We caught four species of birds (Blackpoll Warblers, Hermit Thrushes, Red-Eyed Vireos, and Myrtle Warblers) that varied in their migration patterns, and manipulated their physiological condition.

Looking at multiple species of birds will allow us to compare how important condition is for birds with different migration strategies (land-based vs. over the sea) and migration distances (short vs long). Myrtle Warblers (Setophaga coronata coronata), migrate shorter distances than many of the other species passing through Block Island in the fall, and winter farther north than any other wood warblers. Hermit Thrushes (Catharus guttatus) are medium distance migrants that travel from Block Island to winter in the southern United States and Central America. Red-Eyed Vireos (Vireo olivaceus) are long-distance migrants that regularly stopover on Block Island during the fall. After leaving Block Island they are more likely to migrate overland until they reach the Gulf of Mexico, which means they will probably stop many more times as they travel south. In contrast, after leaving Block Island in the fall, Blackpoll Warblers (Setophaga striata) make an insane journey out across the open ocean for 3-5 days of non-stop flight before reaching a wintering destination in the Caribbean or South America.

We used mist nets to capture these four species and and then kept them in an outdoor aviary for a couple of days to manipulate their physiological condition. Once caught, we either gave the birds a diet rich in fat and/or antioxidants (we called this the ad lib diet) or a diet without extra fat and/or antioxidants (we called this the maintenance diet since birds, well, maintained the weight that we caught them in). We wanted to fatten the birds up (ad lib diet) and give them a lot of dietary antioxidants so that they were in better condition to simulate birds on a stopover site that would be abundant with fruits. We contrasted that diet treatment with the maintenance diet to simulate birds that wouldn’t have as much access to fruits on stopover. We predicted that birds that were able to stuff themselves with fat and antioxidants would be in better condition and would be more likely to migrate sooner and, potentially, reach their wintering grounds sooner than birds that were unable to do so.

We also took blood samples to look at their antioxidant capacity. A bird’s blood can tell us all sorts of levels of circulating antioxidants or other metabolites, kind of like when you go get checked for your cholesterol at the doctor. We predicted that birds given dietary antioxidants would have increase their circulating levels of antioxidants during captivity. After several days in captivity, birds on the fat rich diet had gained a lot of fat, where birds on the maintenance diet were still in the condition that we had caught them in. We then attached small radio-transmitters called Nanotags to these birds. Each nanotag sends out a unique signal every 10 seconds that can be picked up passively by receiving stations in the MOTUS network. We built one of those receiving stations on Block Island, but it was a part of the network of towers that extends from Canada down into South America. If any of our tagged birds fly along the Atlantic flyway then there is a good chance we’ll know about it.

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Automatic Receiving

Station on Block Island

This 40ft tower is a part of the MOTUS network and will passively pick up the signals from any Nanotag within it’s range

Nanotags will help us determine whether birds on an ad lib diet or one that was given dietary antioxidants can leave Block Island sooner and in a more seasonally appropriate direction than those on the maintenance diet or ones not given dietary antioxidants.

Linking behavioral decisions and physiological condition of songbirds together can help us to understand the types of habitats and food resources different bird species need on stopover sites. In turn, that could help to determine how we can best conserve those areas, or how we can restore them by planting native fruits and berries (see this helpful guide on what to plant!) to help these incredible athletes on their way.


**Antioxidant Definition: Animals have a multifaceted antioxidant system made up of endogenous antioxidants, micromolecular sacrificial molecules and dietary antioxidants that work synergistically to protect against oxidative damage (from those pesky reactive species). For birds in migration, the relationship between reactive species production, antioxidant protection and oxidative damage is not straightforward, and various aspects of the antioxidant system may respond differently depending on the type of damage, the duration of flight or the physiological state a bird. Dietary Antioxidants: Antioxidants produced by plants and consumed by animals in their diets. The two broad classes of dietary antioxidants include lipophilic antioxidants (vitamin E or carotenoids) and hydrophilic antioxidants (vitamin C or polyphenols). In this study we specifically examined polyphenols.


 
About the author:   Clara Cooper-Mullin  is a PhD student studying the impacts of diet and body condition on songbird migration the  Scott McWilliams lab  at the University of Rhode Island

About the author:
Clara Cooper-Mullin is a PhD student studying the impacts of diet and body condition on songbird migration the Scott McWilliams lab at the University of Rhode Island

 

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What can we learn from animal home ranges?

Integral to all of our daily, monthly, and yearly activities is the locations where we perform our tasks, be they recreational, professional, or personal maintenance. We don’t necessarily have to define ourselves based solely on our locations, and even though Dave Matthews would probably disagree, where we are can certainly provide plenty of information about our lives.

Birds are no different. They go to certain locations to sleep. They go to certain locations to eat breakfast. And even though birds don’t have an economy or traditional ‘jobs’, they still have work to do. Thus, if we can figure out where an individual bird is, and better yet, why that individual is there, we can start to piece together the rich tapestry that is the life of a bird. And with more information about where birds go and how they get there, conserving habitat and populations becomes that much easier and more effective.

A Prairie warbler surveys his breeding territory. Pennsylvania, summer.  Photo credit: Steve Brenner

A Prairie warbler surveys his breeding territory. Pennsylvania, summer. Photo credit: Steve Brenner

            First big point to establish: this is all about tracking individuals and then using that spatial information to answer a variety of questions about birds. Tracking animal movements at the population or species level is possible, albeit with slightly different methodological frameworks, but we can save that for another post. There are many ways to track individual birds, and the methodology is usually defined by the questions you want to answer and the technology available. This is quite a robust topic with a deep history, but alas, we must contain the ever-growing urges of scientific curiosity bubbling inside and focus on the overall purpose of tracking individuals. What kind of information can we gain, and what can we say or do with that information?

            Let’s look at one of the basic and fundamental measurements in spatial ecology - an individual’s home range. The simplest definition of a home range is the space where an animal lives. Think of the daily routine example from above. Where we sleep, eat, and work exists within a certain space. Usually this space is contained within a town or city, and within that space would be your house, your office, your favorite places for recreation. Likewise, a bird’s home range is the space that contains the locations where it forages, nests, preens its feather, and sleeps.

            To generate a home range, the first things we need are the locations in space and time of an individual (think GPS points on a map). Next, we need to choose a period of time we are interested in. For migratory birds, this could be a variety of periods throughout the year that each encompass different ecological behaviors and have different implications. For example, the breeding season, roughly May-August for North American birds, would be the time to construct a classic home range that contains a nest location, feeding areas, and locations for protecting young from predators.

Nestling Dark-eyed juncos, hoping their parents picked a safe nest location. Arizona, summer.  Photo credit: Steve Brenner

Nestling Dark-eyed juncos, hoping their parents picked a safe nest location. Arizona, summer. Photo credit: Steve Brenner

To properly construct a home range, we need to make sure we have enough locations that we are gathering (or sampling from) that are representative of the bird over different times of the day and over the entire period of interest. Once we have our representative locations, we can plot them on a map and build the home range. But enough with the words, Steve, give us an example!

I’ve been studying towhees for the past two years in an effort to assess the effectiveness of statewide early successional/young forest management strategies for songbirds. Towhees are perfect representative of young forest or shrubland birds. Think of all the thorny, scrubby, bushy places you avoid on a daily basis…this type of habitat is perfect for towhees, and it’s in short supply in southern New England. Gathering spatial and nesting data on towhees and other shrub birds in Rhode Island will help us understand how (and if) these animals are using state-managed forests.

Male Eastern towhee, looking sharp and ready to provide spatial data with his new transmitter. Rhode Island, summer.  Photo credit: Steve Brenner

Male Eastern towhee, looking sharp and ready to provide spatial data with his new transmitter. Rhode Island, summer. Photo credit: Steve Brenner

Let’s look at the locations of an adult male Eastern towhee between June and August 2016 in Rhode Island. This individual was tracked after he successfully fledged 2 young, and was subsequently caring for his fledglings. Here are some of his GPS locations mapped out.

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Already this is pretty cool to visualize. Just from seeing his points in context with aerial imagery is neat on its own. Also, the imagery provides a general context for the type of forest towhees are hanging around. But let’s create his home range and see what else we can find out. The simplest way to do this is by a method called ‘Minimum Convex Polygon”, or MCP. Essentially, this entails drawing the smallest box possible around all of our sampled points.

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Cool! Already we can look at this map and say some things about this bird’s life. For instance: the size of this polygon is just about 1 hectare, which is roughly the size of a football field. Thus, this particular bird seemed to consistently spend a lot of time within a hectare-sized area while his young slowly grew up over the summer. But this whole straight-lined polygon thing seems a bit…unnatural. What are the odds that this towhee didn’t stray outside the blue lines on the map, or put another way, the likelihood the summer home range of this bird doesn’t include space beyond these lines? Fortunately, scientists have devised other ways to estimate home ranges beyond MCPs. A common method to account for the likelihood of an animal occurring outside this arbitrary polygon is by using kernel density estimation, or KDE. These methods can be a little complex and depend on many factors including sample size (how many points did you gather per bird?), autocorrelation (the influence of one location on the next), and bandwidth estimators (for statistics!).

I know what you’re thinking: we have reached the section of the article filled with multi-syllabic words that sound like math and are intentionally complex, and the only people who understand this are folks that like tofu and listen to jazz. Fear not. The extremely short explanation of KDE is that by using the distances between the sample locations themselves, one can more accurately estimate the probability of space used by an animal, and thus build a better home range. So let’s rebuild this towhee’s home range using KDE.

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            Well isn’t this just a pretty looking bit of spatial data! The size of this polygon is 2.8 hectares, which is much larger than the square box from earlier. But think about why this makes more sense. Giving the layout of this points, the odds that this bird wouldn’t use areas outside the GPS points I sampled it at are slim. These points are daily samples of one point in space - not direct minute-by-minute tracks of the bird, or even it’s path from one point to the next. Thus, this type of home range estimation takes this fact into account and by the magic of statistics you get this purple polygon. With a measurement of home range, we can compare this bird’s movements to other towhees that are raising young, or even to other towhees but during different stages of the life cycle (for example: does the home range size between the post-fledging period and the nesting period? I don’t know, but that’s a great question for future research!)

Think about the habitat/environmental questions we can answer with this home range. What if I wanted to know how much towhees utilized previously managed forest clearcuts? Well, first I can add this GIS layer that outlines areas that were previously managed by the state.

Tmgmy.png

Sweet! Then I could overlap with the home range, and calculate a quick percentage (~65%). Seems like this critter was happy to use a regenerating clearcut to raise his young, which makes a whole lot of sense. Early successional forests are full of densely packed shrubs and young trees. This provides excellent cover for vulnerable, recently fledged baby birds.

A fledgling towhee, wondering if it's about to be fed or eaten. Rhode Island, summer.  Photo credit: Steve Brenner

A fledgling towhee, wondering if it's about to be fed or eaten. Rhode Island, summer. Photo credit: Steve Brenner

We could also overlay the different type of forests in and around this bird’s home range in order to get a better sense of the immediate landscapes around towhees.

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As in most research, if we can gather similar data and create home ranges for a larger sample of towhees, we can more confidently use this data to answer some really interesting questions about our ecosystem. Think of the possibilities!

-Does proximity to developed areas or edges influence survival?

-Do females use more or less space, or do birds with our without young use more or less space?

-Does distance to other managed forests impact spatial movements?

The possibilities are endless! These are the types of questions I’ve been working on with these little songbirds, and with a rapid increase in tracking technologies, all sorts of spatial questions are starting to be answered and will be addressed in the near future. But a home range is always a good place to start!

(All maps were created with ArGis.)

 

About the author:
Steve Brenner studies the impacts of habitat management on avian spatial ecology in the Scott McWilliams lab at the University of Rhode Island

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Bring on Spring! Animal physiology is as transformative as our seasons

Physiology is the study of how animals work and perform everyday functions like breathing, walking, and maintaining a normal body temperature. In many species, animal physiology responds to environmental conditions including the amount of available water, the temperature, and the time of year. A general rule is that when the environment changes then animal physiology responds!

It is important to note that changes in physiology and behavior often occur together. For example, a bird readying itself for migration will eat a larger amount of food in order to double the size of their fat stores that are crucial for providing fuel during long-distance flight. This behavior would be impossible if their physiology was inflexible, but luckily they remodel their digestive system to cope with processing all of this food!

An alternative tactic that animals use to fit into their environment is that they change only their behavior so that they experience a constant set of environmental conditions, and as a result they avoid changes in their physiology. Aquatic turtles use this strategy to keep their body temperatures fairly constant by switching between basking themselves in the hot sun and plunging themselves in the cooler water.

Whether or not animals change their physiology, their behavior, or their physiology and behavior depends on the species and on their environmental situation. For this post I'll summarize the types of changes in physiology that this blog will focus on!

An unfrozen wood frog ( Rana sylvatica ) found by a biology undergraduate student in Massachusetts, September 2017,  Photo credit: Kristen DeMoranville

An unfrozen wood frog (Rana sylvatica) found by a biology undergraduate student in Massachusetts, September 2017, Photo credit: Kristen DeMoranville

Physiology can change on a short-term timescale soon after their environments have changed, and these changes are reversible. This happens to us! Standing outside on a cold winter day in thin mittens, it only takes about 30 minutes to notice our hands are cold and beginning to hurt. In this situation, our blood flow has been rerouted to our center to keep our important organs warm. During the winter in North America a specific species of frog, the wood frog (Rana sylvatica), buries themselves beneath the soil in preparation for freezing temperatures. These frogs are unable to keep their body temperatures high enough so that their organ systems could properly function. These frogs embrace that shortcoming and allow their bodies to freeze nearly solid immediately as ice forms around them in order to survive the cold. Special physiological adaptations protect their organs during this freeze and help them to completely recover as soon as the temperatures warm and ice disappears!  The Dr. Richard Lee & Dr. Jon Constanzo lab investigates the physiology of these amazing frogs. An overview of Dr. Lee & Constanzo's research can be found here.
Spring is here and wood frogs are emerging from their frogsicle forms NOW! If you are in Canada or eastern North America then keep your eyes peeled and ears open.

A banded male North American cardinal ( Cardinalis cardinalis ) in Rhode Island, April 2018,  Photo credit: Steve Brenner

A banded male North American cardinal (Cardinalis cardinalis) in Rhode Island, April 2018, Photo credit: Steve Brenner

Animal physiology can change on a long-term scale either days, weeks, or months after their environments have changed, and these changes are reversible. We can relate to this too! Taking a long walk on the first scorching day of the summer we feel drained. After experiencing this heat day after day it seems easier to take this same walk in mid-summer. Our bodies adjust to the heat with repeated exposure, and as a result we can better endure hot weather! Songbirds that stick around for cold winters rather than migrate to tropical regions have to change their physiology so that they can stay warm enough to properly function and survive. Winter resident birds like the Northern Cardinal (Cardinalis cardinalis) keep warm by enhancing their ability to generate heat through a tactic similar to mammalian shivering, but without the muscle trembling that we experience. They also increase their fat and feather layers in the winter to improve insulation which is crucial for keeping that extra heat that they produce inside their bodies. These physiological adjustments do not happen after the first freeze or even with the first snowfall, rather it takes weeks at cold temperatures for birds to transform their bodies into fat, fluffy, heat generating machines. The Audubon society covers how birds stay warm in more detail here and Dr. David Swanson's lab focuses much of their research on cold hardiness.
Spring is here, and despite the recent snow, cold hardy birds like the Northern Cardinal and Black-capped Chickadee (Poecile atricapillus) are losing fat and shedding fluffy feathers in preparation for the breeding season!

 
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A hibernating 13-lined ground squirrel (Ictidomys tridecemlineatus) in Dr. Jim Staples lab at the University of Western Ontario, December 2015, Photo credit: Kristen DeMoranville

Animal physiology changes in repeating patterns either daily, monthly, or yearly under the control of an animal's internal biological clock (defined as the bodily components that keep track of time within an animal). Whether you are a night owl or an early bird, our nightly sleep habits are controlled by our biological clocks. Read more about how our biological clocks control sleep here
Mammals like the 13-lined ground squirrel (Ictidomys tridecemlineatus) are adapted to hibernate during harsh winters when temperatures are below freezing, days are short, and food is unavailable. The internal clocks of these mammals filter through the environmental cues (e.g., temperature, light levels, and food availability) to control physiology and make hibernation possible. Ground squirrels lower their body temperature (and actually feel cold to the touch! See above picture) and slow their metabolism* (defined below) so that they are barely using or producing any energy. This means that their heart rates drop from 200 beats per minute to 20 beats per minute. Their biological clocks use similar environmental cues to stimulate their metabolism and rouse them from hibernation. National Geographic gives more overview about hibernation here, and Dr. Jim Staples investigates the metabolism of hibernating ground squirrels.
The onset of Spring is inciting hearts to flutter and, as Owl would explain to Bambi and Thumper, squirrels are twiterpated! If you live central North America then go searching, and don't forget to count their lines!

Animal physiology responds to environmental changes either on a short-term scale, long-term scale, or periodically in a repeating pattern. These changes in physiology can be difficult to observe firsthand. Although, behavioral changes can often act as a flag that alerts us to unnoticeable changes within an organism. Next time that you observe a behavioral change in one of your favorite critters I challenge you to think about the types of physiological adjustments that your animal might require to make that behavioral change possible. I'll review this post's comments in one week to see how well you all did with the challenge!

*Metabolism is a concept we will continue to revisit! This is how I like to think of the concept: All organisms require energy to perform their daily activities, and this so called fire for life is the product of chemical processes collectively referred to as an organism's metabolism.

 

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About the author:
Kristen J. DeMoranville is a Ph.D. student researching the effects of diet and long-distance flight on a migratory songbird in Scott McWilliams lab at the University of Rhode Island

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