Behaviour 2019
The effect of food supplementation on egg production by the Oriental tit and the Varied tit
Jihyun Song1, Injae Hwang1, Jinseok Park1, Jungmoon Ha1, Woojoo Kim1, Keesan Lee1, Sang-im Lee2, Piotr.G Jablonski3. 1Laboratory of Behavioral Ecology and Evolution, Seoul National University, Seoul, , South Korea; 2Laboratory of Integrative Animal Ecology, DGIST, Daegu, , South Korea; 3Museum and Institute of Zoology, Polish Academy of Sciences, Warsaw, , Poland

Avian breeding requires energy to produce eggs, hence food availability before and during egg-laying may affect egg production. To test this idea on the Oriental tit (Parus minor) and the Varied tit (Sittiparus varius), we supplied breeding birds with extra food from nest building to the incubation stage. As the food item, Hermetia illucens larvae were provided in a small plastic container in the corner of a nest box and were replenished every 2-3 days. Based on the first two seasons of study, we found that the total volume of all Varied tit’s eggs in a clutch was significantly larger in food-supplemented than in control nests. No such an effect was observed in the Oriental tit. We hypothesize that the Varied tit may be more sensitive to supplementary food availability because it may be more restricted by available resources. Consistent with this idea, the Varied tit produces smaller clutches (median 6 eggs compared to 9 eggs by the Oriental tit) of smaller total volume, and we propose that small amounts of extra food might have had a more noticeable effect on egg production in this species.