This thesis describes the development, testing and field trials of two new varieties of GPS animal tags. One is a sub 20g tracking device which utilizes the GSM (mobile phone) network for telemetry. It has an RMS error of +/-4.7m and solar-powered versions show potential for almost indefinite deployment lifetimes. The second device is a non-telemetry tag which samples 4ms GPS spectrum snapshots and utilizes new post-processing algorithms to enable lower tag power consumption. It weighs 30 grams and has the potential to collect up to 20,000 samples.All aspects of the tags were developed from the ground up, to reduce tag weight and increase tag sample size. The tag development process includes details of: circuit design, construction methods, firmware development and power management techniques.Two tag packaging and attachment systems were developed, a conventional harness-mounted design and a new feather-mounting system for seabird deployments. Several packaging materials were implemented, with the final field trials utilizing carbon-composite packaging in order to enable light, yet robust enclosures which resulted in weight savings of up to 40%.Characterization and testing of the devices included the evaluation of tag accuracy, analysis of telemetry success rates, measurement and characterisation of device power consumption and formulation of lifetime estimates. Pilot field trials were used to assess the tags’ suitability in the planned field trial locations and their likelihood of success.The tags were successfully deployed on three New Zealand bird species. A field trial of the non-telemetry GPS tag on Northern Royal Albatross resulted in the collection of over 26,000 GPS locations over a 4 month period. Field trials of the GPS/GSM tags on Kaka, Northern Royal Albatross and Pateke resulted in the collection of 742, 6,483 and 1,230 data points, respectively. These GPS/GSM tag field trials recorded GPS and GSM success ratios ranging from 49.6 to 97.3% and 19.5 to 71.4%, respectively.Potential tag modifications are detailed together with suggestions of alternative avenues of investigation which have arisen from the research.