trapping and tagging

Irruptions and Innovation

By Zoey Greenberg, Science Outreach Coordinator
Hawk Mountain Sanctuary

Stella, a snowy owl tagged by Project SNOWstorm earlier this year.

Stella, a snowy owl tagged by Project SNOWstorm earlier this year.

In 2007, Dr. JF Therrien deployed 12 transmitters on snowy owls on Bylot island in the Canadian Arctic. Snowy owls, like other raptors, can be difficult to monitor due to their territoriality and low densities. Arctic-breeding raptors typically establish nesting sites in remote locations, adding to the logistical dilemma of gaining insight into their life history traits, and the role they play within the Arctic ecosystem.

Satellite transmitters, citizen science, and long-term life history studies are extremely valuable tools that allow researchers to examine the movement ecology of birds, including snowy owls. Mixing and matching these tools can open doors to compelling scientific questions, and in the case of Therrien’s snowy owls, has resulted in papers covering a range of topics. New information on survival, reproduction rate, dispersal of adults, irruptions and winter movements are among recent Hawk Mountain publications that were made possible through this type of innovation. 

Two such papers were led by former conservation science trainees, in collaboration with others, including Dr. JF Therrien. These papers delved into the mystery of snowy owl irruptions, defined as the “massive movement of individuals over large distances, associated with large fluctuations in food supply.” Some of us have been lucky enough to see a snowy owl in Pennsylvania, on those rare winters when the birds venture further south than usual. I myself drove two hours to catch a glimpse, and I will never forget the sight of that owl hunkered down in the middle of a field, glittering in evening light. As I drove away, I couldn’t help but wonder; what brings them here?

Two primary hypotheses have been proposed to explain irruptions; the “lack-of-food” hypothesis suggests that snowy owls leave their normal wintering grounds because of food shortage in certain years. This implies that the snowy owls we see in Pennsylvania should be in poor shape, and likely close to starving. The alternative “breeding success” hypothesis instead links irruptive movements to a surplus of food on the breeding grounds.

A snowy owl that was spotted in a local PA field last year.

A snowy owl that was spotted in a local PA field last year.

Snowy owls specialize in lemmings, a prey resource that occurs in pulses, due to their population dynamics. One year there may be a plethora of lemmings scurrying around the tundra, the next year very few, due to high predation and other factors. Lots of lemmings means lots of chicks, which means lots more owls. The breeding success hypothesis implies that the reason we see snowies in Pennsylvania is because following a high lemming year, there are so many owls dispersing at the end of the summer that some young birds push south.

To add depth to our knowledge of irruptions, Teja Curk, a conservation trainee from 2016, assessed the body condition (mass relative to size) of snowy owls during both irruptive and “regular” years. Teja assessed body condition of snowies on both regular (Great Plains) and irregular (Northeaster North America) wintering grounds, to see whether the birds we see during irruptive years are, in fact, starving. She found that most owls (male, female, juvenile and adult) were in good shape during irruptive years and even discovered that body condition was better on the bird’s irregular wintering grounds. “Good shape” in this context varies depending on sex and age of the bird, however less than 2% of the owls approached the weight threshold that would deem them a starving bird. Her results provide support for the breeding success hypothesis.

Pablo Santonja and Irene Mestre, trainees from 2015, looked specifically at the age of the birds found south during irruptive years. Their results supported the same hypothesis, showing that the majority of owls (up to 90%) seen in eastern North America are juvenile birds, meaning they are less than 1 year of age. As with some other migratory species, the more dominant birds within a population don’t move as far. Adult snowy owls often out-compete young birds, so it makes sense that in a year where adults are laying up to 11 eggs, some of those young owls will need to leave to avoid competition from more successful, experienced adults.

Bylot Island, where the Hawk Mountain team tagged and tracked several snowy owls.

Bylot Island, where the Hawk Mountain team tagged and tracked several snowy owls.

This leads to an interesting point: perhaps these two competing hypotheses are not, as Teja notes in her paper, mutually exclusive. After a highly productive lemming year, many lemmings will be eaten due to a surge in predator numbers, and therefore the next year could produce low lemming numbers. If this happens, snowy owls could be forced to look elsewhere for food. So, it turns out, that both a surplus of food and a lack of food seem to play a role in the patterns of movement among snowy owl populations.

If you ask me, these papers are a beautiful example of the scientific method at work; formulating ideas, testing those ideas, and polishing the conclusions in pursuit of certainty. Hats off to our trainees and their collaborators for hard work and intriguing findings. Teja is currently at the Max Planck Institute for Ornithology in Germany pursuing a PhD. Pablo is living in Spain, and Irene is now returning from three years in Australia.

Both of these papers utilized a data set resulting from a 25 year-long study in which live snowy owls were weighed, sexed, and aged. Christmas Bird Count (CBC) was also a valuable asset in both studies. For those of you unfamiliar with CBC, every winter thousands of volunteers gather together on the same day, collecting bird records within a territory and submitting them to a database that provides an impressive summary of which birds were seen, where, and how many. These papers demonstrate the utility of both citizen science and long-term studies, and in a rapidly changing world, this cross-pollination of resources is critical. We are very proud of our trainees for their hard work, and grateful to citizen scientists around the globe who give their time to participate in the expansion of our raptor knowledge.

Gaining a holistic understanding of an ecosystem requires acknowledgment of moving parts within, not separate from, the whole. Hawk Mountain’s research is part of several collaborative efforts to better understand the role of snowy owls within the big picture, including Project SNOWstorm and the Bylot Island Ecological Studies and Environmental Monitoring.  

Future projects will include building a model that combines reproductive and mortality rates to assess population trends of snowy owls. This past August, three transmitters were deployed on chicks before they left their breeding grounds. Investigating the movement patterns of these birds will hopefully allow for a comparative look at owls throughout the Eastern tundra, Western tundra, and those in between.

Check out Project SNOWstorm’s website (including a blog written by J.F Therrien on the most recently tagged snowy owls in Barrow, Alaska, as well as interactive maps): projectsnowstorm.org/posts/tracking-young-snowies-in-the-arctic/

Trainee to International Conservation Pioneer

By Alfonso Godino, Research Associate
Hawk Mountain Sanctuary

The cinereous vulture was extinct in Portugal as a breeding species at the end of the 20th century, but in 2010 a new colony was established in Tejo Internacional National Park, in the eastern limit of the country and close to the border with Spain.

This colony now hosts 18 breeding pairs, and no studies were done before out of the annual breeding monitoring implemented by the Natural Park’s staff. Due to this lack of information, and being the main population in Portugal, our goal is to get information about the dynamic of this colony. Thus, the first step is to study the juvenile dispersion and the potential causes of mortality of this population.

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During the summer of 2018, eight nestlings were tagged with GPS-GSM transmitters, supported by Hawk Mountain Sanctuary and the Spanish electric company ENDESA. This support will continue during 2019, with the goal to increase the number of birds in this study and to get more accurate and representative information.

All this information will be shared with the Natural Park’s managers, with the objective to facilitate them the conservation and management of the colony, since all the nests of this colony are in private estates inside the protected area.

Alfonso with a tagged vulture outside of the HMS Acopian Center for Conservation Learning

Alfonso with a tagged vulture outside of the HMS Acopian Center for Conservation Learning

But how did HMS reach Portugal? During 2009, I was at Hawk Mountain as a trainee. I was an enthusiast in vultures’ conservation, and HMS offered to me the amazing opportunity to trap turkey vultures and to use wing tags for the first time in my life. But for me, the most impressive was to get access, for the first time in my life, to the huge amount of information about raptors in the Sanctuary library. I spent many days reading papers and copying a lot of info to bring with me after my traineeship. From that time, I was interested in vultures’ juvenile dispersion but never had the opportunity to be involved in a project with this objective.

And again, after almost a decade, a causality joints me one more time to HMS, but this time in Portugal, not in Pennsylvania.

In this new cinereous vulture’s project, HMS is more than a sponsor offering GPS devices. From the beginning of the proposal to HMS, its permanent support and fast reply have encouraged me to work in this project, especially during the hard times of preparations, authorizations, organization, etc. I am sure that the presence of HMS in the project has been a motivation to other bodies to participate and be part of it. The result has been the creation of a task force, where raptor conservation and research organizations such as HMS, a private company such as the Spanish electric company ENDESA, and the government of Portugal, are in a narrow collaboration to study and protect the cinereous vulture in this colony.

Now, with the vultures sending throughout the transmitters lots of daily data, it is time to enjoy learning how these vultures move around the Iberian Peninsula and, who knows, maybe one of them cross the Gibraltar strait toward Africa and offer us new and unexpected information about the movements of this species to sub-Sahara regions!

Check out this video of Alfonso and his team tagging and releasing a cinereous vulture!

Partnership of Promise

By Zoey Greenberg, Science Outreach Coordinator
Hawk Mountain Sanctuary

Physiology: a branch of biology that deals with the functions and activities of life or of living matter (such as organs, tissues, or cells) and of the physical and chemical phenomena involved.
— Merriam-Webster
Hawk Mountain’s American Kestrel Poster displayed on Cedar Crest College lab door.

Hawk Mountain’s American Kestrel Poster displayed on Cedar Crest College lab door.

 On October 23, assistant professor Allison Cornell visited Hawk Mountain from Cedar Crest College to provide a seminar on the physiology of developing American kestrels, emphasizing the role of the Sanctuary’s nest box program in her research. Collaboration between Dr. Cornell and Dr. JF Therrien, senior biologist at Hawk Mountain, began in 2017 and has resulted in exciting science concerning a widely-appreciated falcon species that has been experiencing declines nation-wide.  

 In her seminar, Dr. Cornell highlighted the importance of an integrative approach to understanding the ecological context of a species, stating a cherished quote of hers:

 Behavior is observed physiology.
— Vincent Dethier.
Life History Diagram

Life History Diagram

 As a physiologist, Dr. Cornell’s methods include the assessment of internal as well as external factors that could influence the survival and overall condition of developing birds. Her past work has included assessing the relationships between nestling condition and oxygen storage capacity and identifying how factors such as timing of breeding are related to developmental cues in starling chicks. This type of research adds color to the bigger ecological picture, allowing us to learn more about why birds exhibit the behaviors they do, and how this relates to their overall survival. Factors like pectoral muscle mass, aerobic capacity, red blood cell count, and wing area are just a few telling descriptors that can shed light on what prepares a bird to leave the nest. Turns out, there’s more to it then being kicked out by your parents! 

 For Dr. Cornell, Hawk Mountain’s kestrel nest box program has been instrumental to the success of her research. Nest boxes provide an opportunity to observe kestrel development in a natural setting rather than in a lab where results can be compromised by the lack of true environmental influences. In addition, the nest box program has done the ground work of establishing relationships with landowners, which allows for Dr. Cornell’s research to be conducted in a kestrel-friendly culture.

 Hawk Mountain sees immense value in partnering with an experienced researcher who has the time and passion for conducting good-quality science using Hawk Mountain’s long term data set and putting in the field time to monitor boxes. In addition, trainees and students from both sites are benefiting from the academic opportunities included in this project. Mercy Melo, a student at Cedar Crest, and Jen Houtz, a former conservation science trainee, are both currently involved in the work with Dr. Cornell.

Through the deployment of nest cams and this thorough approach to ecology, Dr. Cornell has given students access to several thought-provoking research topics, including how physiology traits change across nesting period and whether “dead beat” falcon dads have an impact on the physiology of their young. This work has the potential to fill information gaps and provide necessary context to the kestrel decline.

Map from Raptor Population Index showing population status in different regions. Red arrows signify significant declines.

Map from Raptor Population Index showing population status in different regions. Red arrows signify significant declines.

 Collaboration between Hawk Mountain Sanctuary and Cedar Crest College has opened doors to new research, and has also given young professionals the chance to step into raptor ecology with resources that are not always easy to come by: a long term data set, accessible observation sites, and supportive advisors from neighboring institutions. This is a clear win-win for raptor conservation and one that Hawk Mountain is thrilled to be a part of.

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Click here for more information on our kestrel nest box program, or see below for Allison Cornell’s.

Variation in developmental trajectories of physiological and somatic traits in a common songbird approaching fledging. Journal of Experimental Biology. Cornell A, Williams TD. 2017-10-13

Experimentally-increased male social behaviour has no effect on female breeding phenology and performance. Animal Behaviour. Cornell A, Hou JJ, Williams TD. 2017-01-23

Double-brooding and individual quality in a highly synchronous songbird population. The Auk. Cornell A, Williams T. 2016-01-13

Physiological maturity at a critical life-history transition and post-fledging flight ability. Functional Ecology. Cornell A, Gibson KF, Williams TD. 2016-10-04

Mid-winter temperatures, not spring temperatures predict breeding phenology in the European starling Sturnus vulgaris. Royal Society Open Science. Williams TD, Bourgeon S, Cornell A, Ferguson L, Fowler M, Fronstin RB, Love OP

Cape Coral Kestrels

By Kirsten Fuller, Spring 2018 Conservation Science Trainee
Hawk Mountain Sanctuary

Kirsten with a recently banded male American kestrel.

Kirsten with a recently banded male American kestrel.

Over the last year I transitioned from my familiar world of science education and immersed myself in the exciting field of raptor research!  In January, I was lucky to have the opportunity to travel to Cape Coral, Florida to learn about American kestrels with Hawk Mountain research biologist Laurie Goodrich, and long-term kestrel researcher Sue Robertson. 

Sue and her husband Bob first noticed the abundance of American kestrels wintering in Cape Coral in the late 1980’s.  They began trapping and banding the birds, and nearly 30 years later the data is still being collected.

These small falcons prefer open fields with low grass, which makes it easier for them to spot their prey.  In the winter, these birds have plenty of insects to eat in Florida, but they also find small rodents appealing.  This was our bait of choice. We searched for kestrels as we drove around the northern part of the peninsula, which is less developed than the southern part.  When a bird was spotted, we would toss the trap out the door of the car, taking care to do this quickly and stealthily.  It was then a waiting game for the bird to abandon its perch and land on the trap.

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Once we had a bird trapped, we moved quickly to release it and begin the banding process, during which Sue taught me how to measure the length of the tail feathers and the wing chord.  The majority of birds we trapped were male, which was interesting because 30 years ago Sue found that the majority of the small falcons in the same area of Cape Coral were female.  In the past, this may have been attributed to females migrating earlier than males and therefore staking a claim on the available optimal habitat.  A more equal distribution of male and female kestrels in the optimal habitat in Cape Coral, as we observed, may be a reflection of the declining trend in American kestrels that scientists are seeing nationwide.

Over the past 30 years, the available kestrel habitat of Cape Coral has changed quite a bit.  What was once a habitat perfectly maintained for kestrels, with mowed plots of land and plenty of telephone wires for perching (foreshadowing the impending land development), there are now rows of homes and less undisturbed open habitat. 

Sue teaches Kirsten how to measure and band a recently trapped kestrel.

Sue teaches Kirsten how to measure and band a recently trapped kestrel.

It was an invaluable experience to learn from knowledgeable and passionate conservation researchers, Laurie and Sue.  Plus, it wasn’t so bad to hang out in Florida for a few days in January, and I got to catch a glimpse at a Burrowing Owl! I am back at Hawk Mountain now, and I am so thrilled to see American kestrels buzzing around farmlands near the Mountain, preparing for nesting season.  Check out the Hawk Mountain kestrel nestbox cam at www.hawkmountain.org/kestrelcam, and learn more about our farmland raptor conservation efforts at www.hawkmountain.org/farmlandraptors.

A beautiful male American Kestrel, trapped and tagged in Northern Florida. 

A beautiful male American Kestrel, trapped and tagged in Northern Florida. 

A Back-to-Back Snowy Owl Adventure

By Rebecca McCabe,  PhD Student, McGill University
Hawk Mountain Research Assistant

The view on Amherst Island

The view on Amherst Island

It was 6:15 a.m., and the sun had not yet come up as we stepped from our cars onto the ferry deck on the ice-covered waters of Lake Ontario. We were on our way to Amherst Island, a 70 square-kilometer island off the coast of Kingston, Ontario, which is a known hotspot for wintering snowy owls and the reason why we were there.

Myself, Jean-François Therrien (Hawk Mountain), Tom McDonald (Rochester, NY), and Dave Okines (Prince Edward Point Bird Observatory) arrived on the island with the hopes of deploying transmitters on snowy owls as part of the collaborative research of Project SNOWstorm (www.projectsnowstorm.org).

The sun rises over the frozen Lake Ontario.

The sun rises over the frozen Lake Ontario.

As the sun finally rose, we were already driving the main roads searching for white silhouettes in the distance. Luckily for us, Amherst had plenty of snowy owls! We estimated over 25 owls on the island, and now all we had to do was trap a few. We came up short in the morning and afternoon, but as soon as the sun started to set, our luck changed. Within 20 minutes both Dave and Tom had trapped an owl.

Snowy owl Stella, a female trapped and tagged by Project SNOWstorm in Amherst

Snowy owl Stella, a female trapped and tagged by Project SNOWstorm in Amherst

We were fortunate to have a wonderful host, Janet, who allowed us to bring the owls back to her place so we could process them out of the cold. The two immature females, later named Emerald and Stella, were in good condition and each weighed over 2 kg making them eligible to receive a transmitter before being released back into the night.

In just a short amount of time we have learned that the neighboring birds  established territories approximately 3 km from one another on the island, and Emerald has spent more time inland whereas Stella has been going offshore onto the ice during the day. I look forward to following these two individuals as they make their way north in the upcoming months.

One week and 2,370+ km later, I am scanning for snowy owls from the passenger seat again, but this time I am looking out on the prairies of Saskatoon, Saskatchewan. My co-supervisor Karen Wiebe (University of Saskatchewan) and I follow behind raptor bander Marten Stoffel in our pickup truck as we search the tops of telephone poles and fence posts. We spent six hours that day driving the survey route and had easily seen over 30 snowy owls. We were also very fortunate to trap and band six, a record day of trapping snowy owls on the prairies for Marten!

Male snowy owl trapped and tagged in Saskatchewan. 

Male snowy owl trapped and tagged in Saskatchewan. 

The next day we decided to go out again to see if luck was still on our side, this time driving about 150 km northeast of where we were the day before. I was shocked at the stark difference between locations and by the lack of owls we encountered on our second day. The habitat appeared similar but we only saw one adult male that afternoon. Marten decided to try trapping it, even though it was a more difficult catch with blustery winds and the male sitting high atop a transmission tower. Moments before calling it quits, I watched intently (and completely mesmerized) as the owl leapt from its perch and with a few strong flaps, came streaming in towards the bal-chatri before getting trapped.

Spending just a few days on Amherst Island and in Saskatoon and getting to see where these owls spend their winter was not only exciting but informative. I was able to observe them on their territories, take note of their favorite perches, and see first-hand the conditions they were in. As I move forward with my PhD at McGill University and analyze the movements of our GPS tagged snowy owls, my time spent in the field has allowed me to gain a better understanding of how these magnificent birds move throughout the landscape, the habitats they occupy, and the threats they face.

Becca with a recently trapped and tagged snowy owl right before release.

Becca with a recently trapped and tagged snowy owl right before release.

To learn more about these efforts or to support the project, visit hawkmountain.org/snowyowls.