490 
THE WILSON JOURNAL OF ORNITHOLOGY • Vo/. 123. No. 3. September 2011 
homogenous and its quality across the colony did been recorded for some larids, including European 
not show any significant variation. Thus, nesting Herring Gull (hints argentatus) (Parsons 1975i 
in central parts of clusters could possibly offer and Glaucous-winged Gull (L. glaucescens) (Hum 
highest advantages in terms of fitness, as it was and Hum 1976). A positive relationship between 
hkely to provide more efficient protection against egg losses and nearest neighbor distance was 
predators and promote higher breeding success found for Kelp Gull (L donunicanus) (Fordham 
(Velando and Freire 2001). Patchy distribution of 1964) and fledijirig success of the Great Black¬ 
nesting habitat suggested lack of the central- backed Gull (L marinus) was lowest in the high- 
peripheral gradients across the entire colony. In density pairs (Butler and Trivelpiece 1981). These 
fact, neither clutch nor egg size was affected by findings support the hypothesis that there could be 
distance to the colony center. Instead, each nest a trade-off between the need for protection against 
cluster acted as a separate unit, in which central- predators and avoidance of intraspecific aggres- 
periphery gradients of clutch and egg size sion in some colonial larid species (Hunt and Hunt 
occurred. 1976) 
Most studied larid species were found to follow 
the central-periphery model of nest distribution. ACKNOWLEDGMENTS 
Higher reproductive success of pairs breeding in 
the center of colonics has been reported for Black¬ 
headed Gull ( Chroicocephalus ridibundus ) (Pat¬ 
terson 1965), Black-legged Kittiwake (Rissa 
tridactyla) (Coulson 1968a), Ring-billed Gull 
{Larus delawarensis) (Dexheimer and Southern 
1974). and Caspian Tern ( Hydroprogne caspia) 
(Antolos et al. 2006). Spatial patterns within the 
colonies of other larids were more complicated 
and could not be unequivocally assigned to any of 
the suggested theoretical models. For example, 
Common Tern (Sterna hirundo ) breeding success 
was positively correlated with nest density, but 
negatively affected by nearest neighbor distance 
(Becker 1995). 
The highest egg volume of Whiskered Terns 
was in the intermediate nest densities. Lower egg 
volume of pairs breeding in the most densely 
occupied areas suggests highest nest densities are 
not favored by high-quality pairs of Whiskered 
Terns. Nesting in particularly high densities by 
several species of larids was disadvantageous in 
terms of fitness. Negative relationships of repro¬ 
ductive success with nest density were generally 
related to intra-specific aggression. Birds nesting 
in high-density areas are likely to be engaged in 
more bouts of agonistic behavior than individuals 
breeding in more sparse areas of a colony (Butler 
and Trivelpiece 1981). Thus, high-denshy pairs 
are hkely to devote more time to nest defense and 
invest less in the other parental activities such as 
food provisioning. It is also possible that chicks 
raised in high nest density areas under conditions 
of food shortage may easily enter territories of 
and McT by adulls (Hunt 
rarest ^°"" h . ld7 , 5) - '^^d chick .survival 
•he high-dens,ty parts of colonies have 
We thank all participants in the field work, especially 
Przemyslaw Wylcgalu, Anna Piasecka. Patrycja Gogga,and 
Banos/ Lcsner. Mary Megalli gave assistance with English. 
We thank Juan A. Amut and an anonymous referee for 
usclul comments on earlier drafts of the manuscript. 
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