Temporal non-independence of foraging dive and surface duration sequences in the European shag Gulosus aristotelis

Studies of foraging behaviour and respiratory physiology in breath-holding divers often assume that each dive cycle (dive plus surface duration) is physiologically and ecologically independent within a series (or “bout”) of sequential dives. We tested this assumption using time depth recorders and GPS data for more than 42,000 dives in 1289 bouts by 39 pairs of male and female European shags (Gulosus aristotelis) provisioning nestlings. We found distinct patterns of temporal autocorrelation over several dives within bouts, but this was driven mainly by consecutive dives of the same type, that is, runs of V-shaped (presumably prey searching) versus U-shaped (presumably active hunting) dives. We found no evidence of cumulative physiological effects (i.e. fatigue and/or lowered body temperature) across dives within a bout. However, within-individual variation in dive behaviour revealed complex interactions. Longer bouts were associated with more V-shaped dives, including more and longer runs of V-shaped dives. Meanwhile, more U-shaped dives and longer runs of U-shaped dives acted as limiting factors to bout lengths, with longer bouts being associated with more U-shaped dives only later in the bout. Interactions between bout length and body mass, and between dive order within the bout and body mass, also suggested various size-specific patterns in the temporal distribution of U-shaped dives. Long bouts and bouts ending in longer runs of V-shaped dives were more likely to indicate the termination of foraging activity. However, neither dive type nor bout length predicted whether individuals subsequently (i) stayed to forage in the same location or (ii) moved to a new location to continue foraging within the same trip from the nest. European shags therefore showed temporal non-independence across successive dive cycles and successive bouts of dives, likely as a result of temporal and spatial variation in prey availabilities rather than cumulative physiological effects that might contravene the assumptions in models of optimal dive behaviour. dive behaviour, dive cycles, foraging behaviour, marginal value theorem, physiological constraints, TDR, telemetry, temporal autocorrelationpublishedVersio

Fish consumption by great cormorants in Norwegian coastal waters—a human-wildlife conflict for wrasses, but not gadids

Piscivorous wildlife is often perceived as competitors by humans. Great cormorants of the continental subspecies (Phalacrocorax carbo sinensis) in the Baltic and North Sea increase, while local cod (Gadus morhua) stocks decline. In contrast, numbers of the Atlantic subspecies (Phalacrocorax carbo carbo), breeding along the Norwegian and Barents Seas, have been relatively stable. We investigated the diet of both great cormorant subspecies in breeding colonies along the Norwegian Coast from Lofoten to the Skagerrak and estimated the biomass of fish consumed annually by great cormorants in Norwegian waters. The birds’ consumption was compared with estimated fish stock sizes and fishery catches. Cod and saithe (Pollachius virens) dominated the diet in the Norwegian Sea and wrasses in the North Sea and Skagerrak. Estimated total fish consumption of cod and saithe by great cormorants was <1.7% of estimated fish stocks and <9% of that of human catches and therefore considered minor. Cormorant consumption of wrasses amounted to 110% of human catches. The practice of using wrasses as cleaner fish in the salmon farming industry leads to a conflict with cormorants, and we urge for a better understanding and management of wrasse populations, taking ecosystem functioning and natural predation into account. diet analysis, fish stock size, Gadus morhua, Labridae, metabolic rate, North Atlantic, NorwaypublishedVersio

Foraging behaviour of black guillemots at three Norwegian sites during the breeding season

The intensifcation of coastal development poses potential threats for coastal seabirds, and understanding their habitat use is a key factor to guide conservation and management. In sub-arctic areas, black guillemots (Cepphus grylle) use coastal habitats year-round, which makes them vulnerable to the increasing human activities in these areas. In mainland Norway, one of the species’ strongholds, black guillemots are red-listed after substantial population declines. However, their fnescale foraging behaviour has received little attention to date. We collected and analysed GPS tracking data from adult black guillemots at three sites located over a latitudinal gradient of 250 km in central/northern Norway. Maximum foraging ranges of 33 km at Sklinna (65°12′N) for incubating birds, and 18 km at both Vega (65°34′N) and Sklinna for chick-rearing birds, are among the longest reported for this species. At all three sites, foraging probability was highest in shallow waters (<50 m depth) close to the colony and declined with increasing water depth and distance from colony. However, birds from Vega also foraged over deeper waters. Kelp presence was of high importance at Sklinna, but apparently less important at Røst (67°26’N) and Vega. We also found distinct diferences in foraging activity across the day and with tidal height among the sites. Inter-site diferences in habitat use and foraging activity may be explained by diferences in the availability of habitats and suitable prey. Our study highlights the importance of shallow marine areas for black guillemots and shows that habitat use can vary substantially between sites. Cepphus grylle · Marine spatial planning · Habitat use · Species distribution model · Kelp forestpublishedVersio

Kystvann (bunn og pelagisk)

Norge har en kystlinje på ca. 2500 km målt langs den såkalte grunnlinjen fra svenskegrensen til Grense Jakobselv. Grunnlinjen trekkes mellom ytterpunktene på landformasjoner som stikker opp over vannflaten. Målt langs land inkludert øyer, fjorder og bukter er kystlinjen mer enn 80 000 km, som tilsvarer to ganger jordens omkrets ved ekvator. Som kystvann regnes i denne forbindelse alle indre farvann og sjøområdene innenfor en nautisk mil (1852 m) utenfor grunnlinjen. Denne avgrensningen er en praktisk grense som er definert i forbindelse med EUs vanndirektiv og som derfor vil bli benyttet i framtidig miljøovervåking av norsk kystvann. Kystvannet omfatter et spekter av naturtyper fra fjæresonen til store dyp (1301 m dyp i Sogne fjorden). Vannmassene utgjøres i hovedsak av den norske kyststrømmen som strømmer nordover langs hele kysten, og Atlanterhavsvann utenfor og under denne (Brattegard & Holthe 1995; Rinde et al. 1998). Vannet i kyststrømmen oppblandes med tilført elvevann og har lavere saltinnhold enn Atlanterhavs vannet. Inne i fjordene kan vannmassene være markert sjiktet med et ferskvannspreget overflatelag som kan bli betydelig oppvarmet om sommeren, og et betydelig saltere dypvann som holder lav temperatur året rundt. Organismesamfunnene i de frie vannmassene er preget av forholdsvis korte næringskjeder fra planteplankton og dyreplankton til fisk, sjøfugl og sjøpattedyr. Produksjonen i vannmassene står i nær forbindelse med havområdene omkring, men er generelt høyere i kystvannet på grunn av tilførsler av næringsemner fra land. Bunnsystemene i kystvannet kan grovt inn deles i hardbunn (fjell og stein) og bløtbunn (leire, mudder, sand, grus). Utformingen bestemmes av lokale strømforhold og bølgepåvirkning. I tillegg til bunnforholdene er faktorer som lys, oksygentilgang, saltholdighet og temperatur avgjørende for hvilke organismer som forekommer. I norske farvann er det tilstrekkelig lys for plantevekst ned til 30-40 meter dyp. Hardbunn på grunt vann domineres av tang, tare og andre fastsittende alger, mens bløtbunn kan ha tett vegetasjon av sjøgress. Bunnområder med velutviklet vegetasjon av tare eller sjøgress har stor biologisk produksjon og er ofte svært artsrike. I fjorder og indre kystområder hvor det tilføres ferskvann er saltholdigheten ofte nedsatt i de øverste vannlagene. Disse systemene kan ha helt spesielle organismesamfunn. I brakkvann med permanent nedsatt saltholdighet kan få arter klare seg, men disse er gjerne spesialiserte og finnes ikke andre steder. Det foreligger ikke sikre tall for antall arter i kystvannet, men overslag antyder opp mot 10 000 arter. Disse inkluderer mer enn 1000 encellede alger, hvorav drøyt 700 lever fritt i vannmassene, og 1000-2000 encellede dyr, omkring 500 fastsittende flercellede alger og opp mot 5000 flercellede virvelløse dyr (Brattegard & Holthe 2001; Bakken et al. 2005). Av fisk forekommer omkring 150 arter i kystvannet, hvorav riktignok en god del er tilfeldige gjester fra mer sydlige farvann. Av fugl er det omkring 60 arter som i større eller mindre grad er knyttet til kysten, mens det for pattedyr kan regnes et titall arter av sel, hval og landpattedyr (oter, mink). Kystsonen har stor betydning for produksjon av marint materiale, for rekreasjon og opplevelse og for produksjon av oppdrettsorganismer. Samtidig er kystsonen utsatt for en rekke påvirkninger fra menneskelig virksomhet. De viktigste påvirkningene utgjøres av forurensninger, overgjødsling av nærings salter (eutrofi), ødeleggelse av arters leveområder og overbeskatning av bestander. I senere år er man blitt klar over at ødeleggelse av leveområder er viktigere enn tidligere antatt og rammer både arter i spesielle miljøer og vanlig forekommende arter som i deler av sin livssyklus er knyttet til visse naturtyper. I tillegg er kyst vannet i endring som følge av stigende temperatur og mulig framtidig forsuring. Nye trusler kommer også fra fremmede arter som i økende grad finner innpass i kystsonen. Kystsonen er utsatt både for langtransporterte påvirkninger som forurensning og næringssalter som tilføres med havstrømmer og fra lokale kilder ved utslipp til sjø

Diverging phenological responses of Arctic seabirds to an earlier spring

The timing of annual events such as reproduction is a critical component of how free‐living organisms respond to ongoing climate change. This may be especially true in the Arctic, which is disproportionally impacted by climate warming. Here, we show that Arctic seabirds responded to climate change by moving the start of their reproduction earlier, coincident with an advancing onset of spring and that their response is phylogenetically and spatially structured. The phylogenetic signal is likely driven by seabird foraging behavior. Surface‐feeding species advanced their reproduction in the last 35 years while diving species showed remarkably stable breeding timing. The earlier reproduction for Arctic surface‐feeding birds was significant in the Pacific only, where spring advancement was most pronounced. In both the Atlantic and Pacific, seabirds with a long breeding season showed a greater response to the advancement of spring than seabirds with a short breeding season. Our results emphasize that spatial variation, phylogeny, and life history are important considerations in seabird phenological response to climate change and highlight the key role played by the species' foraging behavior

Earlier colony arrival but no trend in hatching timing in two congeneric seabirds (Uria spp.) across the North Atlantic

A global analysis recently showed that seabird breeding phenology (as the timing of egg-laying and hatching) does not, on average, respond to temperature changes or advance with time (Keogan et al. 2018 Nat. Clim. Change8, 313–318). This group, the most threatened of all birds, is therefore prone to spatio-temporal mismatches with their food resources. Yet, other aspects of the breeding phenology may also have a marked influence on breeding success, such as the arrival date of adults at the breeding site following winter migration. Here, we used a large tracking dataset of two congeneric seabirds breeding in 14 colonies across 18° latitudes, to show that arrival date at the colony was highly variable between colonies and species (ranging 80 days) and advanced 1.4 days/year while timing of egg-laying remained unchanged, resulting in an increasing pre-laying duration between 2009 and 2018. Thus, we demonstrate that potentially not all components of seabird breeding phenology are insensitive to changing environmental conditions

Twilight foraging enables European shags to survive the winter across their latitudinal range

Species breeding at high latitudes face a significant challenge of surviving the winter. Such conditions are particularly severe for diurnal marine endotherms such as seabirds. A critical question is therefore what behavioural strategies such species adopt to maximise survival probability. We tested 3 hypotheses: (1) they migrate to lower latitudes to exploit longer day length (‘sun-chasing’), (2) they forage at night (‘night-feeding’), or (3) they target high-quality food patches to minimise foraging time (‘feasting’). We studied the winter migration and foraging strategies of European shags Phalacrocorax aristotelis from 6 colonies across a latitudinal gradient from temperate regions to north of the Arctic Circle using geolocators deployed over 11 winters. We found evidence for ‘sun-chasing’, whereby average southerly movements were greatest from colonies at higher latitudes. However, a proportion of individuals from higher latitudes remained resident in winter and, in the absence of daylight, they foraged during twilight and only very occasionally during the night. At lower latitudes, there was little evidence that individuals migrated south, nocturnal feeding was absent, and twilight feeding was infrequent, suggesting that there was sufficient daylight in winter. There was no evidence that winter foraging time was lowest at higher latitudes, as predicted by the ‘feasting’ hypothesis. Our results suggest that shags adopt different behavioural strategies to survive the winter across their latitudinal range, dictated by the differing light constraints. Our study highlights the value of multi-colony studies in testing key hypotheses to explain population persistence in seabird species that occur over large latitudinal ranges

Six pelagic seabird species of the North Atlantic engage in a fly-and-forage strategy during their migratory movements

Bird migration is commonly defined as a seasonal movement between breeding and non-breeding grounds. It generally involves relatively straight and directed large-scale movements, with a latitudinal change, and specific daily activity patterns comprising less or no foraging and more traveling time. Our main objective was to describe how this general definition applies to seabirds. We investigated migration characteristics of 6 pelagic seabird species (little auk Alle alle, Atlantic puffin Fratercula arctica, common guillemot Uria aalge, Brünnich’s guillemot U. lomvia, black-legged kittiwake Rissa tridactyla and northern fulmars Fulmarus glacialis). We analysed an extensive geolocator positional and saltwater immersion dataset from 29 colonies in the North-East Atlantic and across several years (2008-2019). We used a novel method to identify active migration periods based on segmentation of time series of track characteristics (latitude, longitude, net-squared displacement). Additionally, we used the saltwater immersion data of geolocators to infer bird activity. We found that the 6 species had, on average, 3 to 4 migration periods and 2 to 3 distinct stationary areas during the non-breeding season. On average, seabirds spent the winter at lower latitudes than their breeding colonies and followed specific migration routes rather than non-directionally dispersing from their colonies. Differences in daily activity patterns were small between migratory and stationary periods, suggesting that all species continued to forage and rest while migrating, engaging in a ‘fly-and-forage’ migratory strategy. We thereby demonstrate the importance of habitats visited during seabird migrations as those that are not just flown over, but which may be important for re-fuelling.publishedVersio