Wind differentiates reproduction in the non-expansive Black Tern Chlidonias niger and the expansive White-winged Tern Chlidonias leucopterus

Abstract

Identifying the key factors governing the expansion of a species' range is difficult because of the multiple interactions of environmental and biological factors. Among the biological factors are breeding parameters, which at the edge of a species' range may indicate the traits involved in limiting species distribution. To evaluate whether the hatching success of two sympatric species of terns was dependent on weather parameters, a study was carried out in the valley of the River Bug in eastern Poland. During 2007-2010, nine colonies with 113 clutches of Whitewinged Tern (CHL, an expansive species, new to the region since 1997) and 92 clutches of Black Tern (CHN, a non-expansive species, nesting in stable numbers in this region for many years) were monitored. CHN arrived on average 9 days earlier than CHL. While CHN arrived in east-central Poland earlier and earlier during the 1998-2013 period, no such trend was recorded for CHL. The clutch initiation median in CHL was 8 days later than in CHN. The hatching success of CHL was statistically less than that of CHN (41.6 vs. 69.6%). A general discriminant analysis model showed that successful CHL clutches depended on the maximum daytime wind speed (strong winds can be disastrous for breeding terns), colony identity and clutch initiation date. In the case of CHN, none of these factors had a statistically significant influence on hatching success, although the clutch initiation date was very close to being significant. These results suggest that a species which nested in the same location for a long time in relation to ambient weather conditions has higher hatching success than the one which is in the process of expanding its distribution range.

Differences in nest site characteristics and hatching success in White-winged Tern (Chlidonias leucopterus) and Black Tern (Chlidonias niger)

“…The second weather factor negatively influencing clutches was strong winds and wave action during thunderstorms. They perished while clumps of Water Soldier were being pushed around the oxbow, which caused the birds to abandon their nests (Golawski et al, 2017b). The abandonment of nests by parent birds could have been also elicited by, for example, the presence of researchers nearby (during our surveys birds quickly returned to their nests when we were about 15 m away), but bad weather cannot be ruled out altogether.…”

“…Since all the clutches/broods were monitored from the egg-laying stage, Mayfield's method for estimating nest survival when nests are found at different stages of clutch/brood advancement was not used. In the last two analyses, the clutch initiation date (the first-egg-laying date) was taken to be a covariate, since it can have a considerable influence on the success or failure of a tern clutch (Golawski et al, 2017b). GLMM with logit-link function and binomial error variance was used in each analysis.…”

“…Differences in hatching success were due to the phenology of the weather conditions, i.e. heavy rainfall and strong winds, probably accompanying thunderstorms (Golawski et al, 2017b). Such bad weather was more frequent in June and July, so clutches laid later suffered more as a result.…”

“…Such bad weather was more frequent in June and July, so clutches laid later suffered more as a result. These conditions were not only of great importance to CHL clutches; they were primarily responsible for the differences in breeding success between CHL and CHN, as the latter started breeding on average 9 days earlier than the former, probably because of its earlier return from its wintering grounds (Golawski et al, 2017b). High winds and strengthening wave action caused the Water Soldier in the centres of patches to move considerable distances-as far as 350 m in extreme cases, and then clutch destruction was inevitable.…”

“…CHL is thus forced to nest farther away from the helophyte wall, which is why it suffers greater clutch losses. These greater losses are exacerbated by thunderstorms, which become more frequent and fiercer as the terns' breeding season progresses (Golawski et al, 2017b). It appears to us, moreover, that there are many suitable sites for nesting in the Water Soldier patches in the oxbows that the laterarriving CHLs could occupy.…”