SUMMARY
Under our supervision were on average 450 artificial nesting in different years. Studies were conducted in 2006–2014 in the conditions ofoak forestin national natural park “Homilshanski forests” (Kharkiv region) (49°38' north latitude, 36°18' east longitude), pine forests in National natural park “Hetmansky” (50°22' north latitude, 35°01' east longitude) and broadleaf forest natural boundary Vakalivschyna (Sumyregion) (51°01' north latitude, 34°55' east longitude). We investigated 164 layings of great tits and 38 laying of blue tits. Terms of breeding of birds were determined by the date of laying of the first egg. It was found that tits began to lay eggs at steady transition of the average daily temperature over +4 ºC. Maximum amount of started layings was observed in great tits and blue tits in the conditions of the national natural park “Homilshanski forests” (average size – 12.3 ± 1.50 and 12.8 ± 1.75 eggs, respectively) at +15 ºC, with the size of laying gradually decreasing with higher temperatures. Sizes of full layings in great tits (n = 164) and blue tits (n = 38) inSumyand Kharkiv regions were found. With regard to the great tit, it varies from 5 to 15 eggs being on average 10.8 ±1.93 inthe conditions of NNP “Homilshanski forests”, at natural boundary Vakalivschyna – 9.3 ± 2.33 and at NNP “Hetmansky” – 9.1 ± 2.28, while for blue tits it is equal to 5–15 eggs, i.e. 11.4 ± 2.09 on average in the conditions of NNP “Homilshanski forests”, at natural boundary Vakalivschyna – 9.3 ± 2.81 and at NNP “Hetmansky” – 10.5. Size of laying for great tits and blue tits, which prevails for each territory, has been established. The largest sizes for great tits are: 11-egg laying (10.9%) in the conditions of NNP “Homilshanski forests”, 11-egg laying (12.7%) dominating at the natural boundary Vakalivschyna and 9- and 10-egg laying (by 3.0%) at NNP “Hetmansky”. 12-egg laying (21.0%) was often found in the nests of blue tits in conditions of NNP “Homilshanski forests”, size of laying which would be dominating in blue tits at the natural boudary Vakalivschyna and NNP “Hetmansky” was not found. The largest number of laying by great tits was started at NNP “Homilshanski forests” in the second decade of April (n = 28), at natural boundary Vakalivschyna – in early May (n = 25), while blue tits started laying eggs at NNP “Homilshanski forests” in the third decade of April (n = 17), at natural boundary Vakalivschyna – in the first (n = 2) and second (n = 2) week in May. Overwhelming number of layings were started by great tits and blue tits at NNP “Hetmansky” in the third week of April.