Relation between climatic factors, diet and reproductive parameters of Little Terns over a decade

Abstract

We used 10 years of data on clutch size, egg size and diet, and 8 years of data on timing of laying on Little Terns (Sternula albifrons) breeding in Ria Formosa lagoon system, Algarve, Portugal to assess whether diet acts as an important intermediary between climatic conditions and breeding parameters. We used Generalized Linear Models to relate (1) the relative occurrence and size of the main prey species, sand smelts (Atherina spp.), with environmental variables, a large-scale climate variable, the North Atlantic Oscillation (NAO) index, and a local scale variable, the sea-surface temperature (SST), and (2) the respective effects of sand smelts relative occurrence, NAO index and SST on Little Tern breeding parameters. The diet of Little Terns was dominated by sand smelts, with a frequency occurrence of over 60% in all years. The winter SST (February) was negatively associated with the relative occurrence of sand smelts in the diet of Little Terns during the breeding season which, in turn, was positively associated with Little Tern clutch size. Our results suggest that negative NAO conditions in the Atlantic Ocean, often associated with rougher sea conditions (greater vertical mixing, stronger winds and lower SST) were related with earlier breeding, and lower SST in the surroundings of the colony during winterespring favour the abundance of prey fish for Little Terns as well as their reproductive parameters. Climate patterns at both large and local scales are likely to change in the future, which may have important implications for estuarine seabirds in Southern Europe.

Gulls as Indicators of Environmental Changes in the North Atlantic: A Long-Term Study on Berlenga Island, Western Portugal

“…However, direct observed effects on breeding performance may be more challenging to discern. Such shifts in resource availability are consistent across different regions, years, and even during distinct phases of the breeding season [21,37,38], and are closely linked to shifts in oceanographic conditions, particularly in relation to NAO values [4,40]. A study conducted on a colony of little terns Sternula albifrons in Ria Formosa, South Portugal, demonstrated that negative NAO values were associated with earlier breeding onset, and lower SSTs during the winter-spring period resulted in increased prey fish abundance, subsequently influencing their reproductive parameters [4].…”

“…Gulls are social seabirds that tend to form extensive colonies during their breeding seasons. Due to their role as opportunistic scavengers and apex predators, often reliant on both human-related activities and marine natural prey, gulls can be used as bioindicators of anthropogenic effects and shifts in the marine environment [1][2][3][4]. By delving into the dietary habits of gulls, the dynamics of marine resource availability can be monitored, which in turn may reflect long-term variations in the environment [5].…”

Changes in Vegetation Cover Explain Shifts of Colony Sites by Little Terns (Sternula albifrons) in Coastal Portugal

“…Monthly data from 1865 to 2013 were downloaded from the National Center for Atmospheric Research website (National Center for Atmospheric Research 2014). Data for the months and years of interest (each April and May from 1976 to 2013) were selected, and the mean April-May NAO index value was computed corresponding to the Little Tern's main laying season (Ramos et al 2013). …”

“…Since the 1970s, breeding population censuses of this species have been carried out in the Algarve in the different colony sites of the barrier islands of the Ria Formosa coastal lagoon system. How ever, local-and large-scale environmental factors affecting foraging conditions and food availability also determine Little Tern breeding parameters (Paiva et al 2006;Ramos et al 2013) and may also influence the number of breeders at each colony site. Thus, we also related the number of breeding pairs with the North Atlantic Oscillation (NAO) index.…”

Identification of adult and juvenileAtherina presbyterCuvier, 1829 in a marine coastal area adjacent to Tagus estuary (NE Atlantic): A molecular tool for an ecological question

“…Along the European coasts there are several morphologically similar fish species that are frequently identified to the genus or family level in regular field campaigns or censuses. Some examples include: Atherina sp., Callionymus sp., Pomatoschistus sp., Trachurus sp., and species belonging to the family Mugilidae (e.g., Azzurro, Pais, Consoli, & Andaloro, ; Félix‐Hackradt, Hackradt, Treviño‐Otón, Pérez‐Ruzafa, & García‐Charton, , ; Horta e Costa et al., ; Ramos, Pedro, Matos, & Paiva, ).…”