Backpack-mounted satellite transmitters do not affect reproductive performance in a migratory bustard

Backpack-mounted satellite transmitters (PTTs) are used extensively in the study of avian habitat use and of the movements and demography of medium- to large-bodied species, but can affect individuals' performance and fitness. Transparent assessment of potential transmitter effects is important for both ethical accountability and confidence in, or adjustment to, life history parameter estimates. We assessed the influence of transmitters on seven reproductive parameters in Asian houbara Chlamydotis macqueenii, comparing 114 nests of 38 females carrying PTTs to 184 nests of untagged birds (non-PTT) over seven breeding seasons (2012-2018) in Uzbekistan. There was no evidence of any influence of PTTs on: lay date (non-PTT x = 91.7 Julian day +/- 12.3 SD; PTT x = 95.1 Julian day +/- 15.7 SD); clutch size (non-PTT x= 3.30 +/- 0.68 SD; PTT x = 3.25 +/- 0.65 SD); mean egg weight at laying (non-PTT x = 66.1 g +/- 5.4 SD; PTT x = 66.4 g +/- 5.4 SD); nest success (non-PTT x = 57.08% +/- 4.3 SE; PTT x = 58.24% +/- 4.5 SE for nests started 2 April); egg hatchability (non-PTT x = 88.3% +/- 2.2 SE; PTT x = 88.3% +/- 2.6 SE); or chick survival to fledging from broods that had at least one surviving chick (non-PTT x = 63.4% +/- 4.2 SE; PTT x = 64.4% +/- 4.7 SE). High nesting propensity (97.3% year(-1) +/- 1.9% SE) of tagged birds indicated minimal PTT effect on breeding probability. These findings show that harness-mounted transmitters can give unbiased measures of demographic parameters of this species, and are relevant to other large-bodied, cursorial, ground-nesting birds of open habitats, particularly other bustards.