Grzegorz Neubauer

Assortative Mating without Complete Reproductive Isolation in a Zone of Recent Secondary Contact between Herring Gulls (Larus argentatus) and Caspian Gulls (L. cachinnans)

ABSTRACT. The zone of secondary contact between Herring Gulls (Larus argentatus) and Caspian Gulls (L. cachinnans) in central Poland is characterized by high levels of introgreeRzemyscular mars several phenotypic characters, with the exception of bare-parts coloration. These patterns suggest a role for coloration as a premating isolating barrier between these species. We investigated the degree of reproductive isolation in this zone of secondary contact by testing three hypotheses: (1) postmating isolation is weak or absent, (2) a partial premating isolation is present, and (3) orbital-ring color or another closely correlated trait is involved in premating isolation, which explains the signal of disruptive selection previously observed (a lower degree of introgression). We also investigated whether differences in breeding phenology could contribute to premating isolation. We found no evidence of postmating isolation, but premating isolation occurred: heterospecific pairs were significantly scarcer than expected under random mating. This assortative mating is best explained by a combination of divergent breeding phenology and mate choice influenced by orbital-ring color. However, because the differentiation in orbital-ring color between L. argentatus and L. cachinnans is incomplete and their breeding periods overlap, premating isolation is only partial. That a previous study found a high level of genetic introgression between these species suggests that reinforcement can occur only in association with sufficiently strong postmating isolation.

Different trapping schemes and variable disturbance intensity do not affect hatching success of Whiskered Terns Chlidonias hybrida

Capsule In the Whiskered Tern Chlidonias hybrida, hatching success was similar at nests where both parents were caught during the same trapping session and nests where parents were caught on different days. Trapping both mates during the same session may represent an efficient approach to reduce fieldwork effort, but it should be preceded by a pilot study, confirming that it does not affect breeding success.

The Importance of Non-Native Prey, the Zebra Mussel Dreissena polymorpha, for the Declining Greater Scaup Aythya marila: A Case Study at a Key European Staging and Wintering Site.

The European population of Greater Scaup Aythya marila has experienced an alarming, ~60% decline in numbers over the last two decades. The brackish lagoons of the Odra River Estuary (ORE) in the south-western Baltic Sea, represent an important area for the species during the non-breeding season in Europe. The lagoons regularly support over 20 000 Scaup, with peaks exceeding 100 000 (38%–70% of the population wintering in NW Europe and the highest number recorded in April 2011–105 700). In the ORE, Scaup feed almost exclusively on the non-native Zebra Mussel Dreissena polymorpha. This mussel was present in the ORE already in the 19th century and continues to be superabundant. Using the results of 22 Scaup censuses (November to April 2002/2003 to 2013/2014) from the whole ORE (523 km2 of water), we show that Scaup flocks follow areas with the greatest area of occurrence and biomass of the Zebra Mussel, while areas with low mussel densities are ignored. The numbers of Scaup in the ORE are primarily related to the area of Zebra Mussel occurrence on the lagoon’s bottom (km2) in a non-linear fashion. Zebra Mussels were absolutely prevalent (97% of biomass) in the digestive tracts of birds unintentionally by-caught in fishing nets (n = 32). We estimate that Scaup alone consume an average of 5 400 tons of Zebra Mussels annually, which represents 5.6% of the total resources of the mussel in the ORE. Our results provide a clear picture of the strong dependence of the declining, migratory duck species on the non-native mussel, its primary food in the ORE. Our findings are particularly important as they can form the basis for the conservation action plan aimed at saving the north-western European populations of Scaup.

Reproductive Performance and Changes in Relative Species Abundance in a Mixed Colony of Herring and Caspian Gulls, Larus argentatus and Larus cachinnans

Abstract. Following range expansion and colonization, hybridization between Herring and Caspian Gulls, Larus argentatus and L. cachinnans, takes place in central and eastern Europe. To examine how hybrid zone is affected by the abundance dynamics of these species and their reproductive performance, we studied a mixed colony at Włocławek Reservoir, central Poland, for over 7 years, from 2002 to 2009, and included data from the species monitoring from 1990 to 2001. To evaluate the species abundance dynamics and possible mechanisms of reproductive isolation, breeders (n = 226 individual birds) were trapped on nests and colour-ringed; breeding performance was studied in detail for 202 breeding pairs with both mates known. Between 2002 and 2009 the proportion of Caspian Gulls among breeders had strongly increased (from 14% to 42%), whereas the proportion of Herring Gulls had declined (from 70% to 35%). The frequency of hybrids varied a little with no clear trend (mean 20%, range 15–28%). The colony size during that time was approximately stable, with 125–135 breeding pairs. 32 individuals originating from outside the zone, ringed as nestlings in the core range of either species, were recorded as breeders at the study site, documenting dispersal of parental species into the zone. The immigration of the two parental species showed contrasting temporal patterns in the two compared decades, 1990–1999 vs. 2000–2009. The immigration of Herring Gulls as measured by the reencounter probability declined nearly three times, while approximately twofold increase was seen in Caspian Gulls. Birds tended to choose phenotypically similar mates, so that there were fewer heterospecific pairs than expected under random mating. Numbers of homospecific, heterospecific and mixed pairs were similar during 7 years. On average, males of Caspian Gulls were significantly heavier than males of Herring Gulls. Caspian Gull pairs bred on average 7 days earlier than pairs of Herring Gulls. No differences in clutch size, clutch volume or hatching success among pairs of different composition were found, indicating weak postzygotic isolation. Current abundance of species in the hybrid zone is changing dynamically and is primarily driven by the strength of immigration from outside the zone.

Leaving on migration: estimating departure dates of Barn Swallows Hirundo rustica from summer roosts using a capture–mark–recapture approach

Capsule Capture–mark–recapture data can be used to predict departure dates of Barn Swallows Hirundo rustica from summer roosts. Aims To investigate how long Barn Swallows remain at their breeding grounds before migration by estimating departure dates. Methods A capture–mark–recapture approach was applied to an extensive data set (65 303 ringed and 710 recaptured birds) from two summer roosts. Multiple-day constancy models were used to estimate apparent survival, which was subsequently translated to residence time. Results The longest intervals between ringing and recapturing were between 66 and 67 days; estimated mean minimum durations were between 16.3 and 18.5 days. Apparent survival was high over most of the summer, indicating that there is little emigration during this period and was followed by a sharp departure-related decline in late August and September. Expected residence time, derived from apparent survival estimates, declined linearly from about 80 days in early July to less than 10 days in September. Estimated departure dates were highly consistent between years and occurred in late September. Conclusions Barn Swallows stay much longer at post-breeding roost sites than is necessary to build up their fat reserves for migration. We suggest that the birds are likely to derive a number of benefits from such a prolonged stay that are not directly related to preparation for migration; for example, minimizing predation risk by foraging in familiar areas, and gathering information on the quality of future breeding sites.

Reproductive Parameters of Caspian Gull Larus cachinnans Pallas, 1811 in Different Habitats Nearby and Away Fish Ponds

ABSTRACT Reproductive performance of gulls depends on a variety of factors, but food abundance and its availability are among the most important. Clutch and egg sizes in gulls are found to be strongly influenced by food availability, thus better reproductive performance in the colony with greater fish availability (near fish ponds) was expected in that study. We compared the reproductive traits (clutch size, volume of eggs in the full clutch, relative volume of the C-egg (the third egg in gulls clutches) and hatching success) of Caspian Gull Larus cachinnans in five inland colonies in Poland located at a gravel pit, a lake, a river and two dam reservoirs. Differences in the clutch size between sites were found, with the lowest at a lake. We found similar clutch volume in all studied colonies. C-eggs were slightly smaller than A- and B- eggs, in all colonies and all study years, but the relative volume of C-egg in colonies located near fish ponds (<10 km) was significantly greater compared to colonies located far away. This may be explained by high fish availability in fishponds in comparison to other habitats. However hatching success (the ratio of the number of hatched chick to the number of eggs laid) was highest in the colony at the lake. This indicates that both inland habitats a gravel pit and a lake offered good food conditions for large gulls when fish ponds are nearby.

Population-level body condition correlates with productivity in an arctic wader, the dunlin Calidris alpina, during post-breeding migration

Weather and predation constitute the two main factors affecting the breeding success of those Arctic waders whose productivity is highly variable over the years. We tested whether reproductive success is associated with the post-breeding condition of adults, in which in ‘good’ years (with warm weather, plentiful food and low predation pressure) the condition of breeders and their productivity is high. To verify this hypothesis, we used a 10-year dataset comprising 20,792 dunlins Calidris alpina, trapped during migration at a stopover site on the southern Baltic Sea shore. Males were consistently in a slightly worse condition than females, likely due to male-biased parental investment in brood rearing. Annual productivity indices were positively correlated with the respective condition indices of breeders from the Eurasian Arctic, indicating that in ‘good’ years, despite great effort spent on reproduction, breeders leave the breeding grounds in better condition. The pattern did not hold for 1992: productivity was low, but the average condition of adults during migration was the highest noted over the decade. We suggest that the delayed effect of the Mount Pinatubo eruption in the Philippines in 1991, could be responsible for the unexpected high condition of Arctic breeders in 1992. High population-level average condition, coupled with the low productivity could stem from severe weather caused by the volcano eruption a year before and strong predation pressure, which in turn lead to a reduced investment in reproduction. The importance of large-scale episodic phenomena, like this volcano eruption, may blur the statistical associations of wildlife with local environmental drivers.

Song Thrush Turdus philomelos and Hawfinch Coccothraustes coccothraustes Exhibit Non-Random Nest Orientation in Dense Temperate Forest

Abstract. Patterns of bird nest orientation in dense forest interiors are relatively unknown. Using data collected in primeval temperate forests at the Białowieża National Park in Poland, we found that two arboreal nesting species, the Song Thrush Turdus philomelos and the Hawfinch Coccothraustes coccothraustes, located significantly more of their nests in the southern half of tree crowns than in the northern half. Nest orientation also depended on nest height: the higher Song Thrush and Hawfinch nests were in the crowns of trees, the stronger preference both species had for locating their nests toward the south. For the Song Thrush, tree species interacted with the date of clutch initiation to influence patterns of nest orientation: Song Thrushes located more of their nests on the ‘south-facing’ sides of live Norway Spruces Picea abies as the nesting season progressed. Spring temperature during the nest construction period affected Hawfinch nest orientation, with significantly more ‘south-facing’ nests during colder springs. The directional orientation patterns we observed may be viewed as a response of nesting birds to weather conditions during nest site selection and nest construction periods, when exposure to solar radiation could help regulate nest temperatures during cold mornings or days.