AUTHOR BLOG: A new hummingbird species in Ecuador

Juan Freile

Linked paper: A striking, critically endangered, new species of hillstar (Trochilidae: Oreotrochilus) from the southwestern Andes of Ecuador by F. Sornoza-Molina, J.F. Freile, J. Nilsson, N. Krabbe, and E. Bonaccorso, The Auk: Ornithological Advances 135:4, October 2018.

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Adult male (above left, center right), adult female (below), and immature male (above right) Oreotrochilus cyanolaemus. Image credit: P. Greenfield.

Last year a new hummingbird species was unexpectedly discovered on a seldom-visited mountain top in southern Ecuador. A brief visit to the rocky outcrops of Cerro de Arcos in the southern province of El Oro produced a photographic record that rang a bell: a mysterious immature male clearly assignable to the genus Oreotrochilus, the hillstars, which included six species at the time. A few days later, an adult male was captured in another photo, and a week after that, several males and females were observed and a handful collected for scientific purposes.

Such an outstanding discovery needed a thorough assessment to understand the taxonomic status and phylogenetic relationships of the putative new species and their evolutionary implications for the genus Oreotrochilus. This genus is remarkable in being the one that reaches the highest elevations: records above 4,500 meters, with a mean of 3,600 meters above sea level. As such, these hummingbirds need a very special set of physiological and behavioral adaptations to feed on the scarce nectar resources available. One plant in particular is extremely important for the hillstars—the spiny-leaved Chuquiragua, with its fire-orange flowers.

The newly discovered hillstar of southern Ecuador is not an exception in its feeding associations. In fact, its geographic range seems to be shaped by the availability of Chuquiragua in a very restricted region between the geographic ranges of the Ecuadorian Hillstar, Oreotrochilus chimborazo, found in Ecuador and extreme southern Colombia, and the Green-headed Hillstar, Oreotrochilus stolzmanni, found in Peru and extreme southern Ecuador.

The latter species is likely the closest relative to the new species, sharing an overall plumage pattern and being very similar genetically. But a single striking characteristic sets them apart: the Green-headed Hillstar has a glittering lime-green throat patch, or gorget, whereas the gorget in the new species is a glittering deep blue. Given that gorgets are likely used in courtship displays by males, the strikingly different color suggests that reproductive isolation is effectively segregating these taxa.

Being extremely restricted in distribution, confined to a few mountain tops where habitat degradation is dramatic, the conservation status of this new hillstar seems critical. No conservation projects exist across its tiny range; on the contrary, the agricultural boundary is progressing, cattle graze free in the few natural grasslands that remain, burns are frequent every windy summer, and not a few mining concession cover the area. Urgent research and conservation actions are on the way, but there is little time left.

Newly Discovered Hummingbird Species Already Critically Endangered

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A male Blue-throated Hillstar. Photo credit: F. Sornoza-Molina

In 2017, researchers working in the Ecuadorian Andes stumbled across a previously unknown species of hummingbird—but as documented in a new study published in The Auk: Ornithological Advances, its small range, specialized habitat, and threats from human activity mean the newly described Blue-throated Hillstar is likely already critically endangered.

Hillstars are unusual among hummingbirds—they live in high-elevation habitats in the Andes and have special adaptations to cold temperatures. Francisco Sornoza-Molina of Ecuador’s Instituto Nacional de Biodiversida, first observed and photographed a previously unknown hillstar during fieldwork in southwest Ecuador in April 2017. After this first expedition, Sornoza-Molina engaged fellow researchers Juan Freile, Elisa Bonaccorso, Jonas Nilsson, and Niels Krabbe in the study of this possible new species, returning in May to capture specimens and confirm the finding. They dubbed the new species Oreotrochilus cyanolaemus, or the Blue-throated Hillstar, for its iridescent blue throat.

The Blue-throated Hillstar is found only along bush-lined creeks in an area of about 100 square kilometers, and the researchers estimate there are no more than 750 individuals, perhaps fewer than 500. Threats to its habitat include fire, grazing, and gold mining, and it meets the criteria to be considered critically endangered. “Complete support from national and international conservation agencies is needed in order to save this species,” says coauthor Francisco Sornoza-Molina. “The action plan for the conservation of this bird is creating a network of protected areas along its geographic range.”

“The hillstar hummingbirds occur in the most rugged, isolated, and inaccessible parts of the Andes, where they roost in caves, forage on the ground, and spend half their lives in hypothermic torpor, so the discovery of a new species in this group is incredibly exciting. This striking discovery confirms that life in the high Andes still holds many secrets to be revealed,” according to the University of New Mexico’s Christopher Witt, a hummingbird expert who wasn’t involved in the study. “The location is fitting for a new species of hillstar, because it’s a remote, high mountain range that is isolated and is sandwiched between the ranges of two other hillstar species. The authors did a thorough job comparing the new form to its relatives in every respect.”

A striking, critically endangered, new species of hillstar (Trochilidae: Oreotrochilus) from the southwestern Andes of Ecuador is available at http://americanornithologypubs.org/doi/full/10.1642/AUK-18-58.1.

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.

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: The real story behind murres’ pear-shaped eggs

Tim Birkhead

Linked paper: The pyriform egg of the Common Murre (Uria aalge) is more stable on sloping surfaces by T.R. Birkhead, J.E. Thompson, and R. Montgomerie, The Auk: Ornithological Advances 135:4, October 2018.

murre eggFor the past six years, Jamie Thompson, Bob Montgomerie, and I have tried to understand why murres produce a pear-shaped (pyriform) egg.

It started one evening in 2012 when I watched a well-known TV presenter take a murre’s egg from a tray of birds’ eggs in a museum. “The reason it is this shape,” he said, “is so that if it is knocked, it will spin on its axis rather than rolling off the cliff ledge.” He demonstrated this by spinning the egg.

I was appalled. That idea was nonsense and had been dismissed over a century earlier. Yes, if you take an empty eggshell you can indeed lie it on its side and spin it like a top on its side. But a murre egg full of yolk, albumen, and a developing embryo will not spin like that without undue force.

Having offered to send the presenter the papers pointing out why the spinning-like-a-top idea was wrong, I had a sudden crisis of confidence, and decided I had better re-read those papers myself.

I soon realized that the more widely accepted view — that a pyriform egg rolls in an arc and thereby minimizes the risk that it will fall off the breeding ledge — was not very convincing either. The rolling-in-an-arc idea gained support initially by some experiments in the 1960s using model eggs (made from plaster of Paris). But it was later found that model eggs simply do not roll like real eggs. Subsequent experiments with real murre eggs provided no convincing evidence for the rolling-in-an-arc idea, either.

What’s more, incubating murres invariably orient their egg with its blunt end directed up the slope, in towards the cliff, so that if the egg does roll, it will roll out to the edge. If the purpose of the pyriform egg was to prevent it from rolling off the ledge, then it would more sensible for the parent to orientate the egg the other way.

We decided to re-investigate, thinking explicitly about the selection pressures that might influence the shape of a murre’s egg.

We had two ideas. First, murres are poor flyers that breed at high density. As a result, crash landings onto incubating birds are common, so perhaps a pyriform shape confers greater strength and resilience against impacts. That proved to be a difficult idea to test.

Our second idea rested on the observation that murre ledges are filthy with excrement. Perhaps the pyriform shape enables an egg to keep its blunt end clean such that the pores for air exchange do not become blocked. We found that the density of pores on the blunt end of the egg was relatively high and, if you look at the distribution of dirt on murre eggs, most of it is on the pointed end. These results are consistent with the dirt hypothesis. However, it wasn’t clear whether avoiding dirt or avoiding damage from impacts were sufficiently strong selection pressures to have produced the shape.

Then, while climbing on murre ledges in 2017, I had a sudden thought. Perhaps the pyriform shape allows a murre’s egg to rest stably on the sloping ledges that murres often breed on. I had fresh murre eggs and Razorbill eggs (which are much less pointed and more elliptical in shape) to hand, and I tried placing them on a 30o rock slope. The murre egg rested there immediately, the Razorbill egg rolled off (into my hand, of course), and, indeed, there was no way I could position the Razorbill egg stably on that slope.

My colleague Jamie was climbing with me, so I called him over, said “Watch this!”, and demonstrated again. Same result. Then, together with Bob Montgomerie, we devised a series of tests to establish just how stable murre and Razorbill eggs are across a range of egg shapes on slopes of different steepness. We quantified egg shape using a new approach (Biggins et al. 2018). We then conducted two experiments, one using a moving slope and the other using three static slopes at 20o, 30 o and 40 o. We tested to see at what angle each egg would begin to roll on the moving slope and how successful we were at stably positioning each egg on the static slopes.

The results are clear. The more pyriform the egg, the more stable and less likely to roll out of place it is. Our results are NOT about how an egg will roll when it becomes unstable, but about whether it begins to roll in the first place, either when knocked or during changeovers. Our results indicate that the stability of a pyriform egg also makes it easier and safer for murres to manipulate (with their beak, wings and feet) their eggs during incubation and changeovers.

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Links:

I started studying Common Murres (common guillemots in the UK) Uria aalge in 1972, on Skomer Island, off the coast of Wales, UK.  I have kept that study — whose main thrust is population monitoring — going ever since: www.justgiving.com/guillemotsskomer

The video describing our murre egg study is here:  https://youtu.be/e-189LIYa0Y

Tim Birkhead academic website: https://www.sheffield.ac.uk/aps/staff-and-students/acadstaff/birkhead

 

Other relevant papers:

Biggins, J. D., Thompson, J. E. & Birkhead, T. R. 2018. Accurately quantifying the shape of birds’ eggs. Ecology and Evolution 8: in press.

Birkhead, T. R. 2017. Vulgar errors — the point of a Guillemot’s egg. British Birds 110: 456-467.

Birkhead, T.R., Thompson, & J. E., Biggins, J. D. 2017. The point of a guillemor’s egg. Ibis 159: 255-265.

Birkhead, T. R., Thompson, J. E. & Biggins, J. D. 2017.  Egg shape in the common guillemot Uria aalge and Brunnich’s guillemot U. lomvia: not a rolling matter? Journal of Ornithology 158: 679-685.

Birkhead, T.R., Thompson, J. E., Biggins, J. D. & Montgomerie, R. 2018.  The evolution of egg shape in birds: selection during the incubation period. Ibis, in press.

Arctic Seabird Populations Respond to Climate Change

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Alaska’s Black-legged Kittiwakes are among the seabird species impacted by climate change. Photo credit: Marc Weber, USFWS

Seabirds such as gulls can be key indicators of environmental change as their populations respond to shifts in their ocean habitat over time. A new study from The Auk: Ornithological Advances investigates how several species have responded to changing environmental conditions in the Arctic over the last four decades. The authors find that a warming ocean is directly and indirectly affecting seabird populations in Alaska.

The University of Idaho’s Holly Goyert (now at the University of Massachusetts) and her colleagues used mathematical models to explore relationships between large, long-term datasets covering climate fluctuation, zooplankton abundance and distribution, and populations of several seabird species in the waters off Alaska from 1974 to 2014. They found that declines in populations of an Arctic gull called the Black-legged Kittiwake are tied to deteriorating zooplankton productivity, while their cousins the Red-legged Kittiwakes, also declining, are more sensitive to warming ocean surface temperatures. Not every seabird is in trouble, though—Common and Thick-billed Murres, relatives of puffins, have proved resilient to changing conditions and may even be benefitting.

This study is the first attempt to explain how climate and habitat variability affect seabird population dynamics across such a large scale. “Our hope is that these results will be used in a proactive approach to seabird conservation, and that measures will be taken to prevent populations from declining to small sizes. For example, although Black-legged Kittiwakes are one of the more abundant gulls in the world, their populations are undergoing significant declines, which calls their global status into question,” says Goyert. “Our paper suggests that the deterioration of food web resources such as krill, which is related to warming oceans, has contributed to these declines.”

“Mass seabird deaths and breeding failures in recent years have the scientific community puzzled, and both appear to be climate-related,” according to Melanie Smith, Audubon Alaska’s Director of Conservation Science, who was not involved in the study. “This study is an important step in clarifying the effects of changing climate on seabird population dynamics across Alaska. We can use what we’ve learned here to design detailed monitoring and to better anticipate population declines, improving managers’ ability to protect vulnerable species.”

Effects of climate change and environmental variability on the carrying capacity of Alaskan seabird populations is available at http://www.bioone.org/doi/full/10.1642/AUK-18-37.1.

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. The Auk has the #1 average Journal Impact Factor for the past 5 years for ornithology journals.