The effects of local weather patterns on malnutrition and death rates of Barred Owls in Vermont (2020-US-45MP-601)
Mike Anderson, SAS Institute, SAS Institute
Anna Morris, Lead Environmental Educator, Vermont Institute of Natural Science
Bren Lundborg, Wildlife Keeper, Vermont Institute of Natural Science
Since 1994, the Vermont Institute of Natural Science’s (VINS) Center for Wild Bird Rehabilitation (CWBR), has been working to rehabilitate native wild birds in the northeastern United States. One of the most common raptor patients CWBR treats is the Barred Owl. Barred Owls are fairly ubiquitous east of the Rocky Mountains. Their call is the familiar “Who cooks for you, who cooks for you all.” They have adapted swiftly to living alongside people and, because of this, are commonly presented to CWBR for treatment. As part of a collaboration with SAS, technical staff from JMP and VINS have been analyzing the admission records from the rehabilitation center. Recently we have used a combination of Functional Data Analysis, Bootstrap Forest Modeling, and other techniques to explore how climate and weather patterns can affect the number of Barred Owls that arrive at VINS for treatment — specifically for malnutrition and related ailments. We found that a combination of temperature and precipitation patterns results in an increase in undernourished Barred Owls being presented for treatment. This session will discuss our findings, how we developed them, and potential implications in the broader context of climate change in the Northeastern United States.
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Speaker | Transcript |
| Mike Anderson | Welcome, everyone, and thank you for joining us. My name is Anna Morris and I'm the lead environmental Educator at the Vermont Institute of Natural Science or VINS in Quechee, Vermont. |
| I'm Bren Lundborg, wildlife keeper at VINS center for wildlife rehabilitation and I'm Mike Anderson JMP systems engineer at SAS. | |
| We're excited to present to you today our work on the effects of local weather patterns on the malnutrition and death rates of wild barred owls in Vermont. | |
| This study represents 18 years of data collected on wild owls presented for care at one avian rehabilitation clinics and unique collaboration between our organization and the volunteer efforts of Mike Anderson at JMP. | |
| Let's first get to know our study species, the barred owl, with the help of a non releasable rehabilitative bird serving as an education ambassador at the VINS nature center. | |
| Yep, this owl was presented for rehabilitation in Troy, New Hampshire in 2013 and suffered eye damage from a car collision from which she was unable to recover. | |
| Barred owls like this one are year-round residents of the mixed deciduous forests of New England, subsisting on a diet that includes mammals, birds, reptiles, amphibians, fish and a variety of terrestrial and aquatic invertebrates. | |
| However, the prey they consume differs seasonally, with small mammals composing a larger portion of the diet in the winter. | |
| Their hunting styles differ in winter as well, due to the presence of snowpack, which can shelter small mammals from predation. | |
| Barred owls are known to use the behavior of snow punching or pouncing downward through layers of snow to catch prey detected auditorially. Here's a short video demonstrating this snow punching behavior. | |
| I've seen in that quick clip barred owls can be quite tolerant of human altered landscapes, with nearly one quarter of barred owl nests utilizing human structures. | |
| There are also the most frequently observed owl species by members of the public in Vermont, according to the citizen science project, iNaturalist, with 468 research grade observations of wild owls logged. | |
| As such, barred owls are commonly presented to wildlife rehabilitation clinics by people who discover injured animals. | |
| The Vermont Institute of Natural Sciences Center for wild bird rehabilitation or CWBR is the federal and state licensed wildlife rehabilitation facility located in Quechee, Vermont. | |
| All wild living avian species that are legal to rehabilitate in the state are submitted as patients to CWBR and we received an average of 405 patients yearly from 2001 to 2019, | |
| representing 193 bird species. 90% of patients presented at CWBR come from within 86 kilometers of the facility. | |
| Of the patients admitted during the 18 year period of the study, 11% were owls of the order Strix varia, comprising six species, with barred owls being the most common. | |
| However, year to year, the number of barred owls received as patients by CWBR has varied widely compared to another commonly received species, the American Robin. | |
| Certain years, such as the winter of 2018 to 2019 had been anecdotally considered big barred owl years by CWBR staff and other rehabilitation centers in the Northeastern US for the large number presented as patients. | |
| One explanation proposed by local naturalists attributes the big year phenomenon to shifts in weather patterns. | |
| When freeze/thaw cycles occur over short time scales, these milder, wetter winters are thought to pose challenges to barred owls relying on snow plunging for prey capture. | |
| Specifically the formation of a layer of ice on top of the snow can prevent owls from capturing prey using this | |
| snow plunging technique as the owls may not be able to penetrate this ice layer. In order to feed...I lost my place. | |
| In order to feed the animals may therefore use alternative hunting locations or styles or suffer from weakness due to malnutrition, which could lead to adverse interactions with humans, resulting in injury. | |
| This study was undertaken to determine if a relationship exists between higher than average winter precipitation and the number of barred owls presented during those years at CWBR for rehabilitation. | |
| Though there are several possible explanations for the variation in the number of patients associated with regional weather, | |
| we sought to determine if there was support for the ice layer hypothesis by further investigating whether barred owls presented during wetter winters | |
| exhibited malnutrition as part of the intake diagnosis in greater proportion than in dryer winters. | |
| This would suggest that obtaining food was a primary difficulty, leading to the need for rehabilitation, rather than a general population increase, which would likely lead to a proportional increase in all intake categories. | |
| Initially we expected that there would be a fairly simple time series analysis relationship to this. | |
| We went and looked at the original data for the admissions and just to compare as, as Bren said, just to compare the data between | |
| the barred owls and the American robins, you can see for bad years, | |
| which I've marked here in blue, except for the the gray one which is actually had a hurricane involved, | |
| we can see there's a very strong periodic signal associated with the robins. We can see that the year-round resident barred owls should have something resembling a fairly steady intake rate, but we see some significant changes in that year to year. | |
| Looking at the contingency analysis, we can see that the green bands, the starvation, | |
| correlates fairly nicely with those years where we have big barred owl years. Again, pointing out 2008, 2015, 2019, | |
| these being ski season years instead, which I'll make clear in a moment. 2017 doesn't show up, but it does have a big band of unknown trauma and cause, and that was from a difference in how they were triaging the incoming animals that year. | |
| The one, the one trick to working with this is that we needed to use functional data analysis to be able to take the | |
| year over year trends and turn them into a signal that we can analyze effectively against weather patterns and other data that we were able to find. | |
| Looking here, it's fairly easy to see that those years that we would call bad years have a very distinctive dogear...dogear...dogleg type pattern. You can see 2008, 2017, 2019, 2015. | |
| Again, | |
| Most importantly, those signals tend to correlate most strongly with this first Eigen function in our principal component analysis. | |
| You can see quite clearly here that component one does a great job with discriminating between the good years and the bad years with that odd hurricane year right in the middle where it should be. | |
| You can also look at the profiler for FPC one and you can see that as we raise and lower that profiler, we see that dogleg pattern become more pronounced. | |
| The next question is, is how do we get the data for that kind of an analysis? How do we get the weather data that we think is important? Well, it turns out that there's a great organization | |
| that's a ski resort about 20 miles away from here that has been collecting data from as far back as the 50s. | |
| And they've also been working with naturalists and conservation efforts, providing their ecological or their environmental data | |
| to researchers for different projects, and they gave us access to their database. | |
| This is an example of base mountain temperature at Killington, Vermont, and you can see that the the bad years, again colored in blue here, | |
| tend to have a flatter belly in their low temperature. You can see for instance, looking at 2007, the first one in the upper left corner, | |
| you can see that there's a steep drop down, followed by a steep incline back up. Whereas 2008, which is one of the bad years for for owl admissions, | |
| we have a fairly flat, and if not maybe in a slightly inverted peak in the middle. And that's fairly consistent, with the exception of maybe 2015, | |
| throughout the other throughout the other the other years. | |
| So I took all of that data and | |
| used functional data explorer to get the principal components for our responses. We end up having, therefore, a functional component on the response and a functional component on the factors. | |
| This is an example of one of those for the...what turns out to be one of the driving factors of this analysis, and you can see it does a very nice job of | |
| pulling out the principal components. The one we're going to be interested in in a moment is this Eigenfunction4. It doesn't look like much right now, but it turns out to be quite important. | |
| So let's put all this together. | |
| I use the combination of generalized regression, along with the autovalidation strategy that was pioneered by Gotwalt and Ramsay a few years ago to | |
| build a model of this of the behavior. We can see we get a fairly good | |
| actual by predictive plot for that. We get a nice r square around 99% and looking at the reduced model, we see that we have four primary drivers, the cumulative rain that shows up. That makes sense. We can't have rain without...we can't have ice without rain. | |
| Also a temperature factor, we need temperature to have a strong...to have ice. But also we have the sum of the daily snowfall or the daily snowfall. That's a max total snowfall per year, and the sum of the daily...the daily rainfall as well. | |
| And taking all of this, we can put together start to put together a picture of what bad barred owl years look like from a data driven standpoint. | |
| We can see fairly clearly. I'm going to show you first again what a bad barred...what a bad year looks like from the standpoint of the | |
| of the of the the admission rates. And we can see here. Let me show you what a bad, bad year looks like. That's a bad year; that's a good year, fairly dramatic difference. Now we're going to have to pay fairly close attention to the... | |
| We're gonna have to pay fairly close attention to the other factors to see because it's a very subtle change in the | |
| the temperatures, in the rain falls that trigger this good year/bad year. It's it's kind of interesting how how tiny the effects are. So first, this is the total snowfall per year. And we're going to pay attention to the slope of this curve | |
| for a good year | |
| and then for a bad year. Fairly tiny change, year over year. | |
| So it's a it's a subtle change, but that subtle change is one of the big drivers. We need to have a certain amount of snowfall present in order to facilitate the snow diving. | |
| The other thing, if we look at rain, we're going to look at the belly of this rainfall right here, around, around week 13 in the in the ski season. | |
| There's a good year. And there's a bad year. Slightly more rain earlier in the year, and with a flatter profile going into spring. | |
| And again, looking at the cumulative rain over the season, a good year tends to be a little bit drier than a bad year. | |
| And lastly, most importantly, the temperature. This one is actually fairly...this is that | |
| belly effect that we were seeing before. We see in early years or in good years that we have that strong decline down and strong climb out in the temperature, but for bad years we get just slightly more bowlshaped effect overall. | |
| And I'm going to turn it over to Bren to talk about what that means in terms of barred owl malnutrition. | |
| Malnutrition has a significant negative impact upon survival of both free ranging owls and those receiving treatment at a rehabilitation facility. | |
| Detrimental effects include reduced hunting success, lessened ability to compete with other animals or predator species for food, and reduced immunocompetence. | |
| Some emaciated birds are found too weak to fly and are at high risk for complications such as refeeding syndrome during care. | |
| For birds in care, the stress of captivity, as well as healing from injuries such as fractures and traumatic brain injuries can double the caloric needs of the patient, thus putting further metabolic stress on an already malnourished bird. | |
| Additionally, scarcity or unavailability of food may push owls closer to human populated areas, leading to increased risk for human related causes of mortality. | |
| Vehicle strikes are the most common cause of intakes for barred owls in all years and hunting near roads and human occupied habitats increases that risk. | |
| In the winter of 2018 to 2019, reports of barred owls hunting at bird feeders and stalking domestic animals, such as poultry, were common. | |
| Hunting at bird feeders potentially increases exposure to pathogens, as they are common sites of disease transmission, it may lead to higher rates of infectious diseases such as salmonellosis and trichomoniasis. | |
| Difficult winters also provide extra challenges for first year barred owls. | |
| Clutching barred owls are highly dependent on their parents and will remain with them long after being able to fly and hunt. | |
| And once parental support ends, they are still relatively inexperienced hunters facing less prey availability and harsher conditions in their first winter. | |
| Additionally, the lack of established territories may lead them to be more likely to hunt near humans, predisposing them to risks such as vehicle collision related injuries. | |
| Previous research on a close relative of the barred owl, the northern spotted owl of the Pacific Northwest, shows a decline in northern spotted owl in fecundity and survival associated with cold, wet weather in winter and early spring. | |
| In Vermont, the National Oceanic and Atmospheric Administration has projected an increase in winter precipitation of up to 15% by the middle of the 21st century, | |
| which may have specific impacts on populations of barred owls and their prey sources. | |
| The findings of this study provide important implications for the management of barred owl populations and those of related species in the wake of a change in climate. | |
| Predicted changes to regional weather patterns in Vermont and New England forecast that cases of malnourished barred owls will only increase in frequency over the next 20 to 30 years as we continue to see unusually wet winters. | |
| Barred owls, currently listed by the International Union for Conservation of Nature as a species of least concern with a population trend that is increasing, will likely not find themselves threatened with extinction rapidly. | |
| However, ignoring this clear threat to local populations may cascade through the species at large and exacerbate the effects of other conservation concerns, such as accidental poisoning and nest site loss. | |
| These findings also highlight the need for protocols to be established on the part of wildlife rehabilitators and veterinarians | |
| for the treatment of severe malnourishment in barred owls, such as to avoid refeeding syndrome, and provide the right balance of nutrients for recovery from an often lethal condition. | |
| Rehabilitation clinics would benefit from a pooling of knowledge and resources to combat this growing issue. | |
| Finally, this study shows yet another way in which climate change is currently affecting the health of wildlife species around us. | |
| Individual and community efforts to reduce human impacts on the climate will not be sufficient to reduce greenhouse gas emissions at the scale necessary to halt or reverse the damage that has been done. | |
| Action on the part of governments and large corporations must be taken, and individuals and communities have the responsibility to continue to demand that action. | |
| We would like to thank the staff and volunteers at the Vermont Institute of Natural Science, as well as at JMP, | |
| who helped collect and analyze the data presented here, especially Gray O'Tool. We'd also like to thank the Killington Ski Resort for providing us with the detailed weather data. Thank you. |
