Towards a quantitative indicator of feather disruption following the cleansing of oiled birds

Highlights

• Computer-based imaging method developed to quantitatively assess feather coherency.

• Imaging method successfully applied in studying cleansing of oil-soaked feathers and to feather coherency assessment.

• Cleansing feathers magnetically imparts less disruption to feather integrity than detergent methods.

Abstract

A computer-based imaging method for determining feather microstructure coherency following a cleansing treatment, was developed, calibrated and trialled on Mallard Duck (Anas platyrhyhchos) feathers. The feathers were initially contaminated with a light crude oil and then cleansed by either detergent (Deacon 90) treatment or, alternatively, by magnetic particle technology (MPT) using iron powder. The imaging method provides a single quantitative parameter for the coherence of feather microstructure and the results confirm that MPT treatment imparts less disruption to the feather microstructure than detergent treatment. It is proposed that this imaging method can be developed and implemented for the assessment of feather disruption and possibly damage, either for the trialling of different treatment protocols, or as a tool during the rehabilitation process, along with other such indicators, to give a more comprehensive assessment of feather condition than is currently available.

Introduction

Magnetic particle technology (MPT) has demonstrated great utility in a range of discipline areas (Safarikova and Safarik, 2001) and is a convenient and quick means by which oil-soaked wildlife can be cleansed (Orbell et al., 2007). This innovative approach has been investigated and developed for the clean-up of oil-soaked species such as the Mallard Duck (Anas platyrhynchos) and Little Penguin (Eudyptula minor) (Orbell et al., 2004). This technology has the advantage of being portable and enables oil to be removed immediately in the field, upon first encounter, either directly or with the aid of pre-treatment agents in cases where the oil residues are highly weathered and/or persistent (Ngeh et al., 2012).

Two further advantages of MPT technology over detergent-based techniques for oil removal are its high efficiency and its purported ability to invoke less damage to the feather microstructure (Orbell et al., 2007). In relation to exploring the removal efficiency of MPT it has been necessary to develop a quantitative assay (Orbell et al., 1997) that can be used to compare the efficiency of MPT technology with those efficiencies offered by detergent cleansing. To this end, computer-assisted analyses such as those developed for the sequestering (Bigger et al., 2010) and the sequential pick-up (Bigger et al., 2013) of chemical contaminants by MPT have been used to process gravimetric laboratory data to quantitatively and objectively determine the efficiency of oil removal under a variety of conditions.

The quantitative assessment of feather condition as indicated by its coherency, on the other hand, remains an area still to be developed. It has long been recognized that feather condition, as manifested in the ability of feathers to repel water, is a key factor governing the decision as to when to release a rehabilitated bird back into the wild (Ngeh, 2002). Work on the quantitative assessment of feather condition includes early studies that applied a theory of water repellence developed by Cassie and Baxter (1944) for woven fabrics and textiles, to the structure of a feather vane (Rijke, 1968, Rijke, 1970, Rijke et al., 2000). It was proposed that the water repellence of contour feathers is mathematically related to the radius of the feather barb and the half-distance between the axes of the barb (Stephenson, 1997, Stephenson and Andrews, 1997).

Further to these early studies, there appears to be very little available literature on the quantitative assessment of feather condition following, say, cleansing or other rehabilitation treatments. Those that have been reported and that provide a quantitative, or at least semi-quantitative, assessment of feather condition, have been developed to varying extents. For example, the presence of preening oils in feathers has long been recognized as an important factor in enabling the feather to repel water (Elder, 1954, Stettenheim, 1972, Elowson, 1984). Based on this observation, the use of gas chromatography to quantify levels of preening oils and waxes in feathers taken from rehabilitating birds has been explored as a possible method leading to the assessment of feather condition (Murray, 1962, Odham and Stenhagen, 1971). Other studies on the assessment of feather condition include those that report the semi-quantitative assessment of wing feather mite infestations on songbirds (Behnke et al., 1999, Carleton and Proctor, 2010) and the use of infrared thermography to assess laying hen feather coverage (Zhao et al., 2013).

A notable and more recent contribution is the work of O'Hara and Morandin (2010) who developed a barbule amalgamation index that is calculated from measurements made of feather rami taken from micrograph images. This index was used as an indicator of feather condition following exposure to oil sheens. A quantitative assessment such as this can be of significant value in the overall assessment of the condition of a bird such as a Little Penguin and, hence, in determining when to release it from a rehabilitation facility. To date, the standard international practice for deciding on the water repellency of the plumage has been to place the penguin in a pool at various stages in the rehabilitation process, monitor its behaviour and buoyancy, inspect the degree of water penetration into the plumage, and make a subjective assessment accordingly (Stocker, 2000, Department of Primary Industries, 2012). Clearly, to have a high rehabilitation success rate such practice requires a high level of experience and expertise in judging when the bird's plumage is fully water-proof and ready for release.

In view of the need for the further development of quantitative methods for the assessment of feather condition, this paper describes a computer-assisted imaging method that can be used to provide a quantitative indication of feather microstructure coherency following treatment by detergent or other cleansing actions. It is proposed that the coherence of the feather structure is an important factor that should be considered along with other factors such as the levels of preening oils and waxes when considering the water resistance and thermal insulating properties of the feather. As such, the coherence of the feather structure can be explored as an important indicator of feather condition. An indicator such as this may also have potential future use in a range of veterinary and husbandry applications.