Table 1 Advantages and disadvantages of different methods used to measure body temperature of birds and mammals

Thermometry, e.g. rectal, oesophageal

✓

×

×

Quick, low-cost, core temperature measurement

Single point measurement, difficult to make on freely moving animals. Stress responses may influence body temperature

Implanted data loggers

✓

✓

✓

Measurement of internal temperature(s) over many months/years. Can be combined with other sensors, e.g. heart rate

Surgical constraints, most cases require recapture for data recovery. Data logger size limitations

Radio transmitters: Implanted

✓

✓

✓

Measurement of internal temperature(s) that can be remotely recorded

Measurement duration limited by battery power. External receiver or manual data logging system required for continuous recording

Radio transmitters: Skin surface

✓

×

✓

Remote measurement of skin temperature. Easily attached by glue

As above. Skin temperature is influenced by environmental conditions as well as physiological parameters. Signal noise increased by movement. External devices increase drag

Gastrointestinal devices

✓

×

✓

Deployment by feed tube/ingested. Continuous recording of internal temperature. Detection of prey/food intake

May require anaesthesia or sedation. Temperature influenced by ingestion/digestion. Measurement period may be limited by gut passage time. Device size limitations

Non-surgical implants, e.g. rectal, aural, vaginal

✓

×

✓

Internal temperature measurement avoiding surgery

Temporary measurement of body region may constrain biological function and limits measurement duration

Faecal temperature

×

×

×

Non-invasive proxy of rectal temperature

Calibration of rectal temperature with faecal temperature required. Temperature prone to vary with environmental conditions

PIT tags

✓

×

×

Low-cost, minimally invasive, multiple discrete measurements avoiding recapture. Temperature measurement possible throughout life of organism

Non-continuous measurement limited by RFID receiver placement. Reading range restricts measurement to close proximity. Migration of tag in some cases

IR thermography

×

×

✓

Remote, non-invasive, sampling with high spatial and temporal resolution. Thermal video allows temperature measurement of discrete behaviours

Influenced by environmental conditions and may not clearly reflect internal temperature. Continuous recording of thermal video over several hours may be limited by memory. Animal must be within field of view of researcher/camera

IR thermometry

×

×

×

Remote, non-invasive recording of surface temperature. Low cost (cf. IRT)

Spatial resolution limited by increasing measurement area with distance. Typical distances of 1–5 m

Temperature-sensitive paint

✓

×

×

Rapid assessment of temperature range of surface by colour change

Low accuracy and resolution. Toxicity and visual marking may affect health/behaviour/predation risk