The use of tracking devices (tags) to investigate seabird movements and habitat use has grown rapidly over the last 30 years, but often tracking data are reported without assessment of the effects of tags. The extra mass and bulk may risk altering behavior, and effects likely vary depending on the size, anatomy, and foraging strategy of different species. A guideline that tags should not exceed 3% body mass is widely accepted by seabird researchers, but this guideline was developed for albatrosses and petrels. A review of tracking studies showed that alcids are more likely to be affected by tags than other groups. We found some evidence of a negative effect of tags on Parakeet Auklets' (Aethia psittacula; mean mass 266 g, tag 0.8–1.1% of body mass) reproductive success but not return rate or chick growth. Tagged Whiskered Auklets (A. pygmaea; mean mass 112 g, tag 1.8% of body mass) showed minor decreases in chick growth, and a 74% lower adult return rate during 2014–2015, despite no significant difference from control returns in 2013–2014. Our study demonstrated negative effects in alcids of tags well below the 3% guideline, confirming that limits for one group should not be uncritically applied to all seabirds. Mass of tags deployed should be kept to a minimum, but other factors (e.g., wing-loading, flight energetics, foraging strategy) may be equally important. To ensure the biological relevance of collected data, we strongly recommend that inclusion of tag effect experiments be considered essential in the design and approval of tracking studies.