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Changes in the body mass, chemical composition and energetic value of nestlings of the House Martins Delichon urbica from a rural landscape were analyzed over the 21-day period of nestling development. Body weight at the end of this period fell slightly (to 22 g). The growth rate was relatively low (values of K in the 1988 and 1989 breeding seasons were 0.159 and 0.234 respectively). Water content feu by between 86.8 and 64.5%. Protein content increased from 6.7% to 16.5%. Changes in the water and fat indices, and the relatively high fat content (up to 3.4 g), were connected with the strategy of nestling development. Feeding with food caught in the air dependent on the weather, and for this reason the nestlings had to make use of accumulated reserves of fat from time to time. The energetic value of the dry mass of the body was maintained at a level of about 25 kJ, while the caloric value of 1g of biomass rose slightly until day 11, after which it showed a clear increase to the point of flight from the nest (when it was 9.8 kJ). At this time it was twice as high as that on the first day of life.
In the years 1976-1989 392 nests of D. urbica and 584 nests of H. rustica were collectcd from 54 localitics in 6 Provinces in the north of Poland. The highest mean number of specimens per nest was observed in the nest of D. urbica (28.4) and the lowest in nest of H. Rustica (4.2). The highest percentage of nests of the swallows with Oe. hirundinis was recorded in December and lowest in March. The highest mean number of Oe. hirundinis per nest was in the nest of D. urbica in August and lowest in February, and in the nest of H. rustica - in September and in March respectively.
The dynamics of Fe, Mg, Ca, Zn, Cu, Mn, Co, Cd and Pb were investigated in the nestlings of House Martins Delichon urbica, nesting in a rural landscape. Concentrations of iron rose significantly in nestlings during development in the nest, while levels of magnesium rose until days 10-12, but were decreasing at the end of development. Concentrations of calcium showed no changes besides a fall in the liver in the first days of the lives of the nestlings. Zinc accumulated mainly in the liver. The concentration of copper fell in the initial period, and this element was subsequently accumulated in the liver. Manganese was accumulated initially in the liver and later also in the rest of the body. This was attested to by an increase in concentrations outside the liver in the last week of development in the nest Cobalt was stored in relatively large amounts in the liver (mean 2.3 ppm dw), while it was maintained at a steady and lower level outside the liver (mean 0.65 ppm dw). Mean concentrations of cadmium (1.8-3.8 ppm dw) and lead (over 20 ppm dw) did not change with age, and were relatively high. Absolute amounts of all the studied elements rose with the age of the nestlings.
Research was carried out in the years 1988,1989 and 1992 in a colony of House Martins with around 100 nests situated under a bridge on the river Narew near the town of Białystok. No correlation was found between the mean day temperature or humidity and the number of eggs laid, hatching success and fledging success. Recorded in 1989 - but not in 1988 - was a directly proportional relationship between values for hatching success or fledging success and clutch size. The indexes for the rate of increase (K) amounted to 0.159 in 1988 and 0.234 in 1989. The asymptotes for body mass obtained by nestlings amounted to 25.4 g and 24.9 g respectively. The time interval for the increase in body mass from 10 to 90% of the asymptotic mass was 6.6 days in 1988 and 6.4 days in 1989. Studies carried out in 1988 and 1989 focussed on 59 House Martins hatched from 14 nests in the earlier year and 77 from 20 nests in the later one. The proportions in the two years which died prior to the first flight from the nest was 28.1% in 1988 and 41.5% in 1989. A decline in nestling mortality was noted in 1989 with greater clutch size. 1989 mortality in the first brood was 53.1 %, while that in the second brood was 24.2%.
The nestling development of the studied House Martins lasted 20 days. During the first 5-6 days and the last 4-5 days of the development the concentration of haemoglobin increased, while the size of the total surface area of erythrocytes in 1 mm³ of blood increased respectively, manifesting well-fitting. As a result the amount of the haemoglobin functioning on a unit of red cell's surface remained constant. The number of erythrocytes in 1 mm³ of blood increased so significantly, that even despite simultaneous decrease in their size in the last days of the nestlings' development, it causes the increase in the value of haematocrit. Thus the general mechanism forming the respiratory function of a blood volume unit is the same as in other altricial birds. Between the 5th-6th days and the 15th-16th the values of red blood indices did not change. Such a phenomenon did not occur in other studied passerine birds.
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