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Plumage Wettability of the African Darter Anhinga Melanogaster Compared with the Double-Crested Cormorant Phalacrocorax Auritus
Abstract
Rijke, A. M., Jesser, W. A. & Mahoney, S. A. 1989. Plumage wettability of the African Darter Anhinga melanogaster compared with the Double-crested Cormorant Phalacrocarax auritus. Ostrich 60:128-132.Darters emerge from water “dripping wet” but are able to become airborne without delay. Their plumage is, on the whole, three times more wettable than that of cormorants. We investigated the microscopic structure and resistance to water penetration of the body, wing and tail feathers of the African Darter, Anhinga melanogaster.The results show values of the structural parameter (r + d)/r for body feathers in the range of 9 to 12, whereas for rectrices, primaries, secondaries and tertiaries, a range of 2 to 3 was observed, with barbules measuring 2 to 3. Penetration pressures measure zero to 1 cm water head for the body feathers and 6 to 15 cm for the wing and tail feathers. These findings suggest that on submersion, the body feathers wet out entirely but wing and tail feathers resist becoming waterlogged which may reduce buoyancy when stalking prey underwater and permit the darter to take to the air immediately after a dive. The results have been compared with those of similar measurements on cormorant feathers, which underscore the dual nature of the darter plumage in terms of water repellency and resistance to water penetration.
... Hydrostatic head tests measure the pressure needed to force water through a porous structure, or conversely, a structure's ability to resist water penetration. Hydrostatic head tests have been conducted by sandwiching a feather between a syringe and a pressure transducer to measure the pressure at first infiltration of water across the feather (Rijke et al. 1989, Mahaffy 1991, Stephenson and Andrews 1997, Grémillet et al. 2005, Ortega-Jiménez and Álvarez-Borrego 2010). Rijke et al. (1989) stacked feathers to simulate the plumage, demonstrating more pressure is required to penetrate through the feathers as you add more to the stack. ...
... Hydrostatic head tests have been conducted by sandwiching a feather between a syringe and a pressure transducer to measure the pressure at first infiltration of water across the feather (Rijke et al. 1989, Mahaffy 1991, Stephenson and Andrews 1997, Grémillet et al. 2005, Ortega-Jiménez and Álvarez-Borrego 2010). Rijke et al. (1989) stacked feathers to simulate the plumage, demonstrating more pressure is required to penetrate through the feathers as you add more to the stack. Results across these studies suggest resistance to water penetration varies across feather type and species, with a consensus that feathers of aquatic species are better at resisting water penetration. ...
... In this hypothetical mechanism, barbs and barbules create a two-scale hierarchical structure that traps air, increasing the area of the water-air interface, and leading to a stable Cassie-Baxter state (Bormashenko 2012, Srinivasan 2014. The rigidity and interlocking nature of pennaceous barbs and barbules prevent the microstructures from clumping under the forces of surface tension (Moilliet 1963, Rijke et al. 1989). If the structure is compromised, by excessive wetting or structure breakdown, water infiltrates into the feather pores, leading to a Cassie-Wenzel wetting transition and wetting the feather (Srinivasan 2014). ...
Feathers are complex integument structures that provide birds with many functions. They are vital to a bird's survival, fundamental to their visual displays, and responsible for the evolutionary radiation of the avian class. Feathers provide a protective barrier for the body; their water repellency is a key feature. Despite hundreds of years of ornithological research, the available literature on how feathers repel water is both limited and puzzling. Most hypotheses from the early 1900s suggested uropygial gland oil provided feathers with a hydrophobic coating. Subsequent studies showed that the feather's hierarchical structure creates a porous substrate that readily repels water with or without oil. Numerous studies and methods have been published attempting to explain, quantify, and compare the water repellency of feathers. Many overlook the role of barbules and the effect of their variation, which both likely play a crucial part in water repellency. The goal of this paper is to synthesize this research to better understand what has been done, what makes sense, and more importantly, what is missing. Previous reviews on this subject are mostly over 30 years old and did not use modern methods for systematic review. Here, we performed a systematic review to capture all relevant published papers on feather water repellency. We emphasize the crucial role of barbules in feather water repellency and why their morphological variation should not be ignored. We answer the question, what do we really know about the water repellency of feathers?
... As a result, the pressure required to force water through the feather is determined only by the diameter and spacing of the barbs without recourse to the barbules. Noteworthy is that the wettability parameter for barbules is more or less constant for all bird families at about 4.5 and does not vary with the feeding habits of water bird families as it does for barbs (Rijke et al. 1989). ...
... Swimmers are subject to a more or less static equilibrium between the pressure exerted by the weight of the bird and the capability of the outer contour feathers to resist penetration. Once the pressure exceeds this resistance, the underlying layers of feathers will eventually be penetrated as well and will provide no further protection against wetting (Rijke, Jesser and Mahoney 1989). ...
... It is not known if this gradient is large enough to force water through the barbs of a single contour feather or a stack of multiple feathers. The available experimental data, few as they are, seem to suggest that each additional feather layer adds another 50 percent increase to water resistance (Rijke, Jesser and Mahoney 1989). Experiments of this kind, in which water is forced through feathers, may well closely resemble the conditions of birds landing on water. ...
The contour feathers of water birds are well-known to show structural details in their distal one-third that optimally confer water repellency and resistance to water penetration. In this study, these details were further examined to see if they also provide resistance to the impact forces of diving and alighting. To this end, 49 species representing 37 water bird families were grouped into nine foraging niches before measurement of length, diameter, and spacing of their barbs. Twelve land bird species grouped into two foraging niches were included in this study for comparison. These measurements allowed the calculation of the ranges and medians for barb stiffness and vane deflection for each foraging niche. A phylogenetic ANOVA approach was followed to determine if the foraging niches for water and land birds explain differences in feather microstructure while accounting for phylogenetic relationships. There were no significant group aggregations for water or land birds confirming the statistical reliability of the ANOVA approach. Differences between the deflection parameter medians of water and land bird foraging niches proved significant demonstrating an evolutionary distinction between these groups. No such difference was observed for the two land bird foraging niches indicating similarity in feather structure. For the water birds, significance was found among all aquatic niches showing that differences in feather microstructure are associated with respect to differences in aquatic feeding niches. These findings support the notion that evolutionary adaptations of feather traits are significant across bird species and their respective foraging niches. The observed mechanical and morphological variations of feathers are therefore considered adaptations to different habitats and behavioral patterns.
... Feather specimens should be covered with fresh preening oil, not rinsed with an ethanol wash (Bormashenko et al., 2007). When these conditions are met, the correct contact angle is usually found to be within one degree error as observed by multiple authors (Adam & Elliot, 1962;Cassie & Baxter, 1944;Rijke, 1965;Rijke, Jesser, & Mahoney, 1989;Shafrin & Zisman, 1952, 1957. ...
... Presumably, these unusual barbules reduce the area of air-water interface between rami leading to smaller values for (r + d)/r and resulting in lower water repellency as confirmed by experiment. But most families, including the genus Cisticola, have rounded barbules that primarily provide a mechanical function by interlocking the rami, preventing them from separating under water pressure while increasing their own separation in the process (Rijke et al., 1989). ...
... The contact angle θ of water drops on smooth feather surfaces, such as the rachis or on a microscopic slide covered with preening oil, measures about 90°as established by various authors (Cassie & Baxter, 1944;Moilliet, 1963;Rijke et al., 1989). The same value was found for water drops on polyethylene foil (Adam & Elliot, 1962) and this is no coincidence: polyethylene almost exclusively consists of methylene groups (-CH 2 -) which are the predominant chemical component of preening oil (Elder, 1954;Odham & Stenhagen, 1971). ...
Birds of the genus Cisticola occur over most of Southern Africa in varying habitats ranging from low to high altitudes and wet to dry areas causing species to have unique distributions. In order to determine if Cisticolas have evolved species-specific water repellency and resistance to water penetration compatible with their habitats, we have measured the barb diameter and spacing of abdominal, breast and throat feathers of six cisticola species and related the results to mean annual rainfall and altitudes in five different locations. Water repellency was not significantly associated with altitude or maximum mean summer temperatures. However, water repellency increased markedly with annual rainfall in the 550 to 600 mm/year range for abdominal and breast feathers, but not for throat feathers. This increase was evident both among species occurring at multiple sites and among different species occurring at single sites. However, the two species occurring at the wettest sites showed low water repellency, but increased resistance to water penetration. These findings suggest that water repellency and resistance to water penetration are part of the evolutionary forces that shape the microstructure of Cisticola contour feathers. 2018 John Wiley & Sons Ltd.
... Feather specimens should be covered with fresh preening oil, not rinsed with an ethanol wash [18]. When these conditions are met, the correct contact angle is usually found to be within one-degree error as observed by multiple authors [14,17,[20][21][22][23]. These results have shown conclusively that contact angles and therefore water repellencies can be reliably calculated from and represented by the dimensions of the porous surface alone. ...
... The contact angle θ of water drops on smooth feather surfaces, such as the rachis or on a microscopic slide covered with preening oil, measures about 90 o as established by various authors [14,16,23]. The same value was found for water drops on polyethylene foil [20] and this is no coincidence: polyethylene almost exclusively consists of methylene groups (-CH 2 -) which are the predominant chemical component of preening oil [24,25]. ...
The contour feathers of water birds are well-known to show a variety of structural details that serves to optimally confer a wide range of functions such as signaling, thermoregulation, buoyancy, water repellency, resistance to water penetration and resistance to the impact forces of diving, plunging and alighting. In this article we review these structural details and the manner in which they contribute to the specific functions. Some functions are in conflict with one another from which optimal balances have evolved. By assigning water bird families to a number of foraging niches we are able to quantitatively compare their functional differences. A number of new perspectives have followed from these comparisons.
... Feather specimens should be covered with fresh preening oil, not rinsed with an ethanol wash [12]. When these conditions are met, the correct contact angle is usually found to be within one degree error as observed by multiple authors [8,11,[14][15][16][17]. ...
... The contact angle θ of water drops on smooth feather surfaces, such as the rachis or on a microscopic slide covered with preening oil, measures about 90° as established by various authors [8,9,17]. The same value was found for water drops on polyethylene foil [14] and this is no coincidence: polyethylene almost exclusively consists of methylene groups (-CH 2 -) which are the predominant chemical component of preening oil [18,19]. ...
... The anhinga was much more similar to the non-diving dabbling ducks, with a slightly higher capacity for glycolysis. Their unique morphology and fully saturable plumage allows them to be neutrally buoyant in ~ 1 to 4 m of water within seconds (Owre 1967;Casler 1973;Rijke et al. 1989). These physical adaptations, plus their slower than expected metabolism (Hennemann 1985), allow the anhinga to adopt a less energetically taxing forage style (Owre 1967;Casler 1973;Henneman 1985). ...
Air-breathing vertebrates face many physiological challenges while breath-hold diving. In particular, they must endure intermittent periods of declining oxygen (O2) stores, as well as the need to rapidly replenish depleted O2 at the surface prior to their next dive. While many species show adaptive increases in the O2 storage capacity of the blood or muscles, others increase the oxidative capacity of the muscles through changes in mitochondrial arrangement, abundance, or remodeling of key metabolic pathways. Here, we assess the diving phenotypes of two sympatric diving birds: the anhinga (Anhinga anhinga) and the double-crested cormorant (Nannopterum auritum). In each, we measured blood- and muscle-O2 storage capacity, as well as phenotypic characteristics such as muscle fiber composition, capillarity, and mitochondrial arrangement and abundance in the primary flight (pectoralis) and swimming (gastrocnemius) muscles. Finally, we compared the maximal activities of 10 key enzymes in the pectoralis, gastrocnemius, and left ventricle of the heart to assess tissue level oxidative capacity and fuel use. Our results indicate that both species utilize enhanced muscle-O2 stores over blood-O2. This is most apparent in the large difference in available myoglobin in the gastrocnemius between the two species. Oxidative capacity varied significantly between the flight and swimming muscles and between the two species. However, both species showed lower oxidative capacity than expected compared to other diving birds. In particular, the anhinga exhibits a unique diving phenotype with a slightly higher reliance on glycolysis and lower aerobic ATP generation than double-crested cormorants.
... Darters roost in mixed colonies with other water birds, but are solitary feeders. Darters can overlap with cormorants in habitat, but darters are less buoyant (Rijke et al., 1989), feed in shallower waters (Ryan, 2007), and prefer fresher waters and areas with dense mangroves or brushy shorelines (Nelson, 2005). ...
Fossil bird data (community composition and taphonomic profiles) are used here to infer the environmental context of the Oldowan-Acheulean transitional period at Olduvai Gorge, Tanzania. This is the first comprehensive report on the Middle Bed II avifauna and includes fossils excavated by the Olduvai Geochronology and Archaeology Project (OGAP) and recently rediscovered fossils collected by Mary Leakey. Crane, ibis, darter, owl, raptor, crow, and vulture are reported from Bed II for the first time. The presence of these taxa, absent earlier in this Bed, point to a general opening and drying of the landscape with grassland and open woodland expansion. Taxa associated with dense, emergent wetland vegetation, such as dabbling ducks and rails, are uncommon and less diverse than earlier in Bed II. This suggests more mature wetlands with clearer waters. Cormorants continue to be common, but are less diverse. Cormorants and other roosting taxa provide evidence of trees in the area. Compared to lowermost Bed II, the Middle to Upper Bed II landscape is interpreted here as more open and drier (but not necessarily more arid), with matured wetlands, scattered trees, and a greater expansion of grasslands.
Feathers might be best known for the pivotal role they play in powered flight, yet they also serve to create a bird's protective barrier to the external environment. This, in part, includes repelling water and keeping birds dry. We argue feather water repellency is among the most crucial feather functions as many other functions rely on dryness for success. All birds interact with water to some degree, and they all evolved from a terrestrial ancestor, suggesting that the feathers of even the most terrestrial birds should have the basic structures required to keep water from penetrating to a bird's skin. Most feather water repellency studies have focused only on aquatic groups, ignoring its necessity in terrestrial birds. Additionally, most use only one feather type, typically the breast feather, assuming that wettability is the same over the whole surface of the body despite feathers differing structurally rather extensively across the body of a bird. Here, we directly measure feather wettability and multiple aspects of microstructure morphology of different feather types across the body. We focus on one species, the Cooper's hawk ( Accipiter cooperii ), a medium‐sized, terrestrial raptor that has minimal exposure to water. We find that even terrestrial birds have hydrophobic feathers, yet wettability varies across different feather types. We also found correlations between barbule morphology and wettability, suggesting barbules play an important role in how feathers repel water. This study provides a baseline understanding of feather morphological variation across a bird at the most basic need for water repellency.
This book has six chapters presenting a wide variety of global seabird-related issues from India to Svalbard, Norway. It has a detailed history of the use and chemical content of guano. It also presents a comprehensive certification scheme in fisheries for seabird protection in Argentina.
The evolution of the feathering arrangements that comprise the modern avian wing can be tracked using both physical evidence from the known fossil record and by interpreting aerodynamic theory. Evidence from both the fossil record and from living birds suggests that all feathered wings reflect the same basic structural plan. Here we review scenarios for the evolutionary history of the lifting surfaces of the feathered wing, suggesting non-locomotory influences on their early development and building on Pennycuick’s (2008) aerodynamic theories for the eventual development of avian flight.
The water repellency of feathers is determined mainly, but not exclusively, by a structural parameter which can be expressed in terms of diameter and spacing of the barbs and barbules. Effective waterproofing properties result from the optimal balance of structural parameter and resistance to water penetration. Comparison of the structural parameters for water birds with the geological time interval of their earliest fossil record shows a phylogenetic tendency toward optimizing waterprooftng properties with the course of time. Several behavioural patterns are discussed which may have evolved under the selective pressure of the quality of water repellency and resistance to water penetration.
Waterproofin and water repel-lency OWE, 0. T. 1%7. Adaptations for locomotion and feeding in the anhinga and the double crested conno-rant The phylogenetic development of water re llency in water bird feathers. Osrrich suppl
- J L Moilliet
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MOILLIET, J. L. 1963. Waterproofin and water repel-lency. Amsterdam, London, New %ork: Elsevier. OWE, 0. T. 1%7. Adaptations for locomotion and feeding in the anhinga and the double crested conno-rant. Omithol. Monogr. 6: M 3. RIJKE, A. M. 1969. The phylogenetic development of water re llency in water bird feathers. Osrrich suppl. 8: g-76.
Some as cts of the thermal hysiology of Anhingas ( A n K g u anhingay and bouble-crested Cormorants
- Ruke Etal
- Darter Plumage Weitability Ostrich
- S A Mahoney
RUKE ETAL. : DARTER PLUMAGE WEITABILITY OSTRICH 60 MAHONEY, S. A. 1981. Some as cts of the thermal hysiology of Anhingas ( A n K g u anhingay and bouble-crested Cormorants (Phalacrocorux ouritus).
- Rijke A. M.