Written by Rob Miller
My fifth year as part of the Intermountain Bird Observatory (IBO) leading the research on Northern Goshawks within the Sawtooth National Forest has come to a close. By all measures it was a very successful year, but unfortunately my time trouncing through the woods has finished for this season.
Two goshawk nestlings in a newly discovered nest in Piñon Pine, an uncommon nesting substrate.
I thought it might be helpful to dive a bit deeper into the objectives of this program. As with many programs, our efforts are balanced among a number of objectives. Some of our objectives are mostly nested within the other objectives, so we can be efficient in addressing multiple objectives with the same effort.
Core objectives for the Northern Goshawk research and monitoring efforts:
- Evaluate the population trend for this species within the Minidoka Ranger District of the Sawtooth National Forest.
- Evaluate the genetic health of this species within the northern Great Basin region of the western United States, which encompasses the Minidoka Ranger District of the Sawtooth National Forest.
- Evaluate threats to this species, with an emphasis on blood parasites, within the northern Great Basin of the western United States.
- Provide educational and training opportunities for undergraduate students preparing for a career in wildlife biology.
Here’s more detail on each of these objectives.
Objective 1. Evaluate the population trend for this species within the Minidoka Ranger District of the Sawtooth National Forest.
The USDA Forest Service has a set of guidelines requiring each forest to identify Management Indicator Species (MIS) that align with their forest structural objectives. The basic concept is that instead of monitoring all species within the forest, which is not generally feasible, each forest should monitor a few key species whose population status is generally dependent and aligned with the type of forest structure they desire. There are generally a wide range of criteria for choosing good management indicator species (Caro and Girling 2010). Seddon and Leech (2008) suggested a focus on seven criteria for choosing appropriate species: they should have a well-known biology; large home range size; high probability of population persistence; co-occurrence of species of conservation interest; management needs that are beneficial to co-occurring species; sensitivity to human disturbance; and ease of monitoring. The Northern Goshawk meets most of these criteria, at least to some degree. While this approach has its critics, Sergio et al. (2006) has demonstrated a high correlation between Northern Goshawk presence and species diversity including the number of avian species (richness), the number of vulnerable avian species, the number of tree species, and overall avian species diversity (richness and evenness). It is not surprising that many forests, including most in Idaho, have chosen the Northern Goshawk as one of their Management Indicator Species.
Nestlings ready to fledge in the City of Rocks National Reserve.
36 – 38 days old (usually fledge 34-42 days old).
The Sawtooth National Forest is one forest that has specified the Northern Goshawk as an MIS species. They partner with the Intermountain Bird Observatory to accomplish their monitoring objectives as we deliver core biological science to the key questions within the forest. The work within the Sawtooth National Forest has been implemented in steps. IBO worked with the Sawtooth National Forest on goshawks in the late 1990 and early 2000’s. This work was renewed in 2011. My first two years, my thesis years (2011 and 2012), were focused on how the the goshawks utilize the local forest from both a forest structural perspective (Miller et al. 2013) and a prey perspective (Miller et al. 2014). These results had both scientific and management implications. The goshawks within the Minidoka Ranger District of the Sawtooth National Forest have had to adapt to the highly fragmented, island-like structure of the forest, and the absence of the primary food source they consume in most other regions of the world where they exist – tree squirrels.
They don’t all make it. ~20-day old nestling. I discovered this failed nest on the day it failed. Apparently predated by an aerial predator, likely an owl. The nest was covered in feathers.
South Hills, Idaho.
The next two years of the study have included utilizing the habitat models that I established with my thesis work and a lot of effort on the ground to locate previously unknown nesting territories. This activity has been very fruitful in doubling the number of known goshawk territories within the forest while also further refining our understanding of the habitat use.
While we have not located all of the nesting territories within the forest, we now have sufficient coverage to shift our primary attention toward population size, structure, and dynamics. Historical data within the northern Great Basin suggests that female turnover is much higher in the region than elsewhere (Bechard et al. 2006). It has been suggested that turnover rate may be a much more important measure of population health than population size as sink populations, those with a much higher immigration rate than emigration rate, can show stable population size even as the local population heads toward collapse. Turnover refers to the replacement of a breeding adult from one year to the next within a territory. Turnover can occur as the result of death or abandonment (one adult disperses to a new mate and territory). Turnover is primarily measured by mark-resight studies involving trapping and banding the adult birds with color bands which can be read from a distance without having to recapture the bird. In 2014 and 2015, we have deployed many color bands on adult birds in the area and our efforts have already been paying off.
Female Purple Z3 nesting for at least her second year in the Albion Mountains, Idaho. Purple color band Z3 clearly visible on her right leg (photo from 2014, but observed again in 2015). Originally banded as a nestling in the South Hills in 2012. With this single band we have established a natal dispersal distance for this individual and have identified that she has bred for two years in a row in the same territory, all without recapturing her.
These banding activities will enable us to monitor occupancy, productivity, turnover rates, and responses to management actions. Our preliminary results from 2015 suggest that the high turnover observed a decade ago is still occurring at similar rates.
I have two leading hypotheses regarding why the turnover rate may be higher within this forest as compared with other nearby forests.
- My post-fledging mortality hypothesis (leading hypothesis)
- Nest productivity is good by both common measures (young fledged per occupied nest and young fledged per successful nest). (CONFIRMED)
- The breeding season diet within the area is predominantly ground squirrels. (CONFIRMED – Miller et al. 2014)
- Ground squirrels estivate mid-summer removing them from the available food supply for goshawks. (CONFIRMED)
- Female goshawks generally abandon territory the year after a brood failure at a rate of 50% (CONFIRMED).
- There is insufficient food to support the cohort of fledglings after ground squirrel estivation causing high fledgling mortality resulting in complete failure of some broods (NOT confirmed)
- Females abandon the territories in our study area due to these late season failures (NOT confirmed).
- My disease hypothesis
- Black flies within the family Simuliidae are pervasive in the area and carry/pass the Leucocytozoon blood parasite (CONFIRMED – Twin Falls County Pest Abatement District 2012)
- Blood parasites are pervasive within the study area (CONFIRMED – Jeffries et al. 2015)
- Females are more at risk than males due to the amount of time they spend immobile at the nest (Partially Confirmed).
- Female survival is lower as a result of the parasite and the onslaught of black flies (blood loss; NOT confirmed).
We will be working through these research questions in the coming years, assuming we can get funding for the work.
Objective 2. Evaluate the genetic health of this species within the northern Great Basin region of the western United States, which encompasses the Minidoka Ranger District of the Sawtooth National Forest.
The northern Great Basin provides unique habitat for a wide variety of species. The area is home to unique genetic composition for a number of species – a sub-species of Red Crossbill, known as the South Hills Crossbill, that is endemic to the area; an endangered plant called Christ’s Paintbrush that is endemic to the area; a unique form of Lodgepole Pine tree; and a number of bird species that exist nowhere else in Idaho.
Bayard de Volo et al. (2013) investigated the inter-relationship of various North American goshawk populations. Among other things, they found that there were unique mitochondrial haplotypes located in the Rocky Mountains which appear not to have travelled back to the coastal mountain populations. Think of a haplotype as a genetic signature. Bayard de Volo and team believe that as the glaciers retreated in North America, the Rocky Mountains were populated with goshawks from the historical refuges within the coastal mountains and from Arizona. The birds developed new haplotypes in the Northern Rockies, but these haplotypes have not migrated back. Bayard de Volo and team did not investigate the northern Great Basin populations. That is where we at IBO come in.
Rob (me) climbing tree to access the nestlings for banding and genetic sampling.
Team Goshawk intern Kenny and forest biologist Scott banding and sampling the first goshawk nestling of the season. Sublett Mountains, Idaho.
The forest structure and prey composition within the northern Great Basin presents unique challenges for goshawks (Miller et al. 2013, 2014). It is conceivable that the goshawk populations in these areas have undergone evolutionary changes which enable them to better adapt to these environmental options. Therefore, we postulate that we may find unique genetic haplotypes in the area which have not migrated to the core of the Rocky Mountains or back to the coastal populations. Furthermore, if connectivity does exist to these larger contiguous populations to the east and west, to which are the northern Great Basin birds integrated?
A separate analysis process (microsatellites) allows us to look for signs of inbreeding depression. This process is a bit more complicated and takes more time. The mitochondrial haplotype process described earlier looks further back (i.e., thousands of year), whereas the microsatellite process allows us to look more into the past 100 years – post-modern human settlement.
We collect genetic samples by taking blood, removing a feather from a bird, or even collecting a molted feather from the ground beneath the nest. The adult female often molts feathers while incubating eggs on the nest. Some of these molted feathers contain sufficient DNA for extraction. We prefer the least intrusive method (molted feather from ground), but if we need blood for the parasite study (discussed below), then we use it for the DNA as well as blood provides the highest quality sample.
For two years now I have had National Science Foundation funded undergraduate students, Steph in 2014 and Kenny in 2015, working on the genetic analysis. Each have worked with me in the field for a period of four weeks surveying for birds and collecting samples before reporting into the laboratory for the delicate work of genetic analysis.
We are still processing samples, but so far we have not discovered any unique haplotype signatures for the northern Great Basin. This is both good news and bad. Good as that decreases the chance of genetic bottlenecks in the population, bad because it would be really cool to discover that goshawks have evolved specifically to this dry forest island environment. Additionally, our early results indicate that at least the Minidoka Ranger District of the Sawtooth National Forest is well integrated with the Rocky Mountains to the east. We have processed fewer samples using the deeper analysis, but so far we have discovered no signs of inbreeding depress. That is great news from a conservation perspective.
We have collected samples from the Owyhee Mountains in southwestern Idaho (still in analysis) and are partnering with forest biologists across Idaho and in Oregon to expand the geographic scope of our work.
Objective 3. Evaluate threats to this species, with an emphasis on blood parasites, within the northern Great Basin of the western United States.
When I began my work with the goshawks back in 2011, I was informed that most of the birds in the Minidoka Ranger District of the Sawtooth National Forest probably die of a blood parasite that was believed to be in the area. This occurred after I had already designed my thesis work focusing on prey and habitat or I probably would have just focused on the parasite. Regardless, I was able to recruit a volunteer undergraduate student, Michelle, to work on collecting and analyzing blood samples searching for a blood parasite related to Malaria known as Leucocytozoon.
The vector for the disease are flies of the family Simuliidae. These flies are pervasive in the area and pose a double threat. The first threat is from blood loss. At first I didn’t believe that a small fly could have such an impact, but even livestock are at risk of blood loss with these flies. The flies are relentless, targeting the neck and eyes of the nestlings and adult females. I have even donated my blood to one or two of them! The second threat of course is the blood parasite disease.
Goshawk nestlings covered in flies from the family Simuliidae, sucking blood and known vectors of the blood parasite Leucocytozoon. South Hills, Idaho, 2011.
Skin lesions around the neck of an adult female goshawk, likely caused by Black Flies. South Hills, Idaho, 2012.
The adult male birds we handle rarely show the effects of the Black Flies. We believe that these birds have the parasite (confirmed in some), but they are more mobile during the breeding season, better able to avoid the flies. In goshawks the female performs 100% of the incubation and brooding, putting her at constant risk at the nest.
Adult male goshawk with little sign of Black Fly lesions.
Leucocytozoon blood parasite (center) amongst goshawk red blood cells from a sample of blood from a South Hills nestling goshawk taken in 2012. Note: avian blood cells are nucleated, unlike mammalian blood cells.
Our results from 2012 have shown that 28 nestlings from 12 separate nests were all infected with the Leucocytozoon blood parasite. Since samples were taken at a nestling age of approximately 24-28 days old, and the disease takes two weeks to show up in the blood, they were all infected within the first 10 days of their life. This speaks to the pervasiveness of the disease. It is believed that the flies do not themselves have the disease intrinsically, but pick it up as the bite the adult female in the nest and then pass it along as they bite the nestlings. This is referred to as vertical transmission within the nest.
Michelle has submitted a research manuscript for publication in the Journal of Raptor Research, which is due out in the September issue! Woo Hoo!
Jeffries, M. I., R. A. Miller, M. D. Laskowski, and J. D. Carlisle. 2015. High prevalence of Leucocytozoon parasites in nestling Northern Goshawks (Accipiter gentilis) in the northern Great Basin USA. Journal of Raptor Research 49 (3): In Press.
Our next steps are to use genetic techniques to analyze the blood samples for other blood parasites such as avian malaria and Hemaproteus. These diseases are transmitted by mosquitos so we expect less pervasiveness as there are fewer mosquitos in the area. We are working to acquire funding and organize this effort at this time.
4. Provide educational and training opportunities for undergraduate students preparing for a career in wildlife biology.
In my five years of work on goshawks, I have directly employed six undergraduate students on these projects. Four are working as wildlife biologists or in related fields (Lauren, Emmy, Mike, and Steph), one is in graduate school leading her own research (Michelle), and one is still an undergraduate (Kenny). I hope that I have provided an excellent opportunity for them to learn and grow and have provided sufficient guidance to help them be more successful in their careers. Michelle’s publication due out next month is a tremendous accomplishment. I feel more honored to have mentored her in the process than to have my own publication. I expect this to be the first in a number of mentored publications in which I get to participate (I am still working on my own as well).
In addition to the direct engagement of students on the project, for the last two years I have hosted a two day goshawk workshop for the group of undergraduate raptor research students participating in the National Science Foundation funded Research Experience for Undergraduates (REU) program at Boise State University. This program hires eight or nine undergraduates each year from across the country. It is highly competitive with over 250 applicants each year. I have hosted one student each of the past two years – Steph in 2014 and Kenny in 2015, focusing on genetics. However, for one weekend each year, we bring all eight or nine students to the study area to focus on goshawks. For most students this is the first time they have seen a goshawk in the wild. They are trained on identification, surveying, tree climbing, genetic sampling, etc. What a great opportunity!
It is hard to boil down five years of work into a single blog post! Hopefully you found it worthwhile.
An old friend. Banded adult female goshawk nesting where I would expect her – Band: Purple N4.
Literature Cited:
Bayard De Volo, Shelley, Richard T. Reynolds, Sarah A. Sonsthagen, Sandra L. Talbot, and Michael F. Antolin. 2013. “Phylogeography, Postglacial Gene Flow, and Population History of North American Northern Goshawks (Accipiter Gentilis).” The Auk 130 (2): 342–354.
Bechard, M. J., G. D. Fairhurst, and G. S. Kaltenecker. 2006. “Occupancy, Productivity, Turnover and Dispersal of Northern Goshawks in Portions of the Northeastern Great Basin.” Studies in Avian Biology 31: 100–108.
Caro, Timothy M, and Sheila Girling. 2010. Conservation by Proxy Indicator, Umbrella, Keystone, Flagship, and Other Surrogate Species. Washington, D.C.: Island Press.
Jeffries, M. I., R. A. Miller, M. D. Laskowski, and J. D. Carlisle. 2015. High prevalence of Leucocytozoon parasites in nestling Northern Goshawks (Accipiter gentilis) in the northern Great Basin USA. Journal of Raptor Research. In Press.
Miller, R. A., J. D. Carlisle, M. J. Bechard, and D. Santini. 2013. “Predicting Nesting Habitat of Northern Goshawks in Mixed Aspen-Lodgepole Pine Forests in a High-Elevation Shrub-Steppe Dominated Landscape.” Open Journal of Ecology 3 (2): 109–115.
Miller, R. A., J. D. Carlisle, and M. J. Bechard. 2014. “Effects of Prey Abundance on Breeding Season Diet of Northern Goshawks (Accipiter Gentilis) within an Unusual Prey Landscape.” Journal of Raptor Research 48 (1): 1–12.
Seddon, Philip J., and Tara Leech. 2008. “Conservation Short Cut, or Long and Winding Road? A Critique of Umbrella Species Criteria.” Oryx 42 (02): 240–45.
Sergio, F., I. Newton, L. Marchesi, and P. Pedrini. 2006. “Ecologically Justified Charisma: Preservation of Top Predators Delivers Biodiversity Conservation.” Journal of Applied Ecology 43 (6): 1049–1055.
Twin Falls County Pest Abatement District. 2012. Why all the Black Flies. Twin Falls, Idaho. http://www.tfcpad.qwestoffice.net/.
Wiens, J. D., and F. T. Reynolds. 2005. “Is Fledging Success a Reliable Index of Fitness in Northern Goshawks?” Journal of Raptor Research 39 (3): 210–221.