Improving “Silvopastures” for Bird Conservation

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Black-crowned Antshrikes are among the insectivorous birds that forage less efficiently in silvopasture habitat. Photo credit: B. Tarbox

The adoption of “silvopastures”—incorporating trees into pastureland—can provide habitat for forest bird species and improve connectivity in landscapes fragmented by agriculture. But how do silvopastures measure up to natural forest habitat? New research from The Condor: Ornithological Applications shows that birds in silvopasture forage less efficiently than those in forest fragments but offers suggestions for how silvopasture habitat could be improved.

The University of Florida’s Bryan Tarbox and his colleagues observed the foraging and flocking behavior of insect-eating birds in silvopastures on farms in the Colombian Andes between 2013 and 2015. They found that silvopastures were less structurally complex than forest fragments, with fewer and smaller trees, a sparser understory, and less diversity of tree species. Birds in silvopastures attacked insects less often, were less selective about where they foraged, and were less likely to join mixed-species flocks. Flock members attacked prey more frequently than solitary birds in forest fragments, but not in silvopastures, suggesting that something about silvopasture habitat negated the benefits of joining a flock.

The results show that silvopasture habitat could be improved by managing for higher tree species diversity and greater structural complexity, but that preserving natural forest fragments in agricultural landscapes is also crucial. “I hope people don’t get the impression that our results mean silvopastures aren’t a good idea,” says Tarbox. “The existing literature makes it clear that silvopastures are beneficial for biodiversity conservation. I think the big takeaway here is the importance of getting to the details of how specific land uses impact particular species or functional groups, so that we can figure out the best regional configurations of land use, given the competing needs of wildlife and agriculture.”

“Protected areas alone will be insufficient to conserve biodiversity at global scales. Instead, we must find ways to safeguard species and ecosystems while also sustaining human communities and livelihoods that depend upon local resources,” according to Cornell University’s Amanda Rodewald, an expert on bird responses to human land use who was not involved with the research. “In their study of insectivorous forest birds, Tarbox and his colleagues report that Andean silvopastures provided low quality foraging habitats and, as such, may fail to support resident and migratory birds as well as forest fragments. Fortunately, the study points to several strategies, such as planting preferred tree species and creating specialized microhabitats, that can be implemented at local and regional scales to improve suitability of silvopastoral habitats for birds.”

Foraging ecology and flocking behavior of insectivorous forest birds inform management of Andean silvopastures for conservation is available at http://americanornithologypubs.org/doi/full/10.1650/CONDOR-18-1.1.

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.

Newly Identified African Bird Species Already in Trouble

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A Mountain Sooty Boubou. Photo credit: J. Engel

Central Africa’s Albertine Rift region is a biodiversity hotspot consisting of a system of highlands that spans six countries. Recent studies have shown that the population of sooty bush-shrikes occupying the region’s mid-elevation forests is a distinct species, and new research from The Condor: Ornithological Applications reveals that this newly discovered species may already be endangered due to pressure from agricultural development.

The newly identified mid-elevation species has been dubbed Willard’s Sooty Boubou, as opposed to the previously recognized high-elevation species, the Mountain Sooty Boubou. The Field Museum’s Fabio Berzaghi (now with the CEA Laboratory for Sciences of Climate and Environment in France) and his colleagues used museum records and bird survey records to analyze the ecological niche occupied by each species, and their results confirm that there is very little overlap between the ranges of the two species—Willard’s Sooty Boubou is found at approximately 1200–1900 meters and the Mountain Sooty Boubou at 1800–3800 meters. In Burundi, Rwanda, and Uganda, 70% of the potential for Willard’s Sooty Boubou lies outside of protected areas and has been converted to agriculture, and the numbers for the Democratic Republic of Congo are only slightly better.

Willard’s Sooty Boubou joins several other imperiled bird species that depend on the region’s mid-elevation forests, which have been largely overlooked by conservation efforts. “The Albertine Rift is a crossroads of amazing biodiversity, dramatic and diverse landscapes, and heartbreaking social and political unrest. It goes from glaciers to volcanoes to plateaus to lakes, with a succession of vegetation types from high-elevation cloud forests to lowland tropical forests,” says Berzaghi. “It is home to gorillas and forest elephants as well as a high number of endemic animal and plant species. Unfortunately, much of the region has gone through never-ending conflicts, with very negative consequences for both humans and biodiversity, and conservation involving local populations is paramount.”

“This paper provides additional data in support of the recognition of Willard’s Sooty Boubou as a species distinct from Mountain Sooty Boubou. Clarification of the niche that Willard’s Sooty Boubou occupies, that of mid-elevation forests, distinct from the higher-elevation Mountain Sooty Boubou, is important, because these habitats are among the most heavily impacted in Africa from agriculture,” according to UC Berkeley’s Rauri Bowie, an expert on African birds who was not involved in the study. “Conservation agencies have an opportunity to move beyond taxonomic debate and use the models derived from this species to improve conservation outcomes for not only this species, but also a broad set of mid-elevation Albertine Rift endemic vertebrates through protection of mid-elevation forests that have received relatively little protection in comparison to high-elevation montane habitats.”

Comparative niche modeling of two bush-shrikes (Laniarius) and the conservation of mid-elevation Afromontane forests of the Albertine Rift is available at http://americanornithologypubs.org/doi/full/10.1650/CONDOR-18-28.1.

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.

AUTHOR BLOG: “Bird-in-the-middle”—a mid-elevation tropical species stuck in limbo

Fabio Berzaghi & John Bates

Linked paper: Comparative niche modeling of two bush-shrikes (Laniarius) and the conservation of mid-elevation Afromontane forests of the Albertine Rift by F. Berzaghi, J.E. Engel, A.J. Plumptre, H. Mugabe, D. Kujirakwinja, S. Ayebare, and J.M. Bates, The Condor: Ornithological Applications 120:4, October 2018.

Capture

A search through the tropical forest literature for “mid-elevation forests” reveals relatively few results compared to a search for high-elevation or lowland forests, and looking at a map of protected areas and land cover in mountainous tropical regions makes it clear why. For example, in the African Albertine Rift, most national parks tend to be in high elevation areas where slopes are steep and land conversion for human use is more difficult. As we move down the slopes, the habitat starts degrading until we arrive in the lowlands, where almost no intact habitat remains, particularly on the eastern side of the Rift.

In 2010, Voelker et al. described a new species of bush-strike, the Willard’s Sooty Boubou (Laniarius willardi), and noticed that this species occurs at lower elevations than its sister species, the Mountain Sooty Boubou (Lanarius poensis). We were thus wondering how much habitat was left for this mid-elevation species, knowing that in this region lower-elevation forests are degraded or have been converted to agriculture. Using niche modeling and land cover data, we discovered that these two species of birds reside at different elevations across a small portion of montane Africa, overlapping only in part. Unfortunately, the habitat for L. willardi has been greatly reduced, because mid-elevation forests are outside protected areas and national parks. L. willardi may not be able to move to higher elevations, as its preferred environmental conditions are between 1200 and 1900 meters; a large portion of its suitable habitat is found in the Democratic Republic of the Congo’s Itombwe Plateau, technically a protected area but problematic to protect.

The plight of L. willardi is probably similar to that of many other mid- and low-elevation species in the area. Even though our results are not such good news for birds and other mid-elevation species in the region, we also want to highlight the importance of scientific collaborations with local researchers and conservation units. These collaborations help us define habitats and species in need of attention. Importantly, the authors of our study are a combination of Africans and non-Africans, with a range of research foci including ornithology and conservation but also niche modeling and bioinformatics. The data used in our study are based on both museum specimens (historical and modern) and modern field observations, which were carried out by teams that always included African students and scientists from the countries where the data were collected. Conservation can only be successful in the long run if in-country capacity for conservation science is developed around the world.

The discovery of L. willardi and its description were made possible through modern scientific collection during collaborations between local Albertine Rift ornithologists and the Field Museum. Data from such modern collections will help clarify lingering concerns in the taxonomic community (particularly Birdlife International and the IUCN) in regards to the status of these two species relative to other black boubous occurring far to the west in the Cameroonian Highlands. Work like this has great value, because it allows highlighting issues of conservation concern at both regional and local scales. Each region of the Albertine Rift has its own history and ongoing issues with deforestation, instability and protection. There is no “one size fits all” solution to conservation in the Albertine Rift, but this paper helps emphasize that there is regional expertise in the form of researchers and conservation professionals who will make a difference. Opportunities to work with international colleagues to combine conservation and science, as in this paper, will be instrumental in building efforts to protect the incredible biota of this wonderful region.

Mini Video Cameras Offer Peek at Hard-to-Observe Bird Behavior

 

Fledging behavior—when and why baby birds leave the nest—is something scientists know very little about. Rarely is someone watching a nest at just the right moment to see fledging happen. To get around this, the researchers behind a new study from The Auk: Ornithological Advances deployed miniature video cameras to monitor over 200 grassland bird nests in Alberta, North Dakota, Minnesota, and Wisconsin, and they found that fledglings’ decision-making process is more complex than anyone guessed.

Christine Ribic from the U.S. Geological Survey and her colleagues tested two competing hypotheses about fledglings’ decision making. Birds might leave the nest early in the day to maximize the amount of time they have to find a safe place to hide from predators before nightfall. Alternatively, once their siblings start to leave, the remaining birds might decide to stay in the nest longer to take advantage of reduced competition for the food their parents provide, resulting in spread-out fledging times. Video data analyzed by Ribic and her colleagues showed that the more siblings in a nest, the longer it took for all of them to fledge, consistent with the idea that some young may stay behind to take advantage of reduced competition after the first nestlings leave. Ribic and her co-authors discovered that 20% of nests took more than one day to completely finish fledging. Fledging behavior also varied between species and over the course of the breeding season, for reasons that remain unclear.

As they decide when to fledge, the nestlings of grassland birds are balancing two competing demands. On one hand, staying in the nest longer gives them more time to grow and develop before facing the risky outside world. On the other hand, predation risk might increase with time spent in the nest.

“It was exciting to see events naturally occurring in an area of avian biology where very little is known, and was only possible due to the use of video surveillance systems,” says Ribic. “It seems fledging is more complex than we previously thought. We were surprised by the span of time over which grassland bird species fledge, with some species starting to fledge in the early morning and others closer to noon, and by the frequency of fledgings that spanned multiple days.”

“Considerable research attention has focused on the breeding biology of birds, but until recently some events have been difficult to observe. Luckily, decreases in the size and cost of video equipment have allowed researchers to study these hard-to-observe events, such as the brief moments when a predator causes a nest to fail. This study took things a step further to begin exploring the point in time when young birds fledge from the nest,” adds the University of Illinois’s T.J. Benson, an expert of bird nesting behavior who was not involved in the study. “There are relatively few existing ideas for what influences the timing of nest departure by young birds, and Ribic and her colleagues put forth an interesting idea about the potential role of food availability in influencing fledging. Use of video technology to examine nest predation has become widespread, and this paper provides a great example of the other interesting aspects of breeding biology that can be examined in such studies.”

Diel fledging patterns among grassland passerines: Relative impacts of energetics and predation risk is available at http://www.americanornithologypubs.org/doi/full/10.1642/AUK-17-213.1.

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology published by the American Ornithological Society. The Auk commenced publication in 1884 and in 2009 was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

AUTHOR BLOG: What time do baby birds leave home?

Christine Ribic

Linked paper: Diel fledging patterns among grassland passerines: Relative impacts of energetics and predation risk by C.A. Ribic, C.S. Ng, N. Koper, K. Ellison, P.J. Pietz, and D.J. Rugg, The Condor: Ornithological Applications 120:4, October 2018.

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A Grasshopper Sparrow chick leaves its nest. Credit: C. Ribic, USGS

We know that human kids grow, mature, and gradually move towards a life that is independent of their parents’ home.  The same is true for baby birds: they also have to decide when the time is right to leave the nest and start on their journey to independence. This seems to involve a balancing act between making sure they are big and healthy enough to survive independently, while leaving the nest quickly to avoid predators. Nests are busy places where chicks beg for food and parents are constantly coming and going with food deliveries. All of this activity could easily draw predators to the nest! The timing of chicks leaving the nest (fledging) isn’t well understood, particularly for birds that live in grasslands, many of which are threatened or endangered due to habitat loss.

Our new research focused on a variety of grassland songbirds, such as meadowlarks, sparrows, and longspurs. We found that the time baby birds leave the nest has more to do with having enough food (energetics) than avoiding predators. This is surprising because research on birds nesting in shrubs says that risk of predation is the most important thing affecting when chicks leave the nest. This suggests that nests in grasslands (hidden on the ground with protective cover from surrounding grasses and a few low shrubs) face different risks than nests placed in shrubs.

We found that grassland chicks can start to leave anytime throughout the day and when they leave depends on what species they are. Some chicks, like Clay-colored Sparrow and Grasshopper Sparrow, usually left the nest in the early morning, while Eastern Meadowlark and Chestnut-collared Longspur left closer to mid-morning. But sometimes chicks delayed leaving until the afternoon, with their siblings waiting until the next day to depart. The time it takes for all the chicks to leave a nest can be several hours to more than a day! Maybe some chicks are taking advantage of their siblings’ early departures to get more food and attention from mom and dad before they finally leave, too.

Measuring fledging time can be tricky because chicks run in and out of the nest multiple times before leaving for good. We don’t know why they do this; maybe they are exploring their world and gaining confidence before leaving to brave the world outside their home. Remember these birds have only been alive for a week and a half or so!  Regardless, it’s a bit like kids going off for college but returning for school breaks … nestlings may leave and return repeatedly before fully fledging. Fledging is not nearly as simple as people think it is!

Understanding the fledging process allows us to better understand the biology of grassland birds. Learning about the pressures they face in their daily lives lets us understand what threats they face and how those threats may change as people alter grasslands. Grassland birds are declining more than birds of any other habitat type across North America. Research like this is part of understanding why they are declining and what we can do to help them recover.

“Live Fast, Die Young” Lifestyle Reflected in Birds’ Feathers

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A museum specimen ready to be photographed. Photo credit: R. Terrill

Animals’ lives tend to follow a quicker tempo as they get farther from the equator—birds at more northern latitudes mature faster, start reproducing younger, and live shorter lives, probably as a way of dealing with seasonal variation in resources. A new study from The Auk: Ornithological Advances shows for the first time that this pattern also plays out in birds’ feathers, with northern birds completing their annual molt faster to keep up with the demands of life far from the tropics.

Louisiana State University’s Ryan Terrill looked at museum specimens of four bird species with ranges that span a wide swath of latitude in both the Northern and Southern Hemispheres. Slight differences in feather growth between day and night during birds’ annual molt produce visible pairs of light-colored bars, each pair representing 24 hours’ growth. Terrill could determine the rates at which individual feathers grew by measuring their spacing. He found that for all four species, individuals collected at higher latitudes had grown their feathers faster.

Terrill sees two potential explanations for this pattern, which aren’t mutually exclusive. First, where the availability of food changes with the seasons, birds may need to molt faster so that they have the necessary resources. Second, because birds at higher latitudes tend to be more invested in producing offspring than in extending their own survival, faster production of lower-quality feathers may be an acceptable tradeoff.

“Working with museum specimens was a lot of fun,” says Terrill. “One of my favorite things about museum specimens is using them in ways that other folks might not consider, and especially using them in ways for which the original collector couldn’t have known they might be useful. It wasn’t until recently that many people considered that how feathers grow might be important for birds or realized that you could measure feather growth rates on specimens, and I hope this study will publicize yet another way that museum specimens are useful for understanding birds.”

“Most aspects of avian molt, with the exception of feather-replacement sequence, are thought to be rather flexible. The timing, location, and extent of molts appear to respond quickly to environmental constraints, even within populations of the same species occurring at different latitudes, as either permanent or winter residents,” adds the Institute for Bird Population’s Peter Pyle, an expert on bird molt patterns who was not involved with the study. “Yet molt strategies remain vastly understudied compared to other avian topics such as breeding, migration, and behavioral responses. This paper shows that a fourth component of molt, feather growth rate, also appears to vary, with equatorial populations showing slower molt intensity than those of higher latitudes. The author ties this nicely in to other studies suggesting a decelerated pace of other life history traits in less seasonal environments, perhaps as a function of slower basal metabolic rates.”

Feather growth rate increases with latitude in four species of widespread resident Neotropical birds is available at http://americanornithologypubs.org/doi/full/10.1642/AUK-17-176.1.

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology published by the American Ornithological Society. The Auk commenced publication in 1884 and in 2009 was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

AUTHOR BLOG: Count me in! I am available for detection at 6 AM on May 26th

Péter Sólymos

Linked paper: Evaluating time-removal models for estimating availability of boreal birds during point count surveys: Sample size requirements and model complexity by P.  Sólymos, S.M. Matsuoka, S.G. Cumming, D. Stralberg, P. Fontaine, F.K.A. Schmiegelow, S.J. Song, and E.M. Bayne, The Condor: Ornithological Applications 120:3, August 2018.

Point count survey duration rarely changes within projects but varies greatly among projects. As more and more large-scale studies are compiling and analyzing point count data from disparate sources, standardization becomes critical, because count duration greatly affects observations. The Boreal Avian Modelling (BAM, www.borealbirds.ca) project aims to further continental scale avian conservation through the integration and analysis of point count data collected across northern North America. In order to estimate population density and population size for landbird species, data integration became a real issue for us.

Two of the main sources of variation in the observed counts have nothing to do with ecological variables of interest, such as land cover and climate, but rather are considered nuisance variables. These are point count radius and point count duration. Recognizing that most studies do not follow survey protocol recommendations aimed to facilitate data integration (see e.g. Matsuoka et al. 2014), we opted to use model-based techniques to place our variable data on a common footing.

We first tackled standardizing for varying point count radii through distance sampling (Matsuoka et al. 2012) and eventually combined this with a removal model-based correction for varying point count duration. We named the method QPAD, referring to terms of our statistical notation: probability of detection (q), probability of availability (p), area surveyed (A) and population density (D) (Solymos et al. 2013). In the present paper we assessed different ways of controlling for point count duration. As the title indicates, we performed a cost-benefit analysis to make recommendations about when to use different types of the removal model.

We evaluated a conventional removal model and a finite mixture removal model, with and without covariates, for 152 bird species. We found that the probabilities of predicted availability under conventional and finite mixture models were very similar with respect to the range of probability values and the shape of the response curves to predictor variables. However, finite mixture models were better supported for the large majority of species. We also found overwhelming support for time-varying models irrespective of the parametrization.

So what is a finite mixture model? In our case, it splits the population of birds present at a location into frequent and infrequent singers. In previous parametrizations, researchers assumed that the singing rate of the infrequent group varies with date and time, whereas frequent singers remain frequent singers independent of time of year or time of day. We compared this to an alternate parametrization that assumes that individuals change behaviour over time and switch from frequent to infrequent singing behaviour—so it is the proportion of the two groups that varies. We found that the latter assumption was favoured.

Finite mixture models provide some really nice insight into how singing behaviour changes over time and, due to having more parameters, they provide a better fit and thus minimize bias in population size estimates. But all this improvement comes with a price: Sample size requirements (or more precisely, the number of detections required) are really high. To have all the benefits with reduced variance, one needs about 1000 non-zero observations to fit finite mixture models—20 times more than needed to reliably fit conventional removal models. This is much higher than previously suggested minimum sample sizes.

All of our findings indicate that lengthening the count duration from 3 minutes to 5-10 minutes is an important consideration when designing field surveys to increase the accuracy and precision of population estimates. Well-informed survey design, combined with various forms of removal sampling, is useful in accounting for availability bias in point counts, thereby improving population estimates and allowing for better integration of disparate studies at larger spatial scales. To this end, we provide our removal model estimates as part of the QPAD R package and the R functions required to fit all the above outlined removal models as part of the detect R package. We at the BAM project and our collaborators are already utilizing the removal model estimates to correct for availability bias in our continental and regional projects to inform better management and conservation of bird populations. Read more about these projects in our annual report.