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Feather eating in Great Crested Grebes Podiceps cristatus: a unique solution to the problems of debris and gastric parasites in fish‐eating birds

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Abstract

The occurrence of feathers in stomachs of 407 Great Crested Grebes Podiceps cristatus from Lake IJsselmeer, The Netherlands, is described. Only four of the 8718 identified stomach feathers originated from a species other than Great Crested Grebes. In all, 68% were breast and belly feathers and 19% were flank feathers. Flank feathers were positively selected from those becoming available during moult, and also occurred more in the ejected feather pellets than expected from the intake. This suggests that flank feathers, which are long and curved and have a black tip, may be especially suited for the formation of pellets. Feather ingestion was more than balanced by feather production. Feathers were most abundant in stomachs in autumn and were least numerous in winter. Most of this variation can be explained by seasonal differences in the intensity of body moult. In addition, the type of prey was related to the number of ingested feathers. When the diet consisted of smelt, which leave little indigestible matter, more feathers were eaten than with a diet of perch and pikeperch, which leave more fish debris. We suggest the hypothesis that ingested feathers, in the absence of other indigestible matter, contribute substance to the stomach content, enabling the formation of pellets that can be ejected. The habit of regularly ejecting the stomach contents minimizes the chance that any serious population of gastric parasites will build up in the upper part of the alimentary tract.
... Following maceration in their non-acid stomach (pers. obs.), fine material passes the pyloric feather plug-sieve (Piersma & Van Eerden 1989) into the intestines. Hard, bony material, however, stays behind in the stomach, trapped inside a feather ball. ...
... Hard, bony material, however, stays behind in the stomach, trapped inside a feather ball. The stomach-feathers are actively eaten and periodically a pellet is produced, thereby casting out all remains accumulated in the stomach (Piersma & Van Eerden 1989). Remains of the fish, i.e. otoliths and pharyngeal bones, can be used to reconstruct the size and mass of the fish. ...
... The latter argument hinges on the assumption that with a pellet the complete stomach content is evacuated, which seems very likely considering the compact structure of the feather ball (Geiger 1957ejection takes place at fixed intervals, irrespective of stomach content, and justifies the use of average accumulated prey mass as an index for the food intake of a population of grebes. The grebes probably eject a pellet every other day (piersma et al. 1989piersma et al. , Kop 1972, pers. observations on captive grebes), presumably at night or very early in the morning (Simmons 1973, Piersma et al. 1988). ...
... Some species of birds ingest feathers. After ingestion, grebes (Podicipedidae) form a pellet, almost entirely composed of their own moulted feathers (Piersma & Van Eerden, 1989). This was proposed to allow bones and other sharp objects to be insulated (Simmons, 1956), protecting the alimentary tract from puncture. ...
Article
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The ability of feathers to perform many functions either simultaneously or at different times throughout the year or life of a bird is integral to the evolutionary history of birds. Many studies focus on single functions of feathers, but any given feather performs many functions over its lifetime. These functions necessarily interact with each other throughout the evolution and development of birds, so our knowledge of avian evolution is incomplete without understanding the multifunctionality of feathers, and how different functions may act synergistically or antagonistically during natural selection. Here, we review how feather functions interact with avian evolution, with a focus on recent technological and discovery‐based advances. By synthesising research into feather functions over hierarchical scales (pattern, arrangement, macrostructure, microstructure, nanostructure, molecules), we aim to provide a broad context for how the adaptability and multifunctionality of feathers have allowed birds to diversify into an astounding array of environments and life‐history strategies. We suggest that future research into avian evolution involving feather function should consider multiple aspects of a feather, including multiple functions, seasonal wear and renewal, and ecological or mechanical interactions. With this more holistic view, processes such as the evolution of avian coloration and flight can be understood in a broader and more nuanced context.
... The marked change in the composition of S. maccormicki pellets from a predominance of penguin feathers at Potter Cove (King George Island) to mosses at Cierva Point (Antarctic Peninsula) suggests an alternative function of feather ingestion (Santos et al. 2012). The elimination of undigested material in pellets impedes the growth of gastric parasite populations in birds that feed on fishes (Piersma & Van Eerden 1989). ...
Article
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The Antarctic Peninsula has experienced some of the most accelerated warming worldwide, resulting in the retreat of glaciers and creation of new areas for plant development. Information regarding the plant dispersal processes to these new niches is scarce in Antarctica, despite birds being important vectors elsewhere. Many bird pellets (with feed remains such as bones and feathers) are generated annually in Antarctica, which are light and easily transported by the wind and include vegetation that is accidentally or purposely swallowed. The aim of this study was to analyze the presence of plant fragments within skua (Stercorarius/Catharacta spp.) pellets collected from two sampling areas in the Maritime Antarctic: Stinker Point (Elephant Island, 17 samples) and Byers Peninsula (Livingston Island, 60 samples), in the South Shetland Archipelago, during the austral summers of 2018 and 2020. In both study areas, five species of Bryophyta were found that were associated with the pellets and viable in germination tests in a humid chamber. The ingestion of Bryophyta for the skuas contribute to the dispersion of different moss species, including to areas recently exposed by the ice retreat. This is the first demonstration that skua pellets effectively act in the dispersion of Antarctic mosses.
... The unique feather-eating behavior in grebes has already been reported (Hanzák, 1952;Simmons, 1956;Storer, 1969;Piersma and Van Eerden, 1989), but there are still some different explanations for this behavior. It was recorded in the Handbook of the Birds of the World (Del Hoyo et al., 1992) that grebes are used to eating their own feathers and picking up subaqueous feathers. ...
... Feather pecking and cannibalism have also been hypothesized to develop out of feather eating. Feather eating is common in some waterfowl to aid digestion (Piersma & van Eerden, 1989); however, domestic birds cannot break down keratin in the digestive tract and therefore cannot use feathers for this purpose. McKeegan and Savory (1999) found an association between feather eating and feather pecking in layer pullets, but this association was not strong enough to establish a causal link. ...
Research
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https://www.nfacc.ca/resources/codes-of-practice/chickens-turkeys-and breeders/Poultry_SCReport_Nov2013.pdf
Chapter
Birds consume a wide variety of food items that must be digested and absorbed. In this chapter, I provide detailed information about avian diets and the different avian dietary guilds, including insectivores, frugivores, invertivores, granivores, carnivores, scavengers, nectarivores, herbivores, and omnivores. The anatomy and physiology of the avian digestive system are also discussed in detail, with information about the interspecific variation in the anatomy and functions of each component of the digestive system, including bills, the esophagus, two-part stomach, small and large intestine ceca, cloaca, and accessory organs, including the pancreas and liver. Information about the phenotypic plasticity of the avian digestive system and regulation of food intake is also provided.
Preprint
The ability feathers have to perform many functions simultaneously and at different times is integral to the evolutionary history of all birds. Many studies focus on single functions of feathers; but any given feather performs many functions over its lifetime. Here, we review the known functions of feathers and discuss the interactions of these functions with avian evolution. Recent years have seen an increase in research on the evolution and development of feather functions because of an increase in high quality fossils with preserved feathers, new tools for understanding genetic mechanisms of feather development, new tools for measuring and analyzing feather color, availability of phylogenies and phylogenetic comparative methods, and an increase in interest in feather molt. Here, we aim to review how feather functions interact with avian evolution, with a focus on recent technological and discovery-based advances. By synthesizing research into feather functions over hierarchical scales, we aim to provide a broad context for how the adaptability and multifunctionality of feathers have allowed birds to diversify into the astounding array of environments and life-history strategies. Overall, we suggest research into avian evolution that involves feather function in any way should consider all aspects of a feathers’ functionality, including multiple functions, molt patterns, ecological/mechanical interactions, and feather wear over time. With this more holistic view, processes such as the evolution of avian coloration and flight can be understood in a broader and more nuanced context.
Technical Report
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This report from Norwegian Ornithological Society (NOF) makes a summary of the current status for the Slavonian Grebe and is a suggestion for a National Action Plan (NAP) for the species in Norway. The report will constitute the technical basis for the Norwegian directorate for nature management (DN) when publishing a NAP for the species in Norway. The Slavonian Grebe is listed as Endangered in the Norwegian Red List of Threatened species in 2006. In 2007, NOF accomplished a total survey of the breeding population of Slavonian Grebes in Norway that produced an estimate of 750‐850 pairs. The survey concluded that the species has increased both in numbers and geographical distribution during the last 20 years with the exception of some areas in the counties Nordland and Troms. I the areas with reported decrease, the magnitude of the decrease is, however, uncertain. Reported decrease in some areas do not necessarily reflect a real population decline, since the numbers of breeding Slavonian Grebes has increased in other areas in the same counties. The Slavonian Grebe quickly exploits new constructed or restored habitats, and may abandon these after a few years in order to settle in other localities. If the focus on the population development is on a local scale, erroneous conclusions on population decline could easily be made, if new potential breeding localities is not surveyed simultaneously. In Nord‐Trøndelag County the population numbers has been stable during the last 15 years, while the distribution area has increased. In all other counties with Slavonian Grebe populations, there has been an evident increase both in population numbers and distribution area during the last 10‐15 years. This situation especially applies for Finnmark, Sør‐Trøndelag, Hedmark, Oppland and Buskerud counties. The classic breeding localities for the Slavonian Grebe in Norway are nutrient‐rich lowland lakes with seepage from cultivated land. In Oppland County, however, many pairs has established themselves in small ponds in peat bogs or forests without nutrient‐rich seepage from agricultural areas, and in Hedmark County, artificial ponds in the agricultural landscape has frequently been used as breeding ponds for the Slavonian Grebe. The population increase in this county is viewed as a direct response to the increased access to suitable breeding habitats. Slavonian Grebes are vulnerable to competition from fish, and a common denominator for the breeding lakes and ponds is often the absence of big fish. The report suggests the following goal for the NAP: In the long term, the Slavonian Grebe should be distributed with a viable population within the natural distribution area of the species in Norway. The current population numbers estimated at 750‐850 breeding pairs should be kept at least at the same level in the future. In the short term the Slavonian Grebe should be managed as a vulnerable species with special considerations and actions in order to maintain the regional populations. We further suggest the following aims for the NAP: * Establish an annual monitoring system from 2010 onwards, * map the factors that induce the Slavonian Grebes abandonment of certain lakes/ponds. *render important breeding lakes for Slavonian Grebes free from American Mink within 2014, * avoid introduction of fish into important or potentially important breeding lakes and remove introduced fish from some lakes in the period 2010‐2014,*establish and maintain a readiness for implementation of conservation actions when needed. Since the Slavonian Grebe apparently don’t have an unambiguous negative population development, it is difficult to be definite on what conservation actions to implement in a regional scale within the time frame of the NAP (5 years). One important action will be to establish an adequate monitoring system in order to follow the population development on an annual basis. We suggest that the breeding populations should be surveyed on an annual basis in the following monitoring areas: Porsanger, Finnmark County, Balsfjord/Storfjord, Troms County, Bø/Vestvågøy, Nordland County, Norsk Ornitologisk Forening – Rapport 5‐2009 6 Levanger/Stjørdal/Verdal, Nord‐Trøndelag County, Vardal/Snertingdalen/Biri, Oppland County. The next National total survey is suggested accomplished in 2014, seven years after NOF’s first total survey. Actions to remove fish are suggested in former good breeding lakes where it is probable that the Slavonian Grebe has disappeared due to introduction of fish. Furthermore, we suggest a reduction/removal of populations of American Mink in the breeding lakes where this species is recorded, especially in the areas where population decline of Slavonian Grebes has been reported. Net fishing in spring may be a significant mortality factor for Slavonian Grebes that get stuck in the nets and drowns while diving. In order to reduce this mortality factor, public awareness campaigns may help, but in some lakes we suggest a ban on net fishing in spring. An efficient way of creating new breeding habitats for the Slavonian Grebe is to establish artificial ponds in farmland areas. This is suggested as a management action in areas with suspected decrease because former breeding lakes have become unsuitable. Human disturbance may cause the Slavonian Grebe to abandon the nest, or it may result in the eggs being exposed to egg predators. One significant source for repeated human disturbance is recreational activities in the lakes, and it is specially those lakes situated close to aggregation of cottages that are exposed to intense recreational activities. It is unknown where the Norwegian Slavonian Grebes are wintering, and it is therefore important to map particularly sensitive areas for the species in relation to oil spill. The report suggests mapping where the Norwegian breeding birds are wintering, through a satellite telemetry project. In addition, other research activities are suggested, like mapping of basic parameters as nutrient availability, clutch size etc. We suggest that office of the County Governor of Troms is delegated the responsibility of implementing the NAP, and that NOF, who accomplished the first National mapping of Slavonian Grebes in 2007 is responsible for the annual monitoring and future National surveys. The NAP is suggested to be implemented from 2010 onwards, and should be subject for evaluation after the second National survey is accomplished in 2014. The annual budget in the period 2010‐2014 is considered to be approx. 560 000 in the first 4 years, and somewhat higher the last year because of the National survey this year. The internet portal Artsobservasjoner www.artsobservasjoner.no should be used for storing and methodical treatment of the monitoring data for Slavonian Grebes.
Chapter
This chapter presents a detailed guide to hand‐rearing techniques for raising grebes. It provides valuable information on record keeping, appropriate intervention, diet protocol, housing, feeding procedures, and care and stabilization criteria considered throughout the hand‐rearing process. The chapter also presents common medical problems encountered in the grebes and appropriate solutions. In addition, it provides information on the processes involved in preparing the grebes for wild release.
Article
Grebes are unique among birds in ingesting their own feathers. This behavior and the subsequent ejection of feathers as pellets have long puzzled ornithologists, who have tended to treat feather-eating and pellet-casting as independent behaviors rather than as complementary components of the digestive process. The diet of many grebes, including those with the most ancestral traits, is dominated by small invertebrates whose exoskeletons are resistant to digestion. Most birds eat grit to mechanically break down hard foods. Not so with grebes, which are chemical digesters. Feather-eating performs two main functions. The first is to retain food until it is fully digested; this is accomplished by a large feather bolus in the gizzard. The second, provided by a distinct group of feathers in the pyloric pouch, is to filter undigested or indigestible items from entering the intestine. Some of the gizzard bolus is probably regurgitated nightly, but the process is incomplete and undigested food can persist in the gizzard overnight and indigestible hard parts for several months. The pyloric plug is expelled irregularly. Inasmuch as feathers and other debris must eventually be discarded, pellet-casting is an inevitable consequence, not cause, of feather-eating. I propose that grebes originated as surface feeders and adopted feather-eating to enhance the efficiency of feeding on small arthropods or other hard-bodied taxa that are difficult to digest. This interpretation is relevant to understand the early evolution of grebes.
Article
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Of 47 food items eaten on the surface by adult Podiceps cristatus australis 55.5% were fish, 31.9% were insects and 12.6% were plants. Chicks in their first week ate mainly fish <55 mm long. Dives lasted on average 20-30 seconds. Feeding success of adults was high while they were feeding chicks. The New Zealand and European subspecies are compared. Differences suggest that much less food is available in New Zealand, which may affect productivity and population size.-from AuthorsPodiceps cristatus australis New Zealand
Article
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A sample of 1450 Great Crested Grebes from the non-breeding season (August–March) which had accidentally drowned in fishing nets in Lake IJsselmeer, The Netherlands, was examined for age and sex differences in linear measurements, body mass, plumage, leg colour and gonad condition. During skinning and drying, wings of non-moulting birds decreased 2.41 mm in length, and wings of wing-moulting birds significantly more: 4.72 mm. The shrinkage is due to changes in the feather follicles and wing elements and not to changes in the actual feather length. Measurements of body, wing, bill, tarsus and keel lengths showed that males are larger than females. The sexual dimorphism is most pronounced in bill length (11 % difference). Differences between juvenile (first winter) and adult birds are small or non-existent. A discriminant function incorporating wing and bill length (age groups lumped), correctly classified the sex of 89 % of the original sample, and 85 % of an independent sample of starved beached birds. The presence (in juveniles) or absence (in adults) of brown lesser upper wing-coverts is a reliable ageing criterion during the whole non-breeding season: only 2 % juvenile females are misidentified. The striped head plumage of juveniles disappears during winter, but there is a large variation between individuals. Adults tend to have one or more greater upper wing-coverts with white inner vanes. Adults often have a wider white stripe between eye and crest than juveniles. Adult males in summer plumage have longer crests and tippets than females. The colour and barring patterns of the inner tarsi vary greatly. Adults generally have a higher density of black bars than juveniles. Adult males appear to have two peaks in testis size: one in spring and a second one in autumn. The grebes weigh least during the wing moult period in August–September. Average body masses of all age and sex groups increase from September to November and then remain essentially stable until April. This pattern is very different from the peaked body mass pattern, described for dabbling ducks and waders wintering at the same latitudes, but resembles the body mass patterns of two sawbill species which also feed on fish in Lake IJsselmeer.1450 in Fischernetzen im IJsselmeer/Niederlande auerhalb der Brutzeit (August bis Mrz) ertrunkenen Haubentaucher wurden auf Alters- und Geschlechtsunterschiede in linearen Krpermaen, Gewicht, Gefieder, Beinfarbe und Gonadenzustand untersucht. Whrend des Abhutens und Trocknens schrumpfte die Flgellnge nicht mausernder Vgel um 2,41 mm, die von Vgeln mit Flgelmauser signifikant mehr um 4,72 mm. Die Verkrzungen konnten auf Vernderungen der Federfollikel und des Flgelkrpers zurckgefhrt werden; die Federlngen blieben gleich. Die Werte fr Krper-, Flgel-, Schnabel-, Tarsus- und Brustbeinlnge sind bei grer als bei . Der Sexualdimorphismus wird am deutlichsten bei der Schnabellnge (11 % Differenz). Unterschiede zwischen Jungvgeln (1. Winter) und Altvgeln sind klein oder existieren nicht. Eine Diskriminanzfunktion basierend auf Flgel-und Schnabellnge (alle Altersklassen) klassifizierte nach Geschlechtern 89 % der Original-Stichprobe und 85 % einer unabhngigen Stichprobe am Strand gefundener Vgel richtig. Das Vorhandensein (Jungvgel) oder das Fehlen (Altvgel) von braunen kleinen Armdecken ist ein verlliches Alterskriterium whrend der gesamten Nicht-Brutzeit (nur 2 % der jungen fehlbestimmt). Das gestreifte Kopfgefieder der Jungvgel verschwindet whrend des Winters; die individuelle Streuung ist aber gro. Altvgel haben oft eine oder mehrere groe Armdecken mit weien Innenfahnen. Altvgel weisen oft einen breiteren Streifen zwischen Auge und Haube als Jungvgel auf. Ad. im Sommerkleid haben lngere Hauben und Krausen als . Die Farbe und das Muster der Streifung der inneren Tarsi variiert erheblich. Ad. weisen im allgemeinen eine hhere Dichte schwarzer Streifen auf als Jungvgel. Ad. scheinen zwei Maxima der Hodengre aufzuweisen: eines im Frhjahr und eines im Herbst. Die Taucher wiegen am wenigsten whrend der Flgelmauser im August–September. Die mittleren Massen aller Alters- und Geschlechtsklassen steigen von September bis November an und bleiben dann im wesentlichen konstant bis zum April. Dieses Muster unterscheidet sich von dem mit einem Gipfel bei Schwimmenten und Limikolen, die in den gleichen Breiten berwintern, hnelt aber dem Massenmuster zweier Sgerarten, die sich ebenfalls von Fischen im IJsselmeer ernhren.
Article
The dark and light color forms of the Western Grebe (Aechmophorus occidentalis) are defined in this study by bill color. Considerable overlap between the phases was found in all plumage color characteristics except facial patterns. The feathers of the head are molted twice annually, and most facial intermediacy of juvenile and wintering birds disappears as the breeding season approaches. Most body feathers are molted once, except those of the flanks, scapular region, and base of the leg, which appear to be in a state of molt throughout the year. These feathers, especially those of the flanks, are believed to be those ingested regularly by the birds. Some birds molt the remiges with the annual (Prebasic) molt in late summer, but some, possibly birds in their first winter, molt them in midwinter. The measurement data indicate that the dark-phase birds on Clear Lake, California are larger and may be descendents of wintering birds from the north.