Grigorios Papakostas’s research while affiliated with University of Macedonia and other places

The foraging behavior of adult and recently fledged juvenile Squacco Herons (Ardeola ralloides) was studied during the breeding season at the Axios Delta, northern Greece. Adults were more efficient foragers than young birds and they had a 37% higher success per peck rate. The majority of adults captured some large prey items, while most juveniles caught only small prey. A comparison between the two age classes, as well as seasonal trends in adult data, indicated a negative association between prey size and foraging rates. Adult and juvenile foraging behavior did not vary significantly between morning and evening. Herons that moved faster also had higher pecking and capture rates, but a lower success ratio. Moving rate did not appear to be correlated with prey size. Herons moved at a slower rate along the edge of dense reed beds, probably in response to this habitat’s physical structure. Adults caught a greater proportion large prey items in open-water areas than in areas with more vegetation.

We studied the relationships between mercury content of Squacco Heron (Ardeola ralloides) chick body-feathers and nestling age, hatching order (seniors-juniors) and growth parameters, and the date of feather sampling in the Axios Delta, northern Greece, in 1993 (n = 75 chicks) and 1994 (n = 80). Mercury levels were not significantly correlated with chick age in either year of the study. Most of the variability in mercury (90%) was found among broods, attributable to differential prey selection and/or foraging habitat and patch utilization by parents. Within broods, juniors had significantly higher mercury loads than seniors in 1993, but there was no significant difference between the two in 1994. Correlations of nestling weight and linear measurements corrected for chick age and mercury concentrations were never significant and explained small amounts of variability in chick growth. However, linear measurements corrected for age were significantly higher among seniors in 1993, when those nestlings had lower mercury loads than their siblings. Mercury levels were unaffected by the date of feather collection in 1993, but exhibited a significant increase over time in 1994. This can be attributed to a shift towards more highly contaminated habitats and prey types by foraging parents, resulting from seasonal changes in water level and vegetation cover in important foraging habitats. Feather collection from Squacco Heron nestlings late in the breeding season seems to be an appropriate method for biomonitoring mercury pollution in the Axios Delta.

The diet and growth of great cormorant (Phalacrocorax carbo) nestlings were studied in the Axios Delta, Greece in 1993 and 1994. The diet, based on analyses of regurgitations, consisted of fish from 12 families. In both years, the dominant prey were the goby Gobius jozo and mullets (Mugilidae). There were changes in number and wet-biomass prey composition during the study, probably due to the opportunistic foraging behavior of the birds. Most prey occurred in aquatic environments at all salinity levels, consisted mainly of benthic fish, and had no particular economic value. The growth of great cormorant nestlings was analyzed using a modification of the method proposed by Ricklefs and White (1975). Sets of estimated values for all variables studied (tarsus, bill, bill+head, and weight) plotted against age yielded sigmoidal curves. The increase in all growth variables over time was best described by the logistic equation. Body weight and tarsus increased at similar rates, and were faster than those for the bill and the bill+head measurements. The inflection point was reached by the tarsus, bill, bill+head, and weight at 10.0, 15.7, 13.5, and 18.6 days, respectively. The potential adaptive significance of this growth pattern is discussed.

Concentrations of the principal organochlorine insecticides were determined in eggs and freshly dead chicks of the Squacco heron (Ardeola ralloides), Little Egret (Egretta garzetta) and Night Heron (Nycticorax nycticorax), as well as in frogs (Rana sp.), the main heron prey. Material was collected from the wetlands of the Thermaikos Gulf (Macedonia, northern Greece) in 1992 and 1993. Residues of the organochlorine pesticides alpha-BHC, beta-BHC, lindane, 4,4'-DDD, 4,4'-DDE, heptachlor and dieldrin were found in the eggs, chicks and prey of the herons. alpha-BHC, beta-BHC, and lindane had highest concentration in the Night Heron and lowest in the Little Egret. In all samples examined, the bioconcentration factors (BCF) of these compounds had very high values. BCF of pollutants for the eggs of the Squacco Heron were at lower levels than those of its chicks. BCF for frogs were in almost all cases lower than those for the other samples. Biomagnification factor (BMF) for 4,4'-DDE and beta-BHC had the highest values of all other compounds (except in the Night Heron). BMF for the eggs of the Squacco Heron were greater than for its chicks. Variation in the pesticide contents in the different heron species is attributed to different feeding habits; the exception being the occurrence of dieldrin in eggs only and 4,4'-DDE as a remnant of past spraying. Amounts of pesticides detected in this study are too low to affect eggshell thickness in the Squacco Heron or have other effects on the wildlife of the area.

The ornithological importance of the Alyki Kitrous wetland (Macedonia, Greece) is evaluated for five groups of birds of special conservation interest by comparison with existing criteria. Ten raptor species (six protected in the EC) occurred but in small numbers. Herons also occurred in small numbers, but wintering great white egrets Egretta alba and wintering and summering spoon-bills Platalea leucorodia occurred in numbers of international importance. Waterfowl were especially abundant in winter, but Alyki was of international importance only for shelduck Tadorna tadorna, although in the past it had also been important for Eurasian wigeons Anas penelope. Alyki was also nationally important for the most abundant wintering anatid species, and for overall numbers, and has been occasionally important for coots. Waders were most abundant in spring migration: avocets Recurvirostra avosetta (during most of the year) and collared-pratincoles Glareola pratincola (in summer) occurred in internationally important numbers. Of breeding waders the same species were important in numbers both internationally and nationally. The latter category also included black-winged stilts Himantopus himantopus. Larids formed one of the most abundant groups, and Alyki was internationally important for particular breeding species such as Mediterranean gulls Larus melanocephalus and gull-billed terns Gelochelidon nilotica. It was also nationally important for breeding common Sterna hirundo and little S. albifrons terns and wintering and breeding slender-billed gulls Larus genei. The Alyki Kitrous wetland is threatened by illegal building and unscheduled development of the salines in the area. Priority conservation measures are proposed.