Gustoća tijekom gniježđenja, smještaj gnijezda, veličina pologa i dimenzije jaja vrste svraka (Pica pica) na području sjeverozapadne Hrvatske

Between 1997 and 1998 the breeding density, nest sites, clutch size and egg dimensions of the magpie (Pica pica) was investigated in a 7 km2 area in the Krapina river valley. We recorded a high breeding density of 4.79 pairs/km2 (during both years). The nests were situated at a height of 1–16 m above ground (mean = 6.74 m). Magpie nests were found in at least 9 species of bushes and trees. We recorded 3–8 eggs in the first clutch (mean = 5.91 eggs). Egg length averaged 33.43 mm, egg breadth 23.35 mm, egg volume 9.288 cm3, egg shape index 1.433 and egg weight 9.22 g. There were no significant differences in egg dimensions between 1997 and 1998 (length: F = 1.79, p = 0.10; breadth: F = 1.41, p = 0.34; volume: F = 1.27, p = 0.52; shape index: F = 1.10, p = 0.78). The positive correlation between egg volume and egg breadth, egg volume and egg length, egg length and egg shape index as well as between egg length and egg breadth were statistically significant. So was the negative correlation between egg breadth and egg shape index. The correlation coefficient (r) between egg volume and egg shape index was near 0.U razdoblju od 1997. do 1998. godine istraživana je gustoća parova na gniježdenju, smještaj gnijezda, veličina pologa i dimenzije jaja svrake (Pica pica) u nizini rijeke Krapine na površini 7 km2. Zabilježena je visoka gustoća naseljenosti 4.79 para /km2 (prosjek za obje godine). Gnijezda su smještena na visini od 1 do 16 m (prosjek 6.74 m). Gnijezda svraka nađena su na 9 vrsta grmova i drveća. U gnijezdima prvog pologa nalazi se 3–8 jaja (prosjek 5.91 jaja). Prosječna duljina jaja iznosi 33.43 mm, širina 23.35 mm, volumen 9.288 cm3, indeks oblik jaja 1.433 i težina jaja 9.22 g. Između prosječnih dimenzija jaja u gnijezdima 1997. i 1998. godine nema značajnih razlika (duljina F = 1.79, p = 0.10; širina F = 1.41, p = 0.34; volumen F = 1.27, p = 0.52; indeks oblika F = 1.10, p = 0.78). Statistički su značajne pozitivne korelacije između volumena i širine jaja, volumena i dužine jaja, dužine i indeksa oblika jaja duljine i širine jaja i negativna korelacija između širine i indeksa oblika jaja. Između volumena i indeksa oblika jaja koeficijent korelacije (r) je blizu 0