Abstract
Changes in the timing of migratory events have been observed recently in many migratory species, most likely in response to climatic change. In the common tern Sterna hirundo we examined such changes in spring arrival date and body mass based on a 19 year individual-based longitudinal data from a transponder marked colony from 1994 - 2012. Although no long-term trend was observed in either trait, strong inter-annual and age-specific variation in arrival date and mass was evident. We investigated whether environmental factors such as (i) global climate phenomena North Atlantic and Southern Oscillation Indices NAOI and SOI, or (ii) local factors, such as food abundance in the wintering and breeding area, represented by fish stock or marine primary productivity, could explain this variation. We found that 2-year-old birds on their first spring migration advanced arrival relative to spring NAOI and delayed arrival relative to sprat Sprattus sprattus abundance. The arrival date of 3-year-olds also advanced in relation to NAOI and delayed in relation to winter SOI. In contrast, adults delayed arrival with NAOI and advanced relative to SOI. Within age groups, earlier annual arrival coincided with higher mass, indicating that a fast and/or early migration did not come at a cost to body condition. Changes in arrival mass relative to environmental covariates were found only in 2-year-olds on their first spring migration: in these birds arrival mass was positively related to herring Clupea harengus and sprat abundance in the breeding area as well as spring NAOI and negatively related to SOI. In conclusion, traits related to migration of common terns were linked with environmental conditions, but showed no long-term trends over the past two decades. Age-related differences were marked, suggesting that common terns might be subject to differing environmental constraints or respond differently to conditions during their annual cycle depending on age.
Highlights
Physical condition and timing of arrival in the breeding area are important parameters for migratory species with a relatively short reproductive season
Any relationships between arrival date, arrival mass and environmental factors found in this study are not necessarily causal and since we considered only a subsection of possible environmental covariates, there might be other relevant factors not included here
Accounting for the cross-classified random effects of year and bird-ID, when testing for year, age- and sexeffects on arrival date there was a significant difference between age groups (2 year: reference; 3 year: estimate = −31.581; SE = 0.658; adults: estimate = −60.201; SE = 0.495; χ2 = 15782.214; p < 0.001) and between sexes, but the model confirmed the absence of a time trend
Summary
Physical condition and timing of arrival in the breeding area are important parameters for migratory species with a relatively short reproductive season. Arrival date and mass are influenced by, among other factors, environmental conditions during migration and in the wintering area (e.g., Hüppop and Hüppop, 2003; Crick, 2004; Visser and Both, 2005; Parmesan, 2006; Newton, 2008). Environmental conditions can affect traits such as arrival date and mass after migration and cause inter-annual variation in reproductive performance and survival probability. Based on an understanding of inter-annual variation in the timing of arrival and of the birds’ condition upon arrival at the breeding sites, these traits can be used as indicators of changing environments at wintering sites or on migration routes and as a tool for monitoring population health
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
