Basic design and components
Our basic video-logger units consist of five main components (Figs 1 and 2; Table 1; Video S1): (i) mini DVR, (ii) battery, (iii) micro-SD card, (iv) microprocessor-controlled timer and (v) integrated VHF radio-tag. All components are commercially available, apart from the custom-built timer board, which we will describe in detail in the next section.
Figure 1. Schematic illustration of a programmable, miniature video-logger for deployment on wild birds, showing an assembled, unpackaged unit (left) as well as the arrangement of all main logger components in an ‘exploded’ (and rotated) view (right). For an animation of this model, see Video S1, and for a photo of a logger packaged for deployment on a wild crow, see Fig. 2b.
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Figure 2. Using video-loggers to study the undisturbed behaviour of wild, free-ranging New Caledonian crows. (a) Schematic illustration of the camera view (blue cone) afforded by a tail-mounted video-logger (red) (reproduced from Fig. 1 in Rutz et al. 2007). (b) A video-logger packaged in black polycaprolactone thermoplastic for deployment on a wild crow (cf. Fig. 1, left). (c) A custom-designed, microprocessor-controlled timer enables sophisticated duty-cycling of video-loggers (cf. Fig. 4); four short sections of enamelled copper wire are soldered to the timer board as they would be in a unit that interfaces a camera board (cf. Fig. 1, right). (d) Attachment of a logger, with a section of rubber balloon, at the base of the two central tail feathers of a crow (the bird's head is pointing to the left, out of view). (e) Shed logger found in the forest by tracking the signals emitted by an integrated very high frequency radio-tag (cf. Fig. 1). (f) Damage (red arrows) to the rubber balloon used for attachment, after logger recovery. (g–i) Sample still images taken from crow-borne video footage (g, handling red berry; h, at nest with two young chicks; i, filming another wing-tagged crow – see bottom-left corner).
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Table 1. Approximate cost (in Pound Sterling, rounded to the nearest pound) and mass (in grams) of individual components required for building a programmable bird-borne video-logger; this list refers to our basic design for wild New Caledonian crows. In addition to logger components, a video-tracking project requires some basic tools for logger assembly (soldering iron and consumables, multimeter, Li-Po charger, butane heat gun, assorted small tools, including forceps and scalpels), programming (computer, PICkit™-2 with USB cable and microprocessor interface) and deployment (rubber balloon sections or tape, superglue), as well as for data analysis (micro-SD card reader, video analysis software)
|Components||Cost (GBP)a||Mass (g)b|
|mini DVRc||70|| 6·20|
|Timer (microprocessor)||14|| 0·66|
|Li-Po batteryd||3|| 4·55|
|4GB micro-SDHC card||6|| 0·26|
|Copper wiring||0|| 0·05|
|Packaging materialse||1|| 0·50|
|VHF radio-tagf||145|| 0·47|
Over the last few years, several companies have independently developed cheap solid-state video cameras for entertainment and sports applications. These devices are easily found on the internet with an online search engine (search terms: ‘mini DVR’, ‘spycam’, etc.). As in the past, we do not wish to endorse particular products, as research applications will vary widely in their technological requirements, and product turnover in consumer electronics is so fast that it is impossible to make lasting recommendations (cf. Bluff & Rutz 2008). This said the exact board configurations do not matter, as long as the camera unit is small, produces video-recordings of sufficient quality (our units record at 640 × 480 pixels and 19·7 frames per second) and has a camera orientation that achieves the desired field of view (it is advantageous if the camera head is not attached to the board directly, but via a flexible cable).
Once the logger has been extracted from its plastic or metal casing, significant further weight savings can be attained by removing any nonessential components. Often substantial parts of the main logger board can be trimmed away, in addition to removing redundant (mini-)USB connectors, SD card holders (cards can be glued into place instead) and/or microphones (if audio is not required). In the interest of animal welfare, units should also be made as light as possible (Wilson & McMahon 2006), even for larger species. In case of our particular loggers, we can reduce the mass from 39·6 g for the factory-supplied unit (without micro-SD card) to 6·2 g for a stripped unit that is ready for further modification (without micro-SD card and battery). Depending on battery configurations and other specifications (see below), the deployment mass of a fully packaged logger varies between 12·3 and 13·6 g (mean ± SEM, 12·91 ± 0·08 g, n = 19 loggers), which is significantly less than our earlier actively transmitting video-tags, which ranged between 13·4 and 15·8 g (14·54 ± 0·21 g, n = 18 tags, Rutz et al. 2007; t-test, t22 = −7·26, P < 0·001; cf. Fig. 3a); for reference, a British two-pound coin weighs 12·0 g. Lighter units can of course be constructed using smaller batteries, but at a penalty to video-recording duration.
Figure 3. The commercial development of small video systems for mass consumer markets drives: (a) the miniaturisation of loggers (deployment mass of loggers used for research on New Caledonian crows), (b) increased logger performance (video footage captured per tag that yielded footage) and (c) the decrease in component costs (for a crow tag). Data shown for 2006/2007 and 2009/2010 are for units deployed by Rutz et al. (2007) (grey symbols, n = 18 actively transmitting video-tags) and in this study (red, n = 19 solid-state video-loggers), respectively; white symbols are for prototypes, and grey lines and question marks indicate future trends. The horizontal grey line in panel (c) shows the approximate cost of a small very high frequency (VHF) radio-tag (145 GBP), which is by far the most expensive component of current and future video-loggers. With regard to prototypes, we have recently started working on two different units: prototype-1, shown in panel (a), attempts to minimise logger size and mass (the logger has a more compact build than the design described in the present study and is marginally lighter at c. 10·92 g, with a 220 mAh battery and micro-SD card but without VHF radio-tag and packaging); prototype-2, shown in panel (c) for the year 2013, attempts to minimise component cost (the video board costs only 3 GBP, including postage; the assembled logger is slightly larger than our current units, at c. 6·5 g without packaging, but offers better recording quality, at 1280 × 960 pixels and 30 frames per second).
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To power the video circuit, we use a single 3·7 V lithium ion polymer (Li-Po) battery (see Bluff & Rutz 2008). With our current logger design, a nominal 220 mAh battery of c. 4·6 g yields c. 70 min of video footage, whilst a 300 mAh battery of c. 4·9 g will generate c. 85 min (for a case study, see below). We replace the factory-fitted battery of our units with a 1-C Li-Po cell without over-discharge controller (Tenergy Corp., Fremont, California, USA), as this allows us to maximise video yield by completely discharging the battery during deployment (which may damage the cell and prevent re-use).
We use standard 4-GB micro-SDHC cards, with class-4 writing speeds to ensure seamless video capture (e.g. SanDisk). The advantage of using SD cards for data storage, rather than nonextractable, board-mounted flash memory, is that they are hard-wearing and straightforward to remove from loggers that have been physically damaged or submerged in water. Micro-SD cards are currently available in up to 16 GB, and for most avian video-tracking applications, loggers are likely to be battery – rather than memory – limited. We review remote data download and endless memory options in the 'Discussion' section below.
As with our earlier transmission-based video-tags (Rutz et al. 2007; Bluff & Rutz 2008), our new video-loggers are fitted with a small VHF radio-tag that enables positional tracking of the tagged animal as well as recovery of the shed logger for data download (for further details, see below). PicoPip tags from Biotrack Ltd. (Dorset, UK) are amongst the smallest commercially available radio-tags, and we have found them to be particularly suited for our application. We usually stock a range of tags fitted with Ag379 (0·25 g) and Ag376 (0·40 g) 1·55-V silveroxide batteries, which give c. 5 and 9 weeks of radio transmission, respectively. To save weight, we ask the manufacturer to supply tags with only a thin coating of Plast Dip® (Plasti Dip International, Blaine, Minnesota, USA), but without dental acrylic potting. When packaging units, the VHF radio-tag is positioned at the proximal end of the logger, and its antenna is guided alongside the logger body, projecting distally away from the unit (Fig. 1). We have our VHF tags fitted with light-weight, nonkink alloy antennae. An additional ground-plane antenna (which is shorter than the main antenna and mounted perpendicular to it) can increase VHF tracking range at a minimal weight cost, which could be essential for tag recovery in wide-ranging species or projects in challenging terrain. For systems where birds can be easily re-trapped for logger recovery, and where tracking of tagged birds is impossible or unproductive, such as seabirds that reliably return to their breeding burrows, video-loggers can be deployed without integrated VHF radio-tag, substantially reducing device costs (Table 1; Fig. 3c).
Commercially available video cameras do not provide the programming facilities that are necessary for effective deployment on wild subjects, but they may be suitable, after minimal modification, for work with habituated or trained subjects (Carruthers et al. 2007; Yoda et al. 2011). To maximise the utility of video-loggers as a research tool, scientists need to be able to switch loggers on and off at preprogrammed times. Such ‘duty-cycling’ of units includes the following tasks (Fig. 4): (i) to switch the logger off for an initial habituation period (to allow the bird to recover from trapping/tagging), (ii) to schedule recording to coincide with the species' activity peaks (to increase the likelihood of documenting rare, or interesting, behaviours) and (iii) to record footage in evenly spaced, short recording bouts (to accumulate quantitative, standardised ‘daily-diary’ data).
Figure 4. Schematic illustration of the on–off duty-cycle for a routine video-logger deployment on a wild New Caledonian crow, as implemented by a microprocessor-controlled timer unit (cf. Fig. 2c). Before final packaging, and deployment on a bird, a brief test video (5 s) is shot, to confirm that the logger and timer are working flawlessly and that the camera lens is in focus (if the logger lacks time-stamping, a reference clock is filmed at this stage). For the first 10–48 h, the logger is set to remain on ‘standby’, that is, the camera is not filming; this preserves battery power whilst the bird recovers from trapping/tagging and habituates to the device. On the first morning of video-shooting, several long bouts of 5–20 min each are timed to coincide with the species’ known early-morning activity peak, maximising chances of recording foraging behaviour and social interactions. Subsequently, the logger records ad battery mortem brief bouts of 1–3 min each per hour, enabling quantitative assessment of activity budgets when data are collected for multiple birds. The duration of all recording bouts, and of all interbout intervals, can be programmed individually, and different duty-cycles can be used for different (groups of) birds. The battery of the integrated very high frequency radio-tag lasts for several weeks, so the logger can be recovered once it has dropped off (cf. Fig. 2e). The time axis and the red blocks indicating bouts of video-recording are not drawn to scale and not all recordings of an actual deployment are shown.
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We have developed a microprocessor-controlled ‘timer unit’ that is capable of achieving these functions (Fig. 2c; hardware was designed and built by Ron Joyce, in collaboration with C.R.). Our timer enables us to ‘take control’ of a wide range of commercial camera systems, by simulating the manual button presses that would normally be used to operate units. It works with cameras that have a ‘standby’ function and require two button presses to start recording, as well as with simpler configurations that involve the operation of only one button. Electronically, the timer uses a PIC10F206 RISC microprocessor (Microchip Technology Inc., Chandler, Arizona, USA); a P-channel FET switches the battery power to the camera, and an open collector NPN transistor simulates the button pushes that initiate and end video-recording. To minimise weight, surface-mount components are used on a 0·8-mm PCB. Assembled boards can be sealed with a thin layer of protective coating for applications where physical damage is likely.
Being an 8-bit processor, and for simplicity of software design, the maximum length of any timing interval is limited to 255 units. All key parameters of the duty-cycle can be programmed (within certain bounds) individually for each logger (for details, see Fig. 4). Sleep and recording bouts can be programmed, so that the video-logger either shuts down before the battery is permanently damaged, or alternatively, operates ad battery mortem (see above). The booting-up of loggers takes c. 10–20 s; if video-loggers lack time-stamping capabilities (as is the case with our current design), this start-up time needs to be taken into account both when scheduling video shoots and when back-calculating times for observed behaviours.
The microprocessor code is written in assembly language (software was written by Ron Joyce, in collaboration with C.R.), which reduces space requirements and allows for maximisation of sleep/recording periods. MPLAB® IDE v8.43 compiler (Microchip Technology Inc.) is used to assemble the code and program the microprocessor. Each logger can be programmed with a unique duty-cycle, affording maximum flexibility in terms of tailoring units to specific study objectives or logistical constraints. The timing periods are held in an ‘include’ file that is incorporated into the code when the compiler is run; this means that the timing information can be configured using a simple text editor (such as Notepad; Microsoft, Redmond, Washington, USA), reducing the risk of introducing erroneous source code changes. The timer's firmware and timing periods are programmed in the field using the microprocessor's in-circuit programming capability. We use a PICkit™-2 programmer (Microchip Technology Inc.) that connects to a computer with a standard mini-USB–USB cable and to the timer through a five-pin custom-built interface.
Packaging of loggers
As video-loggers are currently battery limited, their data yield is best maximised using the highest capacity (largest) battery permissible for a final target logger mass (see above), whilst minimising the weight of all other components. Substantial weight savings can be achieved with the packaging of units, and we have spent considerable resources on developing techniques that are superior to our earlier heatshrink-based approach (Bluff & Rutz 2008).
We make thin sheets of packaging material from polycaprolactone thermoplastic (Polymorph; Middlesex University Teaching Resources Ltd., Herts, UK), which are heated gently with a heat gun before being wrapped around and brushed onto the logger unit. This way the casing of a logger consists of a very thin plastic sheet that is extremely light (Table 1), yet has sufficient integrity to protect the unit from damage (Fig. 2b). Our Polymorph packaging makes loggers splash proof and facilitates component recycling through easy reheating and unwrapping. Our study species has a powerful bill, and although some units were damaged by birds during the first few hours post-tagging, we have found our technique to be adequate in the majority of deployments; our attachment technique with rubber balloons (see below) provides an additional layer of protection across the main body of the unit.
We produce thin sheets of Polymorph by heating a single layer of thermoplastic beads in the oven for c. 5 min at 120 °C, then rolling them into a uniform sheet of c. 1·5 mm thickness. This sheet is then drawn across a preheated c. 200 °C hot board of tempered glass to produce even thinner sheets (c. 0·1–0·2 mm thickness). The desired thickness can be achieved by altering the speed at which the sheet is drawn across the hot glass.
Our loggers can be packaged for deployment on diving seabirds, using a combination of heatshrink (for the main body of the logger; material as described in Bluff & Rutz 2008), machined perspex housing (for the camera head) and fish tank silicone sealant (for sealing the heatshrink–perspex interface). A unit that was successfully attached to a Manx shearwater Puffinus puffinus in 2011 had a deployment mass of 16·05 g, recording 34 2-min video bouts over a 2-day period (C. Rutz and T. Guilford, unpublished data).
As with our earlier video-tags, we mount units on the base of the central tail feathers, with the camera head pushed through the feathers and bent forwards to provide an ‘under-belly’ camera view (Fig. 2a; Rutz et al. 2007). This technique positions the unit close to the bird's centre of gravity, provides unobstructed camera view during foraging (i.e. whenever the bird bends forward, its head appears in view of the camera) and, importantly, enables safe logger release after footage has been captured. Unlike transmitting units, our new video-loggers need to be recovered for data download (Fig. 2e,f), so they must be attached nonpermanently – sufficiently long to enable completion of the scheduled video shoots, but no longer than necessary.
With our loggers, which are optimised for deployment on crows, video shoots are typically completed 2–4 days after tagging, so we developed an attachment technique that would reliably release units after c. 5–10 days (Fig. 4). Generations of field biologists have tried, without much success, to develop reliable and safe release mechanisms for terrestrial wildlife biologging devices. Trialled techniques included weak-link harnesses, glues, surgical thread and even small amounts of explosives. Some of these techniques have been found to put animals at risk because they occasionally result in partial release (e.g. partly opened harnesses can entangle birds; Millspaugh & Marzluff 2001), whilst others have unreliable release timing or are too heavy for smaller species.
After extensive pilot testing, we settled on a very simple and cost-effective design: short sections cut from rubber air balloons. We use so-called rocket balloons (e.g. Henbrandt Ltd., Ipswich, UK), which when deflated have suitable external dimensions (long and narrow) and wall thickness (medium). We prefer cheap makes as they tend to degrade quicker than better-quality balloons, but studies that require longer-term logger attachment may need to opt for more durable materials.
The attachment principle is simple: we insert the activated, packaged logger into a tube of balloon (slightly longer than the logger) that is held open by metal tongs; we then ‘feed’ the bird's two central tail feathers through the balloon tube, to sit underneath the logger, but inside the balloon; once the logger is positioned at the base of the central tail feathers (and is not interfering with the preening gland), the metal tongs are carefully withdrawn – the balloon will contract and ‘clamp’ the logger in place, without the need for any glues (Fig. 2d). A small rectangular piece of polystyrene, glued centrally to the underside of the logger, sits tightly between the two central tail feathers and prevents them from crossing over. Where the camera lens is pushed through the central tail feathers, a few feather barbs may need trimming, so that they do not obstruct camera view; only a few millimetres will need to be cut from a very small number of barbs. The VHF antenna can be attached to the shaft of one of the tail feathers with a few drops of superglue (which prevents it from moving around uncontrollably, which in case of our alloy antennae is noisy), keeping in mind that attachment should be weak enough to break when the main logger unit falls off. Exposed superglue can be set instantaneously with an activator spray (e.g. Loctite 7455 Activator; Loctite, Herts, UK) or simply a drop of water.
Other mounting techniques and camera angles may be preferable for other study species, as we have discussed in detail elsewhere (Bluff & Rutz 2008). For example, in a recent deployment on a shearwater (see above), units were mounted on the back of the bird with a few strips of Tesa® tape (Hamburg, Germany; cf. Guilford et al. 2008).
As our new video-loggers store all video data onboard, fieldworkers do not have to be present during video shoots, substantially simplifying fieldwork logistics in comparison with our earlier transmission-based technology (Rutz et al. 2007; Bluff & Rutz 2008). We still advise, however, that scientists make good use of the loggers' integrated VHF radio-tags and monitor the movements of tagged subjects before, during and after video shoots (Rutz et al. 2007; Bluff & Rutz 2008), as it is the combination of video data and positional (radio-tracking) information that produces particularly rich data sets (Rutz & Bluff 2008). We disagree with the view that the use of bird-borne video cameras is incompatible with productive radio-tracking (Millspaugh et al. 2008). Video-tags/loggers contain powerful VHF radio-tags that enable the collection of many weeks, or even months, of positional data, which is plentiful for conducting conventional home range and habitat use analyses (Rutz & Bluff 2008). In other words, video-loggers offer research opportunities very similar to those of normal VHF radio-tags, but add substantial value by generating precious, complementary video material.
Once on the bird, the logger follows its preprogrammed duty-cycle (Fig. 4). The balloon attachment gradually degrades because of sun (UV) exposure and will develop small holes after a few days (Fig. 2f); these holes release the balloon's tension, allowing the logger to slide off the tail feathers (for more details, see 'Case study'). Detached loggers (Fig. 2e) are easily found using well-established cross-triangulation and search techniques for low-lying, stationary VHF radio-tags (Kenward 2001).