Tag Archives: nesting

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.”

Højvande gav massedød blandt Vadehavets ynglefugle


En nyklækket havterne overlever ikke et højvande foto Jan Skriver WEB

(Jan Skriver 9 juni 2017)

Terner og vadefugle i hundredvis mistede æg og unger, da et ekstremt højvande natten mellem onsdag og torsdag oversvømmede Vadehavets kystnære kolonier. Det gik blandt andet ud over Danmarks største bestand af sjældne hvidbrystede præstekraver og truede dværgterner. Voldsom færdsel af turister tvinger fuglene længere ud, så de bliver mere udsatte for højvande. Men fuglene bør beskyttes bedre, mener ornitolog fra Fanø.

En storm og en ekstrem høj vandstand natten mellem onsdag og torsdag i denne uge har forårsaget ragnarok og massedød blandt flere af Vadehavets og marskens sårbare fuglearter.

Det er gået hårdt ud over havterner, dværgterner, klyder, strandskader og navnlig de hvidbrystede præstekraver, der har deres absolut vigtigste danske ynglepladser på Rømø og Fanø.

– Højvandet var ekstremt, og der er formentlig tale om den højeste vandstand, vi har set i vadehavsregionen på denne tid af året i 40-50 år. For de fuglearter, der yngler udenfor digerne, på strandene og højsanderne, har ødelæggelsen været total. Hundreder af havterner, dværgterner og klyder fik i løbet af nattens højvande, der kulminerede ved 2-tiden, deres reder med æg eller unger oversvømmet, siger ornitolog og naturvejleder, Kim Fischer, fra DOF Sydvestjylland.

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Breeding pairs of birds cooperate to resist climate change

(Physorg 5 June ; Photo: Juan. A. Amat )

Most bird chicks need parental care to survive. In biparental species the chicks have greater chances of success if both parents participate in this task, especially under hostile situations. An international team of scientists has revealed that when temperatures rise, males and females in pairs of plovers shift incubation more frequently.

Climate change causes ecological variation and affects the lives of animals. The ever-earlier springs and later autumns caused by rising temperatures cause changes to animals’ physiology, breeding seasons and even population distributions. However, little is still known about how animals behave in response to these disturbances.

A team of scientists, working in collaboration with the Doñana Biological Station (EBD-CSIC), has studied the influence of climate change on incubation in plovers (Charadrius spp.), a genus of shorebirds spread over six continents, with a total of 33 species.

Many plover species nest on the ground in sites where there is no plant cover to detect more easily approaching predators, but where their nests receive direct sunlight.

“This can represent a significant challenge,” as indicated to SINC by Juan A. Amat, a researcher at the EBD and one of the authors of the study, which was published recently in the journal Global Ecology and Biogeography.

The scientist adds that the situation can become complicated for birds in the middle of the day, “when incubating adults may not be able to tolerate the high temperatures.” Typically, the optimum temperature adults provide for embryonic development is 35-39 ºC.

“In many bird species where both mates participate in incubation, one sex, generally the female, incubates by day, while the other (the male) does it by night,” Amat explains. However, under hot conditions greater cooperation would be needed between males and females.

Males participate in daytime incubation

One solution under changing climates would be to shorten the duration of incubation shifts between the sexes. The paper, which was led by the University of Bath (United Kingdom), analysed the behaviour of 36 populations of 12 plover species. Its results reveal that male plovers assist the females during daytime incubation.

“Males’ participation in daytime incubation increases both with ambient temperature and with as the variability of maximum temperatures during the incubation period,” the expert stresses.

The research demonstrates that a rise in temperature changes these bird pairs’ behaviour and their daily routine in terms of nest attendance. “This flexibility of parental cooperation would facilitate responses to the impact of climate change on populations’ reproductive biology,” explains Amat, who considers that the reason behind the male’s increased help is the need to better protect the embryos from extreme conditions.

Previous studies have confirmed that environmental instability has an influence on the early stage of reproduction and the lives of birds, and that unpredictable variations in the environment also affect how bird pairs cooperate in caring for their offspring. The conclusion of this new paper is that climate variations strongly influence parental cooperation.

Sea level rise may drive coastal nesting birds to extinction

Sea level rise may drive coastal nesting birds to extinction

(Australian National University 1 June 2017; Photo: Andreas Trepte)

Rising sea levels and more frequent flooding events may drive coastal nesting birds around the world to extinction, a team of international researchers say following their 20-year study of Eurasian oystercatchers.

Lead researcher Dr Liam Bailey from The Australian National University (ANU) said one of the main reasons for the strong decline in birds that used coastal habitats was because they had shown no response to tidal floods, which are predicted to become more frequent and severe due to climate change.

He said this view was corroborated by other international research.

“Sea level rise and more frequent flooding are major drivers of this steep decline in coastal birds,” said Dr Bailey, a PhD graduate from the ANU Research School of Biology.

“Our study species, the Eurasian oystercatcher, lives in an area where flooding is becoming more common, posing a threat to the survival of the population.

“Our study found no evidence that Eurasian oystercatchers have increased the elevation of their nests, even among birds that lost a nest during a flood. Factors including the presence of predators or unsuitable vegetation might discourage birds from nesting higher.”

The team will investigate other possible strategies that birds may use to avoid flooding, such as encouraging birds to lay their nests earlier in the year when floods are less common.

A recent study using thousands of bird surveys along the east coast of the United States found consistent declines in coastal marsh birds.

“Researchers predict that rising sea levels and increased flooding events may drive the saltmarsh sparrow, a coastal species in the US, to extinction, possibly even within the next 20 years,” Dr Bailey said.

“Like the Eurasian oystercatcher, this species does not appear to be adapting to the changing tidal conditions.”

A similar study in Europe showed strong declines in coastal bird species along the coast of Northern Europe.

“Our work is part of a growing amount of research that shows the vulnerability of coastal bird species. These species may need additional conservation focus in the future,” he said.

Første danske koloni af den sjældne sølvhejre opdaget

(Jan Skriver 1 June)

Danmarks første koloni af sølvhejre er fundet i fuglereservatet Vejlerne i Nordvestjylland. Fire par af den kridhvide hejre har æg og unger i naboskab med grå fiskehejrer. Sølvhejren ventes at sprede sig som ynglefugl i Danmark i takt med klimaændringerne. De senere år er antallet af observationer af arten vokset eksplosivt i det danske landskab.

Den lysende hvide sølvhejre har fået så solidt fodfæste i den danske natur, at den første koloni af arten er en realitet.

Fire par yngler i naboskab med en snes par fiskehejrer i reservatet Vejlerne i Nordvestjylland. Hejrerne har deres reder ved Torsbjerg nær Skårup Odde i høje nåletræer, hvor de er yderst vanskelige at lokalisere.

Derfor skulle der en droneflyvning til, før fundet af Danmarks første sølvhejre-koloni blev synligt.

– I forbindelse med optællinger af ynglefugle på øer i Limfjorden, tog jeg og Lars Maltha Rasmussen, der er professionel dronefører, en afstikker over Vejlernes hejrekoloni. Jeg havde en mistanke til flere ynglepar af sølvhejre, fordi der ofte sker et fourageringstræk af adskillige hvide hejrer til og fra koloniområdet, fortæller ornitologen Henrik Haaning Nielsen fra Avifauna Consult, der blandt andet udfører naturovervågning i Vejlerne på vegne af DCE, Nationalt Center for Miljø og Energi, Aarhus Universitet samt Aage V. Jensen Naturfond.

– Ganske rigtigt. Da vi fik analyseret dronebillederne på en god computerskærm, kunne vi tælle fire reder af sølvhejre. I den ene rede kunne vi se tre æg. I en anden var der en stor unge. Det er fantastisk, at man via droneoptagelser kan skaffe disse ynglefugledata næsten uden at forstyrre fuglene, siger Henrik Haaning Nielsen.

Danmarks første sikre ynglefund af sølvhejre blev dokumenteret i sommeren 2014, da arten blev fundet ynglende på Saltholm i Øresund.

I 2016 kom Jylland med som yngleområde for sølvhejren, da et par slog sig ned i kolonien af fiskehejrer i Vejlerne. Det enlige par er altså nu blevet til et kollektiv.

Fra sjælden til almindelig

Sølvhejren er en af de fuglearter, der siden 1980’erne har bredt sig mest i den danske natur. For tre-fire årtier siden var arten en sjælden gæst fra lande øst og syd for Danmark, og den blev i reglen kun observeret få gange om året i det danske landskab.

Det er markant anderledes nu om dage. Blandt andet Rømødæmningen, Tryggelev Nor på Langeland og Bremsbøl Sø ved den dansk-tyske grænse tiltrækker i perioder tocifrede antal af sølvhejrer.

I 2012 blev sølvhejren fundet ynglende i Tyskland, England og Sverige. Det var derfor ventet, at den også ville slå sig ned som ynglefugl i Danmark.


New details on nest preferences of declining sparrow

(Physorg 31 May 2017; Photo J. Winiarski)

Theory says that birds should choose nest sites that minimize their risk of predation, but studies often fail to show a connection between nest site selection and nest survival. Understanding these relationships can be key for managing declining species, and a new study from The Condor: Ornithological Applications explores the nest site preferences of Bachman’s Sparrow, a vulnerable songbird dependent on regularly burned longleaf pine forests in the southeastern U.S.

Jason Winiarski of North Carolina State University and his colleagues monitored a total of 132 Bachman’s Sparrow nests in two regions of North Carolina, the Coastal Plain and the Sandhills, measuring a variety of vegetation characteristics. They found several differences between the two regions in what sparrows looked for in a nest site—in the Coastal Plain, they favored low grass density and greater woody vegetation density, while birds in the Sandhills selected intermediate grass density and greater tree basal area. However, none of these features turned out to be related to nest survival.

According to the researchers, the differences between the two regions are likely due to differences in the available plant communities. Bachman’s Sparrows also could be selecting nest sites that allow easy access to nests or maximize the survival of fledglings once they leave, and these aspects may warrant further investigation. Regardless, Winiarski and his colleagues believe their results show the importance of management that mimics historical fire regimes in longleaf pine ecosystems, in order to maintain the diverse groundcover types used by the birds.

The most challenging part of the study was locating sparrow nests to monitor. “Bachman’s Sparrows are notoriously secretive and don’t easily give up the location of their well-hidden nests,” says Winiarski. “Eventually, we stumbled upon a technique of patiently watching adult sparrows at a distance that allowed the birds to behave normally, while being close enough for us to just barely see where they landed with food or nest material. That let us narrow down where the nest site was to within a few meters, and luck and thorough searching led us the rest of the way.”

“It is really remarkable that the authors were able to track the large number of Bachman’s Sparrow nests that they were able to find. As someone who has searched and searched for nests of this species, it is really hard,” according to Purdue University’s John Dunning, an expert on Bachman’s Sparrow ecology who was not involved with the research. “The study shows how consistent management of vegetation structure through the use of prescribed fire remains the most important management and conservation strategy to support breeding populations of Bachman’s Sparrow.”