Seabird breeding timing at high latitudes

Seabird breeding timing at high latitudes

Top image: Black-legged kittiwakes and Brünnich’s guillemots with chicks on Spitsbergen. Guillemots lay their eggs on bare rock. All the nest material seen here comes from the kittiwake nests. Photo: Øystein Varpe/UNIS

Imagine an Arctic bird cliff in summer, teeming with fledging chicks and predators waiting below. Now fast-forward to a short time later and picture a quiet breeding cliff dusted in snow. What evolutionary adaptations and constraints shape when birds breed in seasonal environments? And when conditions change, will birds breed at the “right” time?

23 June 2016
Text: Zofia Burr and Øystein Varpe, UNIS

Animals living at high latitudes must adapt to environments where the physical and biological conditions go through extreme changes throughout the year. Phenology, the study of recurring biological phenomena, is one piece of the puzzle needed to understand how animals have evolved strategies to deal with strong seasonality. Seabirds, in addition to being charismatic, are great study subjects because it is far easier to study individual birds than individual fish or plankton, and understanding their breeding timing strategies helps shed light on ecological interactions.

For many species, the timing of when parents re-produce has consequences on the survival of their young. In 1914, Norway’s Johan Hjort put forth the idea that fish larvae must have the appropriate prey at the time they hatch in order to survive. This concept has inspired much work on timing across trophic levels. Of course food is an essential part of successful reproduction for birds as well, but factors such as predators, competition with other birds, and the need to finish breeding before summer ends and harsh physical conditions kick in at high latitudes, might also influence when a mother lays her eggs.

At first glance, different seabird species may seem similar to one another, yet they each have specific ood sources and behaviours. This leads us to wonder – how do species differ in the strategies they use to time breeding?

We have joined forces with a network of biologists whose work within the SEAPOP programme includes monitoring seabird breeding perfomance at “key sites” along a wide latitudinal gradient in Norway and Svalbard. With support from Fram Centre incentive funding, 12 people representing 7 institutions are working together to understand large-scale variability in seabird breeding timing.

Observer monitors nesting black-legged kittiwakes on Spitsbergen. Photo: Øystein Varpe/UNIS

Observer monitors nesting black-legged kittiwakes on Spitsbergen. Photo: Øystein Varpe/UNIS

We quantified breeding timing at ten colonies along the Norwegian coast to Spitsbergen (65–79 °N) for four seabird species (Atlantic puffin, black-legged kittiwake, and common and Brünnich’s guillemots) and asked how timing varied between species and over a large spatial scale.

Because spring comes later to higher latitudes, we expected to see later breeding at higher latitudes, and that is what we found. However, different species had different patterns of breeding synchronicity, or how closely in time the individuals at each colony were breeding. For the kittiwake, breeding synchronicity increased with increasing latitude. This suggests that as the summers get shorter, the birds breed within a narrower window of time. Tycho Anker-Nilssen, who leads monitoring efforts at Røst in Lofoten, one of the more southern latitudes represented in the study, shared his first-hand accounts: “In terms of weather, the window for nice breeding conditions is of course larger than further north, yet my feeling is that it also has very much to do with food availability. On top of this, it seems that extensive egg predation (especially by ravens) in parts of the colony acts to reduce clutch size and delay hatching for many pairs.” So in low latitudes we see a wide range of hatching dates, and sometimes summers are also long enough for a new clutch to be laid if the first is lost. However, this may not be the case at the highest latitudes, such as on Spitsbergen.

In contrast to kittiwakes, two species of guillemots (Brünnich’s and common) were breeding synchronously at all colonies in our study, not just at the highest latitudes. Sébastien Descamps, a biologist working at colonies in Isfjorden, comments on why we think we see this pattern. “On Spitsbergen, we see the guillemot chicks fledging quite synchronously, within a few days, which is likely advantageous from their perspective since predators such as foxes and glaucous gulls often go after the chicks for prey. Jumping all together decreases the probability of getting caught by a predator!” This strategy, known as “predator swamping”, could explain why the guillemots schedule breeding synchronously at all study colonies, unlike the kittiwakes.

Puffin breeding times show a less distinct pattern than those of the other species. Unlike kittiwakes, puffins showed no significant change in synchronicity with increasing latitude, nor was breeding as consistently synchronous as it was for guillemots.

Our results tell us two main things: species differ in their timing strategies, and various components of timing (for example, breeding synchronicity vs average timing) are shaped by different processes. Given that species have different strategies to time their breeding, they will likely face different challenges when it comes to successfully raising their chicks. Perhaps under changing environmental conditions, some species will have difficulties adjusting to new conditions and end up breeding at sub-optimal times, thereby risking reduced reproductive success.

Figure showing hatching time distributions of some seabirds in Svalbard and Northern Norway. Author: Zofia Burr

Figure: Zofia Burr

Further reading:
Later at higher latitudes: large-scale variability in seabird breeding timing and synchronicity – Article in Ecosphere

Researchers from many institutes and disciplines joined forces for this project. Several of the collaborators are responsible for key sites in the SEAPOP programme, which has been producing important results on seabird population dynamics for more than a decade.

Zofia M. Burr, UNIS and the University of Bergen
Øystein Varpe, UNIS and Akvaplan-niva
Tycho Anker-Nilssen, NINA
Kjell Einar Erikstad, NINA and NTNU
Sébastien Descamps, NPI
Robert T. Barrett, UiT The Arctic University of Norway
Claus Bech, NTNU
Signe Christensen-Dalsgaard, NINA and NTNU
Svein-Håkon Lorentsen, NINA
Børge Moe, NINA
Tone Kristin Reiertsen, NINA
Hallvard Strøm, NPI

UNIS – University Centre in Svalbard
NTNU – Norwegian University of Science and Technology
NINA – Norwegian Institute for Nature Research
NPI – Norwegian Polar Institute

Article originally published in Fram Forum 2016

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