Are bio-telemetric devices a drag? Effects of external tags on the diving behaviour of great cormorants

Abstract

Externally attached remote-sensing devices used to study animals in their environment are a possible source of disturbance, notably in terms of drag, for diving species. The aim of the present study was to assess the possible effect of device-induced drag on the diving performance of great cormorants Phalacrocorax carbo. Based on wind-tunnel measurements, we assessed the effect of device size on drag and derived a formula to predict how drag changes as a function of both swim speed and device cross-sectional area. Tests on captive cormorants indicated that drag had an effect on the energy expenditure (using dynamic body acceleration as a proxy) during the dive. Wind tunnel-derived drag metrics were combined with data from the literature to construct a model predicting the power consumption of diving cormorants according to device size. Applying the model to dive data from 6 free-living great cormorants (recorded using implanted time-depth recorders) indicated that a device constituting only ca. 3% of the bird's cross-sectional area could cause a 1.7% increase in power consumption when swimming. However, if a bird maintains constant power underwater, e.g. by decreasing foraging speed with increasing drag, this would result in a 7.1% reduction in the distance travelled during the bottom (active hunting) phase of the dive. Device-related increases in drag are also likely to reduce the maximum speeds achievable by these pursuit predators. The present study highlights the interaction between both drag coefficient and swim speed for diving animals with externally attached devices.

Short-term effects of tagging on activity and movement patterns of Eurasian beavers (Castor fiber)

“…The power required to overcome drag (P) is given by P = 0.5 A Cd v 3 ρ, where A is the cross-sectional area of the animal, Cd is the drag coefficient, ρ is the density of the fluid medium and v is the velocity. Thus, although our attached device would increase the drag by increasing the cross-sectional area marginally, it is the swim speed that is going to be a prime modulator of increased energy expenditure (Vandenabeele et al 2015). Importantly, work by Vandenabeele et al (2015) showed that up to speeds of 1.5 m/s, the energy consumption of a tag-fitted great cormorant Phalacrocorax carbo was unlikely to differ much from the untagged conspecific, but that differences between them accelerated quickly thereafter.…”

“…Thus, although our attached device would increase the drag by increasing the cross-sectional area marginally, it is the swim speed that is going to be a prime modulator of increased energy expenditure (Vandenabeele et al 2015). Importantly, work by Vandenabeele et al (2015) showed that up to speeds of 1.5 m/s, the energy consumption of a tag-fitted great cormorant Phalacrocorax carbo was unlikely to differ much from the untagged conspecific, but that differences between them accelerated quickly thereafter. Thus, since beavers generally swim between 0.8 m/s on the surface (Nolet and Rosell 1994) and 0.6 m/s when submerged (Allers and Culik 1997), we would not expect drag-based power to compromise the animals greatly.…”

“…Until recently, many researchers have considered such effects to be negligible (Wilson and McMahon 2006) with, for example, a review on radio transmitter studies by Godfrey and Bryant (2003) reporting that, of 836 published papers, 83.3 % ignored the impact of marking with tracking devices on their study species. Fortunately, since the early 2000s, awareness of capture and tagging-related effects on animals has grown with researchers using various approaches to tackle potential problems (McMahon et al 2011;Vandenabeele et al 2015;White et al 2013). While some studies found no evidence for such effects (McMahon et al 2008;Ropert-Coudert et al 2009), others showed tagging-related impacts ranging from physiological effects, such as changes in cortisol levels (Cattet et al 2014) or capture myopathy (Höfle et al 2004;Ponjoan et al 2008), to behavioural effects including changes in movement and space use (Morellet et al 2009;Rachlow et al 2014) or generally reduced activity (Broell et al 2016;Dennis and Shah 2012).…”

Effects of added drag on cetaceans : fishing gear entanglement and external tag attachment

“…Tags deployed in capture-release programs (Moore et al, 2016) are typically placed in this preferred position; however, pole-based deployments on cetaceans of any size lead to attachments in any orientation or location. Tags placed on different regions of the body may have considerably different hydrodynamic regimes and will therefore contribute different drag and lift forces and pitching moments: when placed ahead of the point of maximal girth tags can lead to early flow separation and large increases in frontal area , but those placed too far caudally can result in body destabilization (Culik and Wilson, 1991;Healy et al, 2004;Vandenabeele et al, 2015). Suction cup tags such as the DTAG can slide into a new position or orientation as drag forces over the tag exceed suction forces in the cup holding it to the animal (Moore et al, 2016).…”

Neckband or backpack? Differences in tag design and their effects on GPS/accelerometer tracking results in large waterbirds

“…However, this is only one factor to consider during tag development, especially with respect to affecting the behaviour, physiology or demography of the animal [20,21]. Tag weight has received a lot of attention, especially in flying or diving animals [40,41]. It is generally agreed that tag weight should be <5 % (or <3 % as recently proposed) of the body weight of the animal [42][43][44].…”