Auk’s Top Cited, #10: The Socioecology of Monk Parrots

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FIGURE 1. Monk Parakeet flocks (A) in flight and (B) perched. Photo credit: Steve Baldwin

Over the next few months we are going to be highlighting the most cited papers from our journals in 2014 and 2015, counting down from number ten to number one. We begin this week with The Auk‘s tenth most cited paper from 2014-15: The socioecology of Monk Parakeets: Insights into parrot social complexity, by E.A. Hobson, M.L. Avery, and T.F. Wright.

Hobson, Avery, and Wright observed both captive Monk Parakeet flocks and wild flocks in Argentina in order to quantify the basic aspects of their social structure and associations, the first detailed account of social structure in any parrot species. They found that pairs were the basic social unit, though these were not always heterosexual breeding pairs, and that fission and fusion of subgroups within flocks was common. Monk Parakeets showed clear dominance hierarchies within flocks and did not share foraging information with each other.

This evaluation of Monk Parakeet socioecology provides methods that can be used to quantitatively understand social structure in other parrots and other social species in general. Some aspects of Monk Parakeet social behavior uncovered by this study are similar to that of corvids, and the authors suggest that the similarities between parrots and other socially complex groups such as corvids and primates make parrots a taxon of potentially great value in the broader study of the costs, benefits, and drivers in the evolution of social complexity.

Read the full paper at http://www.aoucospubs.org/doi/full/10.1642/AUK-14-14.1.

Spotted Eggshells May Indicate Sickly Mothers in Great Tits

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An adult Great Tit. Image credit: M. Laczi.

The many colors and patterns of bird eggs can provide camouflage and help parents tell their own eggs apart from those of invaders, but a forthcoming study in The Auk: Ornithological Advances suggests another function for eggshell patterns—they can provide information about the health of the mother. The researchers behind the new study found that the patterns of reddish-brown spots on the white eggs of Great Tits reflect the quality and health of the mother bird, with sicker, duller mothers laying eggs patterned with darker spots.

Rita Hargitai of Hungary’s Eötvös Loránd University and her colleagues collected data on female birds’ plumage and health and compared this with the amount of pigment in the eggs they laid. Females that laid spottier eggs had higher levels of immune cells called lymphocytes in their blood, which likely indicates they had high levels of parasitic infections. Females with duller feathers also laid eggs with more dark spots. Protoporphyrins, the pigments that create the reddish-brown spots, can act as oxidative agents, and the researchers speculate that females with poor health deposit more of these potentially harmful compounds into their eggshells to expel them from their bodies.

“Great Tits breed in cavities, so it’s unlikely that egg spotting serves as camouflage to conceal the eggs from nest predators,” according to Hargitai. “In addition, this species has no brood parasites that sneak alien eggs into their nests, and the birds do not eject distinct-looking eggs. Therefore, why Great Tit eggs have a spotting pattern on the eggshell is an interesting question.” Male birds could choose to put less effort into raising chicks hatched from darkly spotted eggs, anticipating that they may be less healthy, though it could also be difficult for them to see eggshell patterns inside dark nest boxes.

Hargitai and her colleagues conducted their research in an oak woodland in Hungary, collecting data from 72 nests over the course of their three-year study. After scoring the degree of spotting on each clutch of eggs, they would wait until they hatched and then return to capture the female birds, weighing and measuring them and collecting feather and blood samples.

“This study provides an important contribution to our understanding of the function of eggshell pigmentation and its role in sexual selection,” according to Branislav Igic, an eggshell coloration researcher from the University of Akron. “The next step in testing this hypothesis is of course to experimentally test whether parental behavior is affected by the variation in eggshell pigmentation. In particular, I find the hypothesis that protoporhyrin may have a negative impact on female condition via its pro-oxidative properties intriguing and deserving of further research.”

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Great Tit nest with eggs. Image credit: M. Laczi.

Darker eggshell spotting indicates lower yolk antioxidant level and poorer female quality in the Great Tit is available at http://www.aoucospubs.org/doi/abs/10.1642/AUK-15-128.1.

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology that began in 1884 as the official publication of the American Ornithologists’ Union. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

Moms Handle the House Cleaning in Cooperatively Breeding Carrion Crows

(The Auk: Ornithological Advances, May 13, 2015)—In cooperatively breeding bird species such as the Carrion Crow (Corvus corone corone), the members of a group share the responsibilities of raising a brood of chicks—but that doesn’t mean everyone contributes equally. Instead, it’s the mother Carrion Crows who carry out most of the tasks related to nest sanitation, including preening the chicks and fluffing the inside of the nest, according to a new paper in The Auk: Ornithological Advances. Diana Bolopo of the University of Valladolid and her colleagues filmed the behavior of Carrion Crows at nests and recorded how individuals spent their time, as well as providing supplemental food at some nests to see if that influenced sanitation behavior. They found that neither did all individuals share all tasks equally, nor were some specialists in either feeding or sanitation; rather, females in general and mothers in particular took on a disproportionate amount of sanitation tasks. The authors suggest that breeding females may be acting in their own self-interest, as they spend more time in the nest and are more exposed to germs and parasites in the nest as a result. Read the full paper at http://www.aoucospubs.org/doi/full/10.1642/AUK-14-233.1.

Subspecies Should Be Based on Both Genetics and Appearance

(March 25, 2015, The Auk: Ornithological Advances)—What is a “subspecies” and why should anyone be concerned about it? Recent studies have created a lively debate around the status of the California Gnatcatcher (Polioptila californica) and other subspecies of conservation concern, and now Michael Patten of the University of Oklahoma has weighed in with a philosophical commentary in The Auk: Ornithological Advances on how we define what a subspecies is in the first place. While species are defined using reproductive and behavioral criteria, subspecies are based on the concept of morphological distinctness, that is, whether populations differ in size, shape, etc. Unlike different species, different subspecies can interbreed with each other. Patten proposes that “subspecies” should be understood to refer to “heritable geographic variation in phenotype.” This means that, to be considered subspecies, populations must be located in different geographic areas and have genetic adaptations to those areas that manifest themselves in the organisms’ appearance. Genetic analysis to determine whether subspecies is valid cannot focus on arbitrarily chosen genes, but should utilize genes connected to phenotypic differences (that is, differences in appearance). Agreeing on a common definition of what a subspecies is will provide a way forward for researchers who study subspecies and, hopefully, a better way of resolving future disputes. Read the full open-access paper at http://www.aoucospubs.org/doi/full/10.1642/AUK-15-1.1.

Power Lines and Human Settlements Drive Bearded Vultures to Abandon Territories in Southern Africa

(January 28, 2015, The Condor: Ornithological Applications)—A new open-access study published this week in The Condor: Ornithological Applications finds that the leading cause of territory abandonment by Bearded Vultures (Gypaetus barbatus) in southern Africa is human activity, rather than food shortages or climate change. Sonja Krüger, Robert Simmons, and Arjun Amar of the Percy FitzPatrick Institute of African Ornithology created a statistical model to evaluate to what degree each of these three factors contributed to nesting territory abandonment in Lesotho and South Africa over a period of five decades. They found the greatest support for the human activity hypothesis, with the most important variables being the density of power lines and human settlements within a territory. Based on their results, the researchers suggest restricting the construction of new power lines and settlements within 10 kilometers of occupied Bearded Vulture territories, taking measures to mitigate the effects of existing power lines, and increasing law enforcement and education in areas where humans and vultures come into conflict. Read the full open-access paper at http://www.aoucospubs.org/doi/full/10.1650/CONDOR-14-121.1.

Photo credit: S. Krueger

Photo credit: S. Krueger

Improved Survey Methods for Studying the Critically Endangered Grenada Dove

(January 21, 2015, The Condor: Ornithological Applications)—The Grenada Dove (Leptotila wellsi) is a critically endangered bird found only on the island of Grenada. Past surveys of its population have found only 68-91 calling males (or 136-182 individuals, if they were all paired with females)—but is that accurate? For a new open-access study published in The Condor: Ornithological Applications, Frank Rivera-Milán of the U.S. Fish and Wildlife Service and his colleagues visited a systematic grid of points in Grenada Dove habitat, with the goals of improving survey methods and identifying dove association with habitat features. They detected 160 individuals, plus or minus about 30. According to their results, doves were easiest to detect in early morning and late afternoon, and they were more abundant in areas with plenty of food and vegetation cover and less abundant in disturbed areas. The authors recommend that their survey method could be used to assess the dove population’s response to management strategies such as forest restoration and the removal of non-native predators. Read the open-access paper at http://www.aoucospubs.org/doi/full/10.1650/CONDOR-14-131.1.

The Grenada Dove (Leptotila wellsi) has a restricted distribution and small population size.  Photo credit: Greg R. Homel

The Grenada Dove (Leptotila wellsi) has a restricted distribution and small population size. Photo credit: Greg R. Homel

Cattle Ranching Supports Greater Bird Diversity than Soybean Farming in Uruguay

(January 14, 2015, The Condor: Ornithological Applications)—Land used for cattle ranching supports larger and more diverse bird communities than soybean fields in the Uruguayan grassland region, according to a new open-access study published this week in The Condor: Ornithological Applications. Thaiane Weinert da Silva, Graziela Dotta, and Carla Suertegaray Fontana of the Pontifícia Universidade Católica do Rio Grande do Sul (PUCRS) in Brazil spent two years surveying and comparing the birds found on soybean and cattle sites in the grasslands of Uruguay and Brazil. Overall, they found that cattle sites had higher species richness than soybean sites and supported more bird species considered representative of southeastern South American grasslands. However, some bird species of conservation interest, such as the Greater Rhea (Rhea americana), were also found in and adjacent to soybean fields, suggesting that more research is necessary to determine exactly how some birds use mixed agricultural landscapes. The message of this study is that when it comes to supporting bird populations, not all types of agriculture are equivalent, and Weinert da Silva and her colleagues recommend that farmers, conservationists, and government agencies in the region come together to discuss how to balance their differing priorities. The full article is available at http://www.aoucospubs.org/doi/full/10.1650/CONDOR-14-85.1.

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A Sedge Wren, one of the grassland birds observed in the study. Photo credit: G. Dotta