Nesting and Incubation Behaviour of the Little Bustard Tetrax tetrax and Its Relation to Hatching Success

In 2010-2016, we monitored 28 clutches of eight adult Little Bustard Tetrax tetrax females tracked by GPS on the Lleida Plain, in the Ebro Depression (NE Spain), to study nesting and incubation behaviour. In addition to describing these behaviours, we used generalised linear mixed models to identify the factors that determine hatching probability, such as laying date, nesting habitat and incubation behaviour. We found a high capacity (53%) to produce replacement clutches following nest failure. Unsuccessful nests represented 67.9% of clutches, mainly due to the low hatching rate of replacement clutches (16.7%) but also of the first clutches (44%). The main causes of failure were nest abandonment or predation (58%), while farming practices were responsible for 38.9% of failures. We found an increased risk of failure due to desertion or predation towards the end of the incubation. The risk of failure was higher in late clutches, although this seemed to be directly related to cereal mowing and to changes in nesting substrate, from cereal to alfalfa, which occurred throughout the breeding season. Likewise, we found a negative effect of the size of the field where the nest was found and of the surrounding habitat on the hatching probability, which we related to the availability of food for the female in these fields. Measures aimed at improving food provision, by increasing field edge density and fallow availability, would help to maintain hens in good condition prior to and during incubation, as well as providing suitable habitat for replacement clutches. Adaptive irrigation and mowing patterns in alfalfa fields during the nesting season could contribute to increasing the hatching success of replacement clutches.—Cusco, F., Bota, G., Llovet, A. & Manosa, S. (2021). Nesting and incubation behaviour of the Little Bustard Tetrax tetrax and its relation to hatching success. Ardeola, 68: 95-122.