Tag Archives: feeding

Study on blue tits: Smell first, and then beg

(Universitaet Bielefeld 12 May 2017)

Nestling blue tits can discriminate between the smell of other nestlings and adapt their begging behaviour accordingly. This is the outcome of the latest study by Dr. Barbara Caspers and Dr. Peter Korsten from Bielefeld University to be published today on the 12th of May in the journal Functional Ecology.

In this subproject, Dr. Barbara Caspers and Dr. Peter Korsten from Bielefeld University and Marta Rossi from the University of Sussex in Brighton (Great Britain) examined the begging behaviour of seven-day-old blue tit nestlings from a population near the Dutch city of Groningen. ‘Blue tit nestlings beg to obtain food from their parents and may have to compete with as many as ten peers in the nest that are not all necessarily full siblings,’ explains Dr. Peter Korsten. In earlier studies of other songbirds, it was already found that this competition intensifies when nestlings are competing with non-kin. Then nestlings beg even more intensively for food.

In the present study, the research team presented nestlings of blue tits with two different smells: an familiar smell of siblings from their own nest and an unfamiliar smell of unrelated nestlings from another nest. In both experimental situations, the biologists then measured how much the nestlings begged. Results showed that blue tit nestlings beg longer and more intensely after being exposed to the smell of the unfamiliar nestlings compared to the familiar smell of their own nest mates. ‘Up to now, we did not know how songbird nestlings were able to discriminate between the smell of close kin and less related individuals when competing for food from their parents. Our study shows that they may well smell this difference,’ says Caspers.

Science had long assumed that birds cannot smell at all. Behavioural researchers together with Dr. Barbara Caspers at Bielefeld University have already been able to disprove this in earlier studies on zebra finches.

Feeding strategies in competing hummingbird species observed in a small area in Brazil

(Pensoft Publishers; 2 May 2017; Photo: Lucas Lanna)

Being the vertebrates with the highest metabolic rate thanks to their rapid wing flaps, the hummingbirds have evolved various types of feeding behaviour. While the nectar-feeders tend to go for food high in energy, strong competition affects greatly their preferences and behaviour towards either dominance, subordination, a strategy known as trapline and a fourth one named hide-and-wait, conclude the Brazilian scientists Lucas L. Lanna, Cristiano S. de Azevedo, Ricardo M. Claudino, Reisla Oliveira and Yasmine Antonini of Universidade Federal de Ouro Preto. Their conclusions following six months of observations in an Atlantic Forest remnant in southeastern Brazil are published in the open access journal Zoologia.

To test previous assumptions as well as their own hypotheses, the researchers placed artificial bird feeders filled with variable in concentration sugar-water solutions across four separate patches at the core of the forest fragment.

The scientists sought to find out whether the birds would show clear preference for the most sugary food source; whether larger size and heavier weight would guarantee better access to the most nutritious feeders; what strategies would be adopted by each species; and which ones would prove the dominant and most aggressive.

As expected, the scientists concluded that the birds prefer the most sugar-dense solutions. However, when subordinate species, such as the white-throated hummingbird and the versicoloured emerald, confronted dominant species guarding the most nutritious food sources, they would be either frightened or expelled following a short chase. Subsequently, these hummingbirds would resort to the feeders with low-sugar solutions.

In their turn, the Brazilian ruby and the violet-capped woodnymph proved to be the dominant and most aggressive species in the studied area. Upon seeing an ‘intruder’ in their territory, which might be either another species, or belonging to their own, they would vocalise their threats, alert them by perching by the feeder, or expel them following a short pursuit. However, they would only try to limit the access for subordinate hummingbirds if the energy that could be gained from the feeder exceeded the energy loss of the chase.

Contrary to another initial hypothesis, it was not the largest and heaviest species that were the dominant ones. There were two species of hermit hummingbirds which were the largest and the heaviest, however, they expressed no territorial or aggressive behaviour. Instead, they were recorded intruding in the territory of the two dominant hummingbird species. In their turn, the Brazilian ruby and the violet-capped woodnymph would often frighten them. Nevertheless, rather than fleeing, the ‘castaways’ were seen hiding in the shrubs, remaining quiet, and returning to the feeder as soon as the dominant bird was gone. This behaviour strategy, named hide-and-wait, has not been reported in hermit hummingbirds prior to this study, according to the authors.

Having reported all feeding strategies in their study, the scientists conclude that the dominant territorial species and the trapliners feed most frequently and most sufficiently, as they use the most sugary sources.

However, the authors note that the high abundance of food, as well as the presence of aggressive territorial species might have affected the hummingbirds’ behaviour and preferences.

In times of plenty, penguin parents keep feeding their grown offspring

Juvenile Galapagos penguin being fed by an adult.

(Author: James Urton; Photo: Godfrey Merlen; March 14, 2017)

Humans are not alone in continuing to support offspring who have “left the nest.” It happens in Galapagos penguins, too.

In a paper published online March 13 in The Wilson Journal of Ornithology, a research team led by University of Washington biology professor Dee Boersma reports that fully grown Galapagos penguins who have fledged — or left the nest — continue to beg their parents for food. And sometimes, probably when the bounty of the sea is plentiful, parents oblige and feed their adult offspring.

“Through field seasons over the years when we were observing penguin behavior in the Galapagos Islands, we saw these isolated instances of adults feeding individuals who had obviously fledged and left the nest,” said Boersma. “And now we’ve collected enough field observations to say that post-fledging parental care is a normal — though probably rare — part of Galapagos penguin behavior.”

In many seabird species, parents continue to feed their offspring after fledging, at least for a limited period of time. But this is not true for the world’s 18 penguin species. Galapagos penguins are now only the second penguin species — after Gentoo penguins — to demonstrate post-fledging parental care. And Boersma does not expect to find more. This behavior in Galapagos penguins, a species she has studied for more than four decades, may be an adaptation to the constantly fluctuating availability of food in the archipelago they call home.

Boersma’s team observed five instances of post-fledging parental care during detailed field observations of wild Galapagos penguins from February 2006 to July 2015. Newly fledged adults — called fledglings — are about 60 days old and sport a distinct appearance due to their lightly colored feet and cheeks, as well as a relatively new and spotless coat of adult plumage.

The researchers saw fledglings on the beach beg for food — using distinctive vocalizations — as adults emerged from the water after feeding. Some adults, presumably unrelated to the fledgling, would peck at the fledgling or move away. But the scientists also witnessed scenes in which a fledgling approached an adult, begged and received regurgitated food from the compliant adult.

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Birds follow green spaces to move between feeders

(Daniel T. C. Cox, Richard Inger, Steven Hancock, Karen Anderson,
Kevin J. Gaston, 23 November 2016 ,Photo Lewis Collard)

 

The benefits of feeding stations are obvious — to the birds that visit them and the people who maintain them — but many gardens are small and separated from other yards by roads, rivers, and other barriers. In order to maximize the benefits, we need to understand how birds move between feeders.

Between June 2013 and August 2014, researchers in southern England employed radio-frequency-identification technology to find out. They equipped 452 Blue Tits and Great Tits, relatives of chickadees, with tiny transponders and placed receivers on 51 feeders. Each time a tagged bird visited a feeder, the receiver recorded the date and time as well as the identity of the bird.

The results promise to help planners looking to improve their communities. The researchers write in the journal Scientific Reports that a higher percentage of vegetation cover increased both the likelihood that birds would move between feeders and the frequency of movement. In areas where green space was highly fragmented, birds moved between feeders in vegetated corridors. Large trees and shrubs were especially important to connectivity, write the researchers, while road gaps did not prevent movement between feeders but did decrease the frequency of visits. — Julie Craves

Read the whole study