AUTHOR BLOG: Old-growth specialist Helmeted Woodpeckers roost exclusively in decay-formed tree cavities

Martjan Lammertink, Juan Manuel Fernández, and Kristina Cockle

Linked paper: Helmeted Woodpeckers roost in decay-formed cavities in large living trees: A clue to an old-growth forest association by M. Lammertink, J.M. Fernández, and K.L. Cockle, Jr, The Condor: Ornithological Applications 121:1, February 2019.

Woodpeckers make holes in trees. Don’t they?

Many species of woodpeckers depend on mature forest. Usually, it’s because they need large decaying or dead trees for foraging and excavating nest holes. Since they roost overnight in their old nest cavities, we usually don’t think about roost cavities as a separate consideration for conservation management.

The Helmeted Woodpecker (Celeus galeatus) is different. We know this globally vulnerable species is associated with well-preserved, native Atlantic Forest, but why? We radio-tracked Helmeted Woodpeckers in Argentina’s Misiones province to learn more about their foraging, nesting, and ranging ecology, as well as their coexistence with other woodpecker species. We expected their roosting behavior to follow the pattern of other woodpeckers, with roost sites predominantly in excavated cavities.

Not so. We found 21 roost cavities used by at least 15 individual Helmeted Woodpeckers. Incredibly, none of them were excavated. All of the roosts were in cavities formed by natural decay in large, usually living trees. This makes the Helmeted Woodpecker unique.

Helmeted Woodpeckers, it turns out, have a lot of unusual roosting habits. Although other woodpeckers descend into their cavity to roost, Helmeted Woodpeckers go up inside the cavity and cling to the wall above the entrance. After nesting, each parent takes a fledgling to its separate decay-formed roost cavity, where they roost together for up to 67 days. So they don’t just need decay-formed roost cavities, they need decay-formed roost cavities with sufficient interior space above the entrance for two individuals.

Helmeted Woodpeckers can excavate cavities – they do it for nesting. They often forage on small dead branches and bamboo stalks, which are common in disturbed forest patches. But these birds are found primarily in old forests, and the fact that they roost in decay-formed cavities, which occur mainly in large, old trees, may go a long way toward explaining this association.

The cavities that Helmeted Woodpeckers use as roosts are in high demand by other forest animals, too. We found eight other bird species and at least two species of social insects using these cavities. Helmeted Woodpeckers fought to defend their roost cavities and sometimes lost them to White-eyed Parakeets (Psittacara leucophthalmus) and White-throated Woodcreepers (Xiphocolaptes albicollis). We think these roost cavities are a high-quality, limited resource, critical not just for Helmeted Woodpeckers but for a broad suite of forest species.

Helmeted Woodpeckers have already lost over 90% of their former range to deforestation, and nearly all remaining forests in their range have a history of selective logging. Unfortunately, logging operations target the same species and sizes of trees that typically hold Helmeted Woodpeckers roost cavities. To stop the ongoing decline of Helmeted Woodpeckers, the largest living trees should be retained in logging concessions, and more forested areas should be spared permanently from timber production so that they can return to old-growth conditions.


Sharing of a roost site in a decay-formed cavity by an adult male and juvenile Helmeted Woodpecker. This is a still from a video archived in Macaulay Library. Photo credit: Martjan Lammertink

AUTHOR BLOG: How Google Images can help us understand Martial Eagles’ diet and decline

Vincent Naude

Linked paper: Using web-sourced photography to explore the diet of a declining African raptor, the Martial Eagle (Polemaetus bellicosus) by V.N. Naude, L.K. Smyth, E.A. Weideman, B.A. Krochuk, and A. Amar, The Condor: Ornithological Applications 121:1, February 2019.

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A Martial Eagle prepares to eat a monitor lizard. Photo by Riaan Marais.

The Martial Eagle is one of the largest and most powerful of the booted eagles. These menacing giants dominate the skies over sub-Saharan Africa, ranging from Senegal to Somalia and down to South Africa. Their name is derived from the Latin word Martialis, meaning “from Mars,” referring to the Roman god of war—quite fitting, as these raptors are expert hunters, whether swooping in on their quarry from breathtaking heights or sitting secretly perched in the dense foliage of a tree ready to ambush. Unfortunately, a recent, rapid decline across much of their range has led to their uplisting from “Near Threatened” to “Vulnerable” on the IUCN Red List of Threatened Species. While it is still unclear what factors are driving this decline, evidence suggests that it may be related to their diet, specifically a reduction or shift in the availability of prey species. So, what do Martial Eagles eat, how do we measure that, and what can we do with this information?

Very little data is available on the diet of Martial Eagles. Regrettably, only three published studies exist to date, and these were conducted in South Africa in the 1980s. Traditionally, raptor diet is measured by examining prey remains or pellets at nest sites, as well as through hide watches, camera traps, and even stable isotopes. However, large eagle nests are surprisingly hard to find, and these approaches only measure diet in the breeding season. Eagles have enormous home ranges (>100km2) and nest at low densities (1 pair per 140km2), which makes studying them costly and logistically challenging.

To overcome some of these challenges, we turned to a form of citizen science: using Google Images to determine Martial Eagle diet across their range from uploaded photographs. Using a specialized, open-access software platform called MORPHIC to scan Google Image results for a series of twelve unique search terms, we found 4872 photographs, 254 of which turned out to be of Martial Eagles and their prey after checking for duplication and filtering by relevance. They were taken in eight African countries between 1998 and 2016. From these photographs, we determined relative eagle age based on plumage, recorded the eagle’s feeding position, identified the prey items, and estimated prey weight.

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Martial Eagle diets in different areas of Africa.

We were pleasantly surprised to find that not only did our data agree with the only existing studies in South Africa, but it also agrees with a recently completed master’s thesis on Martial Eagle diet and behavior in the Maasai Mara of Kenya. We were able to expand on the data produced for South Africa and even reliably determine diet for four new countries.

Overall, Martial Eagles everywhere feed on the same combination of bird, mammal, and reptile prey, but the proportions of these prey types differ drastically between eastern and southern Africa. While eagles in both regions consume equal proportions of bird prey, eagles in eastern Africa rely more heavily on mammals, and those in southern Africa eat more reptiles. Martial Eagles in largely arid areas like Namibia, Botswana, and western South Africa consume mostly bird prey, whereas in wetter areas like Tanzania and Kenya, they feed more on mammals. This is obviously dependent on the relative abundance of these prey species, but the overall trends can tell us something about how dietary declines or shifts in prey numbers might be affecting these eagles. Adult eagles also consumed more bird prey than non-adults overall, which makes sense as adults are more experienced and birds are harder to catch.

Bird prey consisted mostly of guineafowl and spurfowl species, with some surprising rarities such as Spur-winged Geese, flamingos, and Kori Bustards. Antelope and small mammal species were the most frequently taken mammals, but eagles were also observed eating lion cubs, caracal, and even chacma baboons. Reptile prey included monitor lizards, a rock python, and even small Nile crocodiles.

While our study doesn’t have the fine-scale power of the nest-site surveys, we have been able accurately replicate these existing studies and provide landscape-level diet data on Martial Eagles at a fraction of the effort and cost. We hope that these new, citizen science-based and open access data approaches find a place in a conservation, as they provide new perspectives to old problems and can sometimes unveil landscape-level trends which had previously been nearly impossible to assess.

AUTHOR BLOG: How do Gunnison Sage-Grouse fare after translocation?

Shawna Zimmerman

Linked paper: Evaluation of genetic change from translocation among Gunnison Sage-Grouse (Centrocercus minimus) populations by S.J. Zimmerman, C.L. Aldridge, A.D. Apa, and S.J. Oyler-McCance, The Condor: Ornithological Applications 121:1, February 2019.

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Researchers collected Gunnison Sage-Grouse feathers for genetic analysis. Photo by Shawna Zimmerman.

Humans moving animals around for conservation?! This may not immediately sound like an action we should advocate for, but the purposeful movement of individuals from one place to another is often an effective way to give small, declining populations a boost in size or increase their genetic diversity. As human alteration of landscapes continues to fragment wildlife habitat and species distribution, this type of action is becoming increasingly common.

Despite their common use, the long-term effects of these purposeful movements, called “translocation,” are difficult to measure. One way to evaluate their impact is through genetic sampling—collecting genetic samples before individuals are moved between locations, and then comparing those data to genetic samples collected after individuals have been released in their new location and given some time to acclimate.

The Gunnison Sage-Grouse (Centrocercus mimimus) is a federally threatened bird species that persists as seven geographically separated populations, which are far enough apart that birds don’t frequently move between them. One population, located in the Gunnison Basin of Colorado, includes approximately 86% of the remaining individuals in the species, maintains a relatively stable population size from year to year, and is the most genetically diverse of all the populations. The six much smaller satellite populations have seen dramatic fluctuations in their population sizes and also have much lower genetic diversity.

Colorado Parks and Wildlife (CPW) were concerned about the viability of the satellite populations because of their small size and low genetic diversity, so in 2005 they began moving birds from the Gunnison Basin to four of the satellite populations. These efforts continued through 2014.  While CPW was able to use radio collars to track some of the translocated individuals for a year, longer-term information on the fate of these individuals was lacking. Specifically, they were uncertain if these birds survived for more than a single year, or if they were integrating into the population and reproducing with the local birds. My co-authors and I set out to answer these two specific unknowns.

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Researcher Shawna Zimmerman walks to a sage-grouse lek site to collect feathers. Photo by Keith Williams.

Genetic sampling can provide insight into both of these questions. Fortunately, we still had samples collected from all of the populations as part of a previous study done prior to translocation efforts, and we used these samples as our reference for change. In another stroke of luck, Gunnison Sage-Grouse have a lek mating system. This means birds gather in approximately the same location each spring to display and choose mates, leaving feathers behind. By visiting the mating sites to pick up these feathers, we could collect genetic samples without needing to disturb the birds. We collected feathers from leks predominantly between 2012 and 2014, and we used these samples to determine the current genetic state of the species.

To find out whether translocated birds were surviving, we first looked at the genetic diversity of each population and how different the individual populations are from each other, detecting some degree of change in all populations that received Gunnison Basin transplants. Looking at changes in genetic diversity at the individual level, we also found that individuals in populations that received Gunnison Basin transplants had increased genetic diversity which originated from Gunnison Basin, suggesting that translocated birds were reproducing.

Our results also showed that levels of genetic change varied among populations, indicating that the impacts of translocation differed from place to place. The two populations with the largest detected increase in genetic diversity also had a corresponding increase in population size, which indicates that translocation efforts may have had a particularly positive impact on these populations.

Our approach to evaluating translocation efforts in Gunnison Sage-Grouse was effective at detecting change that could be attributed to a conservation action, and the non-invasive sampling methods we used could be continued in the future if additional translocation efforts occur. The ability to evaluate the effects of conservation efforts non-invasively is particularly important for a species with federal protection, which makes other sampling approaches less feasible. The positive impact of translocation efforts increases hope for the persistence of the small satellite populations. However, if translocation efforts do not continue or natural dispersal among populations is not increased, observed gains in genetic diversity will ultimately be lost.

AUTHOR BLOG: How vulnerable are California’s Great Gray Owls to wildfire?

Rodney Siegel

Linked paper: Short-term resilience of Great Gray Owls to a megafire in California, USA by R.B. Siegel, S.A. Eyes, M.W. Tingley, J.X. Wu, S.L. Stock, J.R. Medley, R.S. Kalinowski, A. Casas, M. Lima-Baumbach, and A.C. Rich, The Condor: Ornithological Applications 121:1, February 2019.

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A Great Gray Owl nest within an area recently burned by the 2013 Rim Fire in Yosemite National Park. Photo credit: Dustin Garrison

Throughout western North America, the combination of longer, hotter dry seasons and dense forests is yielding more frequent, larger, and more severe wildfires, including immense “megafires.” Habitat loss from increased fire activity could put wildlife species that depend on mature forest at risk. Concern over this threat is an increasingly important driver of forest management efforts in California’s Sierra Nevada, but recent efforts to assess the consequences of megafires on one bird species associated with the region’s mature forest, the California Spotted Owl (Strix occidentalis), have yielded conflicting results. Some research suggests that California Spotted Owls may be vulnerable to habitat loss and local extirpation due to forest fire, while other studies indicate that the owls may be fairly resilient, at least to low- and mixed-severity fire.

Like Spotted Owls, the Great Gray Owl (Strix nebulosa) is imperiled in California (where it is listed by the state as endangered) and is associated with mature forest. California’s Great Gray Owls typically nest in large, dead trees in shady forests adjacent to mountain meadows. In 2013 the Rim Fire, the largest fire on record in the Sierra Nevada, burned 104,000 hectares in Yosemite National Park and Stanislaus National Forest – the heart of Great Gray Owl’s range in California. Within the burned area were 23 meadows known to be occupied by Great Gray Owls during the decade prior to the fire, nearly a quarter of all known or suspected territories in California at the time.

We analyzed 13 years (2004–2016) of Great Gray Owl survey data from 144 meadows in the central Sierra Nevada, including meadows inside and outside the Rim Fire perimeter in Yosemite National Park and Stanislaus National Forest, to assess the effect of the fire on Great Gray Owls’ persistence during the early post-fire years. Would Great Gray Owls continue to use historically occupied meadows within the burned area, or would the fire cause those sites to go vacant?

During three years of surveys after the fire, we detected Great Gray Owls at nearly all (21 of 22) surveyed meadows within the burned area that were occupied during the decade prior to the fire, and anecdotal evidence indicated that the owls were not only present but actually nested at many of these sites during the post-fire years. Analyzing the full dataset, including surveys conducted before and after the fire as well as inside and outside the burned area, revealed that rather than decreasing after the fire, owls’ persistence actually increased at meadows across the study area. This increase suggests that the owls remained resilient during the three years after the Rim Fire and that other factors such as weather were likely favorable to Great Gray Owls during those post-fire years.

Our results indicate that wildfires, including unusually large megafires, may not pose a great threat to Great Gray Owls in the short term. However, processes not apparent during our study’s short timeframe, including the eventual decay and loss of the large snags that the fire created, could affect the owls’ longer-term persistence after fire. Further study is needed to determine whether Great Gray Owls continue to be resilient to fire over longer timeframes.

More information about The Institute for Bird Populations’ Great Gray Owl research and conservation efforts is available at http://birdpop.org/pages/greatGrayOwlResearch.php.

Road Proximity May Boost Songbird Nest Success in Tropics

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A juvenile White-rumped Shama with identifying leg bands. Photo credit: Rongrong Angkaew

In the world’s temperate regions, proximity to roads usually reduces the reproductive success of birds, thanks to predators that gravitate toward habitat edges. However, the factors affecting bird nest success are much less studied in the tropics—so does this pattern hold true? New research published in The Condor: Ornithological Applications shows that interactions between roads, nesting birds, and their predators may unfold differently in Southeast Asia.

Rongrong Angkaew of King Mongkut’s University of Technology Thonburi and her colleagues placed 100 next boxes for the cavity-nesting White-rumped Shama in forest interior and 100 near a road at an environmental research station in northeast Thailand. Monitoring nests and radio-tracking 25 fledglings from each site for seven weeks, they found that nest success was 12% higher and post-fledging survival 24% higher at the edge versus the interior—the opposite of the pattern commonly observed in temperate regions.

“There were some special challenges involved in carrying out the field work,” says Angkaew. “When we started setting up the nest boxes in the field, we found a lot of tracks and other signs of poachers and illegal hunting, so we had to avoid some parts of the forest edge in order to reduce human disturbance to our nest boxes, which could have affected nestling and fledgling survival rates.”

Predators caused 94% of nest failures and 100% of fledgling mortality, and locally important predators of small birds, such as green cat snakes, northern pig-tailed macaques, and raptors, appear to prefer interior forest habitat. Fledglings also preferred to spend time in dense understory habitat, which provides cover from predators and was more available near roads.

Overall, the study’s results suggest that the effects of roads on birds’ reproductive success depend on local predator ecology—the same rules don’t necessarily apply in different biomes. Angkaew and her coauthors hope that more studies like theirs will help identify key nest predators and assess their foraging behaviors in multiple landscapes, in order to determine the best ways to conserve vulnerable bird species in areas affected by human development.

Nesting near road edges improves nest success and post-fledging survival of White-rumped Shamas (Copsychus malabaricus) in northeastern Thailand is available at https://academic.oup.com/condor/article/121/1/duy013/5303795.

About the journal: The Condor: Ornithological Applications is a peer-reviewed, international journal of ornithology, published by the American Ornithological Society. For the past two years, The Condor has had the number one impact factor among 27 ornithology journals.