The study is an attempt to describe the formation of the urban heat island in Warsaw on different times of the day on the basis of three observation hours (7, 13, 21 h local time). To obtain this, daily data were used for the period 1961-65 from 5 meteorological stations. As a working material daily air temperature differences were used between urban stations and suburbs (station Warszawa-Okęcie as a relation point). Urban area has usually higher air temperature in relating to its surroundings, however opposite situations are possible: differences between urba stations and suburban ranged from +9ºC to -4ºC. The largest thermal differentiation between the towns on the season of the year. The highest positive differences (the highest intensity of the heat island) between the city and its surroundings related to high weather (small cloudiness, low wind velocity), and opposite istuations are joined with outwardly wind fro the city (north and East – suburban station on the leeward side). Frequency result ΔT ≥ 3.0ºC was evaluated for at least one urban station, and in every observation period. Differences of this kind mostly occur in the evening (21h), for approximately 12.2% days of the year, but their number depends on the weather conditions.
The study was carried out in Central Poland (52°15'N, 19°25'E) by all-day visual observation of five nests of Barn Swallows feeding their nestlings. Feeding frequency of older (age of 14-20 days) nestlings changed significantly with time of the day and was highest (46 visits/h) before noon, declining in the afternoon (21 visits/h) and after a slight increase during the early evening (25 visits/h) declining again in late evening. Feeding frequency of younger (age of 6 days) nestlings did not showed significant changes in the day cycle (average 20 visits/h). The proportion of midday feedings increased with nestling age while the proportion of evening feedings decreased.