Effects of body size, sex, parental care and moult strategies on auk diving behaviour outside the breeding season

Information on seabird foraging behaviour outside the breeding season is currently limited. This knowledge gap is critical as this period is energetically demanding due to post‐fledging parental care, feather moult and changing environmental conditions. Based on species’ body size, post‐fledging parental strategy and primary moult schedule we tested predictions for key aspects of foraging behaviour (Maximum Dive Depth (MDD), Daily Time Submerged (DTS) and Diurnal Dive Activity (DDA)) using dive depth data collected from three seabird species (common guillemot Uria aalge, razorbill Alca torda and Atlantic puffin Fratercula arctica) from the end of the breeding season (July) to mid‐winter (January). We found partial support for predictions associated with body size; guillemots had greater MDD than razorbills but MDD did not differ between razorbills and puffins, despite the former being 35% heavier. In accordance with sexual monomorphism in all three species, MDD did not differ overall between the sexes. However, in guillemots and razorbills there were sex‐specific differences, such that male guillemots made deeper dives than females, and males of both species had higher DTS. In contrast, there were no marked sex differences in dive behaviour of puffins in July and August in accordance with their lack of post‐fledging parental care and variable moult schedule. We found support for the prediction that diving effort would be greater in mid‐winter compared to the period after the breeding season. Despite reduced daylight in mid‐winter, this increase in DTS occurred predominantly during the day and only guillemots appeared to dive nocturnally to any great extent. In comparison to diving behaviour of these species recorded during the breeding season, MDD was shallower and DTS was greater during the non‐breeding period. Such differences in diving behaviour during the post‐breeding period are relevant when identifying potential energetic bottlenecks, known to be key drivers of seabird population dynamics

Quantifying nutrient inputs by gulls to a fluctuating lake, aided by movement ecology methods

Eutrophication of aquatic ecosystems is a global problem with major ecological and economic impacts. In many lakes and reservoirs, guanotrophication occurs when roosting waterbirds import nutrients (nitrogen and phosphorus) from surrounding terrestrial habitats. To date, nutrient loading by waterbirds has been estimated based on censuses in the absence of detailed information on their movements. We quantified nutrient importation by the lesser black-backed gull (Larus fuscus) to Fuente de Piedra (1,350 ha) in Andalusia (south-west Spain), where an average of 36,288 individuals are counted in January. During seven winters from 2010 to 2017, we used movement data from 20 individual gulls tagged with Global Positioning System trackers that foraged in four landfills. Together with monthly bird counts and measurements of total N and P content in faeces and pellet samples, movement data were used to quantify the total external loading effect for different winters. Movement data allowed us to quantify the proportion of time spent in the lake and the time spent at different foraging sites and enabled correction of censuses. According to tracking data, on average 69% of the birds had already left the lake to head for feeding sites when waterbird counts were carried out. Nutrient inputs to the lake depend partly on the proportion of the day that gulls spend there, which was higher in late winters and was reduced when lake depth went below or above 20–35 cm. An estimated average of 10.17 kg N ha−1 year−1 and 2.07 kg P ha−1 year−1 were imported to this closed-basin lake by gulls each winter, with highest values recorded in winter 2016–2017. Gull guano is the most important winter source of nutrients to the lake. Regurgitated pellets have been ignored as a source of nutrients in other guanotrophy studies, but we found them to be a more important source of P than faeces. A movement ecology approach complements traditional censuses and facilitates the study of guanotrophication in multiple ways, including identification of sources of nutrients, correction of censuses, and measuring time spent at roost sites.V.M.V. was supported by a PhD contract from Programa Internacional de Becas La Caixa-Severo Ochoa 2016. Lesser black-backed gull count data and FP water levels were provided by the Programa de Emergencias, Control Epidemiológico y Seguimiento de Fauna Silvestre de Andalucía, Consejería de Medio Ambiente y Ordenación del Territorio of Junta de Andalucía, Spain. We thank M. Rendón for his help in the field and him, J. Aguilar Amat and G. Batanero for their useful comments. Part of this work was supported by data and infrastructure provided by INBO and VLIZ as part of the Flemish contribution to the LifeWatch observatory funded by FWO. The UvA-Bits tracking studies are facilitated by infrastructures for e-Science, developed with support of the NLeSC (http://www.esciencecenter.com/) and LifeWatch, carried out on the Dutch national e-infrastructure with support from the SURF Foundation. The data are held jointly by the BTO, University of Amsterdam, NIOZ, INBO and the funders of the project, and can be made available through their agreement. This work complied with Dutch law regarding ethical matters (#DEC-KNAW CL07.03). For birds in the U.K., tagging was undertaken under licence and approved by the independent Special Methods Technical Panel of the U.K. Ringing Scheme. This research was supported by Spanish National Plan project CGL2016-76067-P (AEI/FEDER, EU).Peer reviewe

Spatial patterns of weed dispersal by wintering gulls within and beyond an agricultural landscape

Non-frugivorous waterbirds disperse a wide variety of plants by endozoochory, providing longer-dispersal distances than other mechanisms. Many waterbirds visit both agricultural and natural landscapes during their daily movements, but potential bird-mediated dispersal of weed plants within and from agricultural landscapes to other habitats is commonly overlooked. Gulls (Laridae) are expanding in numbers and increasingly exploiting anthropogenic habitats worldwide, with possible growing implications for the spread of weeds. Yet, to date, there are no studies on the spatial distribution of weed dispersal by waterbirds. We developed a plant dispersal model based on movements of 19 Larus fuscus using ricefields, via GPS telemetry. We combined daily movements with two curves estimating the retention times of plant seeds in their guts: (a) an experimental curve based on retention time in captivity for four weeds with dry fruits known to be dispersed by gulls: Juncus bufonius, Cyperus difformis, Polypogon monspeliensis and the alien Amaranthus retroflexus; (b) a theoretical curve based on the interspecific scaling relationship between body mass and mean retention time. Median dispersal distances of weed plant seeds by gulls ranged between 690 and 940 m, but maximum distances exceeded 150 km. The theoretical retention time model showed higher median dispersal distances than the experimental retention time model. Spatial patterns of weed deposition were very similar between retention time methods, and most strongly depended on gull movements. Variation between individual gulls had little influence on seed shadows. About 92% of all seeds (>10,000 intact seeds per day) were dispersed within the ricefield area of 370 km2. The remaining 8% of seeds were deposited beyond ricefields into other habitats, 42% of which reached moist environments (other irrigated agriculture, rivers and natural wetlands) presumably suitable for weed establishment. Synthesis. Gulls can disperse weed plants over long distances across a mosaic of habitats. This implies exchange of weed plant species between human-dominated and natural areas by waterbirds as dispersal vectors. This spatial study highlights the importance of non-frugivorous birds for long-distance plant dispersal, which is generally an overlooked mechanism in studies aiming to predict and manage expansion of weed plants.Peer reviewe