To be Jealous of a Goose: The Marvels of Migration

Figure 1: Brent Goose at Bull Island by Angelo Failla
Figure 1: Brent Geese at Bull Island by Angelo Failla

It’s a Strange Thing Being Jealous of a Goose

It’s not a feeling I expected to have at this stage in my life, or at any stage in my life come to think of it. It’s irrational jealousy too. A goose on paper hasn’t the most appealing life. If I donned my Zoological glasses I would even say it’s quite a difficult existence the Irish wintering Brent geese have forged for themselves. They arrive around October after their long journey from the East Canadian tundra. They must feast almost continuously on eelgrass (Zostera species) to even have a chance of making it back to their breeding grounds. In the later months of their winter stay, this is supplemented by terrestrial grasses from the local parks and rugby pitches. This diet is certainly not the source of my envy. Vegetarianism aside, that’s too much green for me. 

Arguably the more difficult feat, the migration itself, is the aspect of their life histories that sparks my flicker of jealousy. Make no mistake, this is a difficult journey, a long flight to escape the certain death an arctic winter brings. They break only briefly in western Iceland before touching down in Strangford Lough, County Down where refuelling on Zostera soon commences. Convinced yet on the perks of being a Goose? I did say there may be a touch of irrationality to this but do hear me out. The current pandemic has certainly clipped our wings when it comes to travelling and in my idle time, the Brent geese stand as a reminder of an out of grasp wider world. I have always found migrations of entire populations of animals across the world to be a fascinating aspect of nature. I must admit whenever I thought of migrations up until recently, the Wildebeest on the great plains of Africa or the Grey Whales of the Pacific sprung to mind. This winter though with travel out of the question, my usual joy of seeing the Brent geese has come with a touch of poignancy. When will we be able to move again?

Figure 2: Brent Goose in Tralee Bay by Moss Carey
Figure 2: Brent Geese in Tralee Bay by Moss Carey Photo courtesy of the author

It is a Fascinating Phenomenon Though, this Business of Migration

It’s a lifestyle that crops up all over the animal kingdom. I have a particular fondness for birds (a natural progression from a childhood obsession with dinosaurs). I read a captivating book on the infamous Cuckoo by the celebrated behavioural ecologist Nick Davies, which along with many other things described the momentous migrations of these birds from fens in England to the jungles of the Democratic Republic of Congo. Arctic Terns have been recorded travelling over 80,000km in a single year going as far as Antarctica for the Southern Hemisphere summer and as their name suggests up towards the Arctic for the summer in the North. A truly phenomenal journey. Many breed along the coast of Ireland, with Kerry, Mayo, Donegal, and Wexford having large populations. 

However, migration is not confined to birds. Gray whales migrate up to 12,000km from their breeding grounds in the central Pacific down near the west coast of Mexico to their feeding grounds in the Arctic. Salmon migrate back from the ocean into the freshwater streams of their birth using gradients in salinity to guide them back to their originating rivers. Even some species of insect migrate; the Monarch butterflies being some of the most widely known examples. Monarchs move down through North America to winter in California and Mexico. Theirs is a strange migration involving one generational journey down South followed by a successive multi-generational travel back North. It is still somewhat of a mystery how successive generations navigate their way back to the same overwintering habitat that generations previously left. 

Why migrate though? Why take on these momentous journeys at all? I’m sure we can all think of plenty of reasons why we’d like to travel at the moment, but what’s the evolutionary advantage for animals? To take the case of the light bellied Brent goose (this is the subspecies that relocates to Ireland for the winter), and for a lot of other migrants it boils down to seasonality. By summering in the arctic tundra, the geese take advantage of the short but very productive growing season. The conditions and forage quality of the arctic summer are more favourable for the geese than those during the Irish summer and they take this opportunity to breed and raise their young. While the summers in the Arctic are advantageous for the geese, wintering in the tundra is not an option, with average winter temperatures coming in at -34 degrees Celsius. The much milder conditions in Ireland. as well as the beds of Zostera around estuaries, mean that from an evolutionary perspective the benefits of migration vastly outweigh the costs. So, from about October to March up to 30,000 geese land on our shores.

For my part of the country, I can expect about 7,000 light bellied Brent geese to take up residence in Dublin Bay. The majority will flock around Bull Island, but a few will venture towards Booterstown Marsh, setting up camp often near a newly forming sand spit just past the DART line. Numbers do vary from year to year and the availability of Zostera can have a big impact. A large decline in the eelgrass back in the 1930s was cataclysmic for the Irish wintering population numbers. Harsher conditions at their breeding site as well as artic fox density can significantly impact survival rates.

Unfortunately, There May be a New Threat on the Horizon…

and it could be impactful on migrations across many species. Climate Change rears its head in the environmental dynamics associated with migration. Phenological studies involve the investigation into how seasonality influences the onset of biological events such as migration. There have been growing worries in the scientific community that climate change will lead to a mismatch in the timing of usually co-occurring aspects of life histories. One of these worries relates to migrators. The effects of Global Warming are felt most dramatically at the Poles and an earlier onset of spring there may not be mirrored by increasing temperatures at lower latitudes.

Returning to the Brent geese but taking a step back from the Irish population, a team of researchers in Denmark have been looking into how this mismatch may affect the small population of light bellied Brent geese that winter in Denmark and breed on Svalbard, an Arctic archipelago. The temperatures at their overwintering grounds at the start of spring have not increased significantly. However, at Svalbard, the time at which the growing season starts is happening earlier and earlier. The Brent geese, therefore, have not been altering the time at which they leave Denmark and have been arriving later and later into the season at Svalbard, missing out on that initial growth. The Denmark team have suggested that the late arrival of the Brent’s at Svalbard could be a contributing factor to the declining population numbers. 

It is worrying to realise that there is a fragile element to migrations in the face of climate change. Even though I remain envious of their long travels, it is a real privilege to have long-distance migrators land on our shores. While at this moment we are limited in our movements, the great migrations remind me of the awe-inspiring scale of the natural world and that one day soon the exploration of it will be once again limitless. I hope that the moments of magic that nature has provided us with over these lockdowns will inspire us towards a more caring, considerate, and responsible attitude for the natural world and its many wonders. 

Have a Gander at our other articles relating to the Brent Goose, Climate Change and Migration:

A “Tern” up for the books – Conservation success for Roseate Terns on Rockabill Island

Swanning Around: True Love and Rude Boats


Managing river connectivity and fish migration in a water stressed country: considerations from South Africa

Overheating Earth: What YOU Can Do to Counter Climate Change



  1. “Light-bellied Brent Goose” by pallotron is licensed under CC BY-NC-SA 2.0
  2. Cleasby, I.R., Bodey, T.W., Vigfusdottir, F., McDonald, J.L., McElwaine, G., Mackie, K., Colhoun, K. and Bearhop, S., 2017. Climatic conditions produce contrasting influences on demographic traits in a long?distance Arctic migrant. Journal of Animal Ecology86(2), pp.285-295.
  3. Tinkler, E., Montgomery, W.I. and Elwood, R.W., 2009. Foraging ecology, fluctuating food availability and energetics of wintering Brent geese. Journal of Zoology278(4), pp.313-323.
  4. “Tralee. Light bellied Brent Geese” by Myrtle26 is licensed under CC BY-SA 2.0
  5. 2021. Gray Whale Breaks Mammal Migration Record. [online] Available at: <> [Accessed 29 March 2021].
  6. BirdWatch Ireland. 2017. Species Focus Brent Goose. [ONLINE] Available at: [Accessed 29 March 2021].
  7. Reppert, S.M. and de Roode, J.C., 2018. Demystifying monarch butterfly migration. Current Biology28(17), pp.R1009-R1022.
  8. Clausen, K.K. and Clausen, P., 2013. Earlier Arctic springs cause phenological mismatch in long-distance migrants. Oecologia173(3), pp.1101-1112.
About Daniel Dunleavy 1 Article
Daniel Dunleavy is a zoology graduate from Trinity College with an aim to further study sociality and foraging behaviour. He has a wide interest in animal behaviour and evolution spanning from kin selection to migration. In college, he was chair of the Zoological Society and really enjoyed communicating about various aspects of zoology to wider audiences. He has been a keen birdwatcher since a young age and loves highlighting the aspects of local wildlife that inspired him to pursue zoology.

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