Eggshell thinning of osprey (Pandion haliaetus) breeding in Sweden and its significance for egg breakage and breeding outcome.
In the middle of the 1960s low reproductive rate was found in several osprey (Pandion haliaetus) nests in Sweden. Therefore a project was started to investigate the production and to collect unhatched eggs and shell fragments in different regions of Sweden during 1971-2008. Measurements of osprey eggs from museum collections from 1840 to 1970 were included to study long-term changes in shell thickness. In total, eggshell thickness of whole eggs from 666 clutches and of shell fragments from 693 nests was measured. The thinnest shell fragments were recorded in 1973 (mean for 71 clutches: 0.438 mm), minus 15.0% compared to thickness of unaffected eggs before 1946 (0.515 mm). After 1973, shell thickness increased to reach background levels in 2003 (0.515 mm). Thus, it took 30 years to reach full thickness again. From the start of the decrease it took more than 50 years to reach unaffected conditions. The number of whole eggs remaining intact in the nest throughout incubation was reduced when shell thickness decreased. Great loss of eggs due to breakage seems to occur when the mean shell thickness in the clutch was below 0.40 mm. In 1971-1973, when shell thinning was most pronounced, the average thickness of shell fragments was 0.366 mm in nests with 0 intact eggs (minus 29% compared to the pre-1946 background value); 0.393 mm (minus 24%) in nests with 1 intact egg; 0.431 mm (minus 16%) in nests with 2 intact eggs and 0.450 mm (minus 12%) in nests with 3 intact eggs. Differences in thickness were significant for 1 versus 2 intact eggs, 2 vs. 3 intact eggs and for 0+1 vs. 2+3 intact eggs. Actual data from the period 1971-73 shows a decline in the production of young (4-5 weeks) of some 15% (0.25 young per nest).
Department of Environmental Research and Monitoring, Swedish Museum of Natural History, P.O. Box 50007, SE-104 05 Stockholm, Sweden. Electronic address: tjelvar@odsjo.se.
Tjelvar
T
Odsjö
Kvismare Bird Observatory, c/o Jan Sondell, Rulleuddsvägen 10, SE-178 51 Ekerö, Sweden. Electronic address: jan.sondell@telia.com.
Jan
J
Sondell
D000818:Animals; D001947:Breeding; D004528:Egg Shell / Q000737:chemistry*; D004784:Environmental Monitoring; D004785:Environmental Pollutants; D004787:Environmental Pollution; D046093:Falconiformes / Q000502:physiology*; D005260:Female; D008297:Male; D010063:Ovum / Q000737:chemistry*; D012098:Reproduction; D013548:Sweden
D004785:Environmental Pollutants
Breeding result; Eggshell breakage; Eggshell fragments; Eggshell thickness; Eggshell thinning; Sweden