Tag Archives: nesting

Stress in the nest can have lifelong effect

(The Norwegian University of Science and Technology, Science Daily 16 August 2017)

Why do some sparrows hatch six chicks while others don’t hatch any? How does upbringing affect the remainder of their lives? Physiological stress in the nest can actually affect birds’ DNA and possibly their lifespan.

On average, a mere 10 to 20 per cent of sparrow nestlings survive until the next breeding season. But the survival rate varies between different parents, according to Thomas Kvalnes and Michael Pepke Pedersen at the Norwegian University of Science and Technology’s (NTNU) Centre for Biodiversity Dynamics (CBD).

In order to learn more about this variation, they’re studying birds by banding them.

Good conditions in NTNU birdhouse

At the NTNU Gløshaugen campus in Trondheim, Kvalnes and Pedersen have been following a pair of Eurasian blue tits, which eventually laid ten eggs and were incubated for two weeks. Then the real work started for the parents. No fewer than nine chicks hatched and they all wanted to eat — at the same time.

The blue tit chicks — which are part of the sparrow family — grew enormously fast during the nesting period, growing from less than one gram at hatching to 10 to 12 grams at around 15 days old. This requires a lot of food. The parents in the NTNU birdhouse seem to have access to good nutrition, because all nine young were alive and growing normally when they were 12 days old.

Banding for research

By the age of 12 days, the young had a lot of feathers and were able to regulate their body temperature well. They were also small enough not to get scared and fly out when the lid on the birdhouse was opened. This is important to think about when banding chicks, because the bands must not adversely affect the birds.

The researchers banded all nine baby birds with metal rings, each having a unique identity number. This allows researchers to recognize the individuals later and to follow their development throughout their lives.

Banding is a widely used method by researchers at the NTNU’s Centre for Biodiversity Dynamics.

How does upbringing affect the rest of a bird’s life?

New research suggests that the first days and weeks have a big impact on how the rest of a bird’s life unfolds. In some clutches, the young get a lot of food and grow fast, whereas in others the chicks face tougher competition or the nest is more exposed to the weather. However, conditions in the nest can actually leave a genetic impression in the birds, more specifically on the ends of the chromosomes that make up the DNA.

The telomeres (from Greek, meaning “end pieces”) that protect the DNA from breaking down are found here, say Kvalnes and Pedersen.

“Each time a cell divides, the DNA must be copied, but the entire DNA sequence cannot be copied, and that impacts the telomere structures, which get shorter after each copying. At the same time, the telomeres wear down if exposed to oxidative or physiological stress, the researchers say.

Molecular thread of fate?

When the telomeres become too short, cell function may become impaired and the entire organism may be affected by age-related illnesses. Some studies have shown that birds’ telomere length can predict how long they will live — a bit like the thread of fate that is clipped by the Norns in Norse mythology and decides the length of human lives.

The most rapid shortening of the telomeres in life occurs when the young chicks grow fast. At CBD, researchers are investigating the connection between sparrow telomeres and their life stories. The researchers follow them from their time in the nest until they become parents themselves — and perhaps grandparents — until their death.

Telomeres in birds and humans

Much of our understanding of telomeres comes from studies of animals in captivity or laboratories, but there’s a lot we don’t know about how these fundamental physiological processes work in typical natural circumstances. CBD researchers hope to help answer these questions.

“The telomeres in birds are identical to those found in humans and all other vertebrates, and they speak to our common origin. In fact, telomere mechanisms exist in all organisms except simple bacteria and archaea. So it’s conceivable that we’ll be able to transfer our knowledge of telomere dynamics in birds to many other organisms,” the researchers say.

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Prairie-Chicken Nests Appear Unaffected by Wind Energy Facility

CONDOR-17-51 L Powell

(AOS 9 August; Photo: L. Powell)

Wind energy development in the Great Plains is increasing, spurring concern about its potential effects on grassland birds, the most rapidly declining avian group in North America. However, a new study from The Condor: Ornithological Applications suggests that for one grassland bird species of concern—the Greater Prairie-Chicken—wind energy infrastructure has little to no effect on nesting. Instead, roads and livestock grazing remain the most significant threats to its successful reproduction.

Prairie-chickens are thought to avoid tall structures such as wind turbines because they provide a perch from which raptors can hunt. To learn more, the University of Nebraska–Lincoln’s Jocelyn Olney Harrison and her colleagues gathered data on the effects of an existing small wind energy facility (36 turbines) in Nebraska. They captured 78 female prairie-chickens at breeding sites, or leks, ranging from less than a kilometer from the wind energy facility to more than twenty kilometers away, and fitted the birds with transmitters to track them to their nests. Monitoring their nesting success and collecting data on the habitat characteristics of each nest site, they found little evidence that the wind energy facility affected nest site selection or a nest’s chances of survival. Instead, vegetation characteristics, driven by land use practices such as grazing, had the greatest influence on prairie-chicken nests. Birds also avoided nesting near roads.

“When comparing previousw studies to our own, it appears that the effects of wind energy facilities on prairie grouse are often site- and species-specific,” says Harrison. “Therefore, it’s important to consider the results of our study in the context of the size and location of the wind energy facility, as well as the prairie grouse species investigated. We suggest that livestock grazing and other grassland management practices still have the most important regional effects on Greater Prairie-Chickens, but we caution future planners to account for potential negative effects of roads on nest site placement.”

Private landowners were key to completing the study, Harrison adds. “Our radio- and satellite-tagged Greater Prairie-Chickens made larger than expected movements while we were tracking them, which led us to require permission from new land owners on almost a weekly basis during our field seasons. Landowners throughout our field study area were always extremely welcoming and helpful, and genuinely interested in our work. Our project was a success due to more than 50 landowners who granted us access to their private lands.”

Härfågel häckar i Skåne

(SOF 2017-08-04)

Härfågeln räknas (tillsammans med kungsfiskare, biätare och blåkråka) till de fyra “praktfåglar” som många av oss medelålders och äldre fågelskådare drömde om att någon gång få uppleva när vi bläddrade i den klassiska “Fåglarna i färg” av Sigfrid Durango. För många har det kanske också blivit verklighet, eftersom Sverige relativt ofta besöks av härfåglar (främst söderifrån). Chanserna lär dessutom öka framöver, då arten förutspås flytta sitt utbredningsområde norrut i takt med klimatförändringar.

Under 1800-talet var härfågeln en ganska vanlig häckfågel i sydöstra Sverige, men i början av 1900-talet försvann den. På 1980-talet fanns åter häckande härfåglar på Öland och Gotland och även om antalen förefaller ha blivit betydligt färre på 2000-talet så konstateras häckningar då och då. I Skåne har häckningar varit extremt sällsynta, så nyheten som släpptes igår är något alldeles extra!
Nu har nämligen en häckning offentliggjorts vid Ravlunda skjutfält i Skåne. Anledningen till att man går ut med en så exklusiv häckning är att ungarna nu är flygga och bedöms tåla lindrig form av störning. Vår generella inställning är att så många som möjligt ska kunna njuta av såväl vanliga som ovanliga fåglar i Sverige, utan att fåglarna tar skada. Besökare förväntas givetvis lämna vederbörligt hänsynsavstånd. Uppgifter om fyndet finns bl.a. på Artportalen.
Härfågeln häckar i jordbruksbygder, ofta i närheten av öppna betade marker, där den oftast letar efter småkryp i marken (eller ko-/hästspillning) med sin långa och böjda näbb. Äggen läggs gärna i trädhål, men i mer trädlösa landskap kan stenmurar vara ett fullgott alternativ.

These birds are trapped between predators and rising sea levels

seaside sparrow fledglings Mary Beth Griggs July 12, 2017

Probing its beak into the soft mud, looking for seeds or insects, the Seaside Sparrow is a common sight on the southeastern coasts of the United States.

Biologist Elizabeth Hunter started studying the small birds as a part of her dissertation at the University of Georgia. She wanted to know how sea level rise—which is already happening in Georgia at a rate of 3 mm/year—would threaten the sparrows. Then, she noticed something surprising.

“Over three years of collecting field data on Seaside Sparrow nesting success, I noticed that many more nests were being eaten by predators than being flooded by high tides,” Hunter said in an e-mail to Popular Science.

Not wanting to overlook an important threat to the population, Hunter, now at the University of Nevada, Reno, decided to create a mathematical model that would take both predation and sea-level rise into account. She found that while flooded nests were a threat to Seaside Sparrows, they were far more likely to build their nests lower in shrubs where predators were less likely to reach them, even if that meant their nest might get flooded more often.

Hunter says that sea level rise has made the risk of Seaside Sparrow nests flooding five to ten times more likely now than in the 1980’s. When a nest floods while empty, or when a few eggs are tucked inside, the flooding is generally manageable. So long as the eggs don’t float away, the sparrows can rebuild.

“The danger is when the nest has nestlings. Nestlings stay in the nest for 10 days after they hatch until they fledge, and if the nests floods while they are still in it, they can drown,” Hunter said. “Adults themselves aren’t really affected by flooding, but they do have to expend more effort to make a new nest and care for eggs and hatchlings if a nest is lost.”

In addition to the threat of the rising sea, the sparrows face assaults from the sky and the land. Fish crows, grackles, red-winged blackbirds, and marsh wrens attack from above, while raccoons, mink, and marsh rice rats mount a ground assault.

During seasons when predator activity was high, the sparrows kept their nests low to the ground. When they lost a nest due to flooding, they built higher, but the predator pressure weighed heavier in their choices than the flooding experience. Caught between gnashing teeth and the deep blue sea, Hunter estimates that predators are about seven times more important than sea level rise in Seaside Sparrows choosing their nesting location. Her research was published today in The Condor: Ornithological Applications.

Luckily, even though Georgia is expected to get one meter (three feet) of sea level rise by 2100—further squeezing the seaside sparrow habitat—there is hope. Hunter says that there is a chance that if humans can lessen the predator impact by putting fencing or modified cages around nesting areas, they might be able to encourage sparrows to move to higher ground. The research could also help other wildlife management teams plan out a future that keeps other birds living high and dry.

Danmark får ingen unge kongeørne i år

Jan Skriver 12 juli 2017)

De fire ynglende kongeørnepar i Nordjylland, der huser den samlede danske bestand, har i år deres ringeste ynglesæson nogensinde. For første gang i knap 20 år glipper det med frugtbarhed blandt de store rovfugle. Koldt vejr, alderdom og æggetyve blandt rovdyr kan være blandt forklaringerne på den golde sæson

Efter knap to årtier med frugtbarhed og stor stabilitet på hjemmefronten blandt Danmarks ynglende kongeørne ender 2017 som en sæson uden nyt liv.

Det er formentlig et sammenfald af uheldige omstændigheder, som bevirker, at der ikke kommer unge danske kongeørne på vingerne denne sommer. Og der er næppe grund til panik på artens vegne de kommende år, mener ornitologen Tscherning Clausen, der er Dansk Ornitologisk Forenings (DOF) artscaretaker for kongeørnen. Han samler alle data om ørnene, og sammen med fire redekoordinatorer holder han et vågent øje med udviklingen i bestanden.

”Indtil i år har de danske kongeørne været usædvanligt frugtbare, hvis man for eksempel sammenligner med deres svenske artsfæller. De danske ørne har indtil 2017 fået unger på vingerne 18 år i træk. At det glipper i år, kan måske skyldes et meget koldt vejrlig netop i den periode, hvor ørneæggene klækkede. Det kan også spille ind, at alderen begynder at trykke hos i hvert fald et af parrene. Og måske spiller rovdyr som mårer en rolle som æggerøvere. Vi har på ørne-webben hos DOF set, at en husmår er i stand til at kravle op i en havørnerede og æde æggene. Det samme kan ske for kongeørne”, siger Tscherning Clausen, der påpeger, at store rovfugle ofte springer en sæson over, uden at det nødvendigvis påvirker deres tilstedeværelse året efter på et givent territorium.

Svenske ørne holder pauser

”Fra Sverige ved vi, at kongeørne ganske ofte tager en pause med ynglen. Nogle gange kan de springe en sæson over hvert andet eller tredje år. Her må vi sige, at de danske ørne til sammenligning har været ekstremt stabile og frugtbare lige siden artens indvandring. For eksempel har ørneparret i Høstemark Skov i Lille Vildmose fostret en flyvefærdig unge 14 år i træk. I år er første sæson, det glipper for parret, hvor fuglene er omkring 20 år gamle. Selv om kongeørne formentlig kan blive op imod 25-30 år i naturen og i fangenskab endnu ældre, kan alderen måske begynde at resultere i en ringere frugtbarhed hos Høstemarkfuglene”, siger Tscherning Clausen.

Lovende start, skidt finale

Tidligt på sæsonen 2017 så det ellers lovende ud for de fire kongeørnepar i henholdsvis Store Vildmose, Hals Nørreskov samt Høstemark Skov og Tofte Skov i Lille Vildmose, oplyser DOF’s artscaretaker.

Det nye ynglepar, der i 2016 etablerede sig i Store Vildmose, byggede i år en ny rede, men parret opgav tidligt 2017-sæsonen. I Hals Nørreskov, hvor ørnene har ynglet siden 2007, opgav parret i begyndelsen af juni.

Også i Tofte Skov, hvor et nyetableret par byggede rede, og i Høstemark Skov, hvor de erfarne ørne residerer, tegnede det godt tidligt på foråret.

”Fælles for alle parrene har været, at de formentlig har nået at lægge æg og ruge en tid, inden det er gået galt. På sin vis er det ikke overraskende, at de nyetablerede ynglepar i Store Vildmose og det i Tofte Skov mislykkes med familielivet. Det ser man ofte hos store rovfugle. Men vi er overraskede over, at de veletablerede og meget stedfaste ørne i Hals og Høstemark fejler i år”, siger Tscherning Clausen.

To nordjyske revirer på vej

To af fire unge kongeørne, som i forskningens tjeneste er udstyret med GPS-sendere, sender fortsat data om deres færden i landskabet.

Begge disse fugle giver på sin vis løfter om fremtidig frugtbarhed, for de opholder sig meget stabilt i velegnede yngleterræner for kongeørne.

”Den ene af de GPS-mærkede ørne har længe holdt til i moserne nord for Frederikshavn, hvor Råbjerg Moses store uforstyrrede flader må betragtes som et realistisk kommende fast revir for kongeørn. Også den anden GPS-ørn har realistiske muligheder for at etablere sig i det område, hvor den længe har holdt til. Det er nemlig i Hals Sønderskov, der ligesom Hals Nørreskov må siges at være et gæstfrit ørneteræn”, siger Tscherning Clausen.

Nye ørneterræner i sigte

Trods den ringe sæson 2017 har de danske kongeørne gjort deres til at give arten luft under vingerne. I alt er der fostret 37 udfløjne unger i Danmark i perioden 1998-2016. Der menes at være plads, føde og territorier til måske en halv snes kongeørnepar i det danske landskab.

Ovstrup Hede ved Herning og Borris Hede øst for Skjern er realistiske mulige ynglesteder. Også Randbøl Hede og Harrild Hede i Sydjylland, der tidligere har haft besøg af kongeørne, er potentielle yngleområder.

Der skønnes også at være muligheder for flere par kongeørne i Thy, Hanherred, og i de store hedeplantager i Midtjylland. Også Vendsyssel kan komme yderligere med som ørneterræn, blandt andet i Jyske Ås-området.

Nesting in cavities protects birds from predators—to a point

Nesting in cavities protects birds from predators -- to a point
(Physorg 12 June 2017; Photo M. Arndt)

Nesting in cavities provides birds with some protection from predators—but it isn’t foolproof. A new study from The Auk: Ornithological Advances explores how Poland’s cavity-nesting Marsh Tits deal with predator attacks and finds that while tactics such as small entrances and solid walls do help, adaptations like this can only take the birds so far.

Wrocław University’s Tomasz Wesołowski has spent nearly thirty years monitoring Marsh Tit nest cavities in Poland’s Białowieża Forest, comparing nests that are destroyed with nests that are attacked but survive. He has found that a nest’s chance of survival depends on the predator’s technique—broods are least likely to survive (10%) when the predator manages to get into the cavity through the existing entrance, more likely (29%) when the predator uses its paws or beak to pluck out the nest contents, and most likely to survive (39%) when the predator tries to enlarge the opening or make a new one. Tits’ antipredator tactics vary in their effectiveness depending on the predator; attacks by Great Spotted Woodpeckers were successful only 60% of the time, while forest dormice were 100% successful.

The results show that despite the constant pressure of natural selection, Marsh Tits can only improve their antipredator tactics so much—there are limits to adaptation. Small, narrow entrances don’t work against small predators and are only effective when combined with cavity walls made of solid (not decomposing) wood; nests that were deep in a cavity, out of reach of the entrance, are safest, but birds seldom place their nests that way, suggesting that cavities that are too deep may cause other problems for Marsh Tit parents.

The Białowieża Forest, one of the last remaining tracts of old-growth forest in Europe, is an ideal place to study cavity-nesting birds, full of cavities of every size and shape for Marsh Tits to choose from. However, the fieldwork was not without its difficulties. “The Białowieża Forest still contains fragments of primeval origin,” says Wesołowski. “The work is challenging, as the old-growth stands are very tall. Marsh Tits breed at very low densities, and on average one has to search five to seven hectares of this forest to find a single breeding cavity. It requires much patience and determination.”

“To understand the evolution of nesting behaviors, many ornithologists attempt to quantify the trade-offs that birds face in warding off nest predators. Usually we do this by comparing nests that fail versus nests that succeed, but that approach is limited because we can’t tease apart the multiple factors, including chance, that contributed to making a nest successful,” according to Kristina Cockle of the National Scientific and Technical Research Council of Argentina (CONICET), an ornithologist not involved with the study who has worked extensively on nest cavities. “The new study by Wesołowski compares, instead, nests that were depredated to nests that were attacked but survived. With this approach, the author was able to identify the physical attributes of tree cavities that foiled a suite of nest attackers from woodpeckers to dormice.”

Late-nesting birds, bees face habitat threat

(University of Exeter 12 june 2017)

Bird and bumblebee species that nest late in the year are suffering more from the destruction of habitats, new research suggests.

With habitats such as hedgerows and hay meadows in decline in many countries, fewer nest sites are available — leading to more competition.

The University of Exeter study found that species which nest late — in April or May rather than February or March — are declining more than other species, with the larger birds and bumblebees worst affected.

The research goes some way to unravelling the mystery of why numbers of some closely related species — like the thriving chaffinch and the struggling goldfinch — are moving in different directions.

“The effects of habitat destruction are complicated, but we must understand them if we are going to save threatened species,” said Dr Andrew Higginson, of the University of Exeter.

“The loss of nest sites due to damage to the environment is an important cause of species extinctions.

“Ecologists understand why some groups of species are declining more, such as why farmland species are declining more than woodland species.

“But an enduring mystery is the big variation in the declines of closely related species.

“Fighting over nest sites may be part of reason — when nest sites are hard to come by, the species that will suffer most are that nest later in the year.”

The study, published in the journal Behavioural Ecology and Sociobiology, combines mathematical modelling with an analysis of population changes in 221 bird and 43 bumblebee species worldwide.

A mathematical model of searching for and fighting over nest sites was created. The model predicted when different species should fight for nest sites depending on their size, timing that they nest and the quality of the nest site.

The model shows that if animals are still doing what they did before habitat damage caused by decades of agricultural intensification, then large, early-nesting species such as great tits will be fine, but late-nesting species such as tree sparrows will decline.

“Surprisingly, the model predicts that the large species will suffer much more from being late nesters,” said Dr Higginson. “This happens because large species know they can beat small species if they find a good nest site.

“So while smaller species settle for what they can find, the larger ones keep looking and end up failing to breed.” Dr Higginson tested this prediction by collecting data on the declines of birds and bees over the 20th Century, their body size, and when and where they nest. Birds were in North America and Europe, and bumblebees were in five countries.

In all these data sets, the predictions of the model were supported. This suggests that the model is correct about how animals behave when looking for nest sites, and that nest sites are important in determining difference between species in their losses.

Speaking about the broader implications of the study, Dr Higginson said: “There are many resources other than nest sites which species share.

“Rapid reductions in the abundance of these resources will result in unprecedented conflicts that reduce the potential for species co-existence.”he study suggests that conservation focus might need to be reconsidered.

“So far, conservationists have focussed on providing enough food for animals such as birds and bees, such as the important bee-friendly flowers in gardens,” Dr Higginson said.

“These results suggest that to save rare species we need more focus on making sure that they have enough places to nest.”

He added: “To save bumblebees, people could let part of their garden grow wild between early spring and late summer.”

The paper is entitled: “Conflict over non-partitioned resources may explain between-species differences in declines: The anthropogenic competition hypothesis.”