Death from Above
Posted on: June 18, 2014
Author: Ian Davies
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In the fifth and final year of work at the Canning River for the Arctic Shorebird Demographics Network (ASDN) , one would expect to have a good idea of what the birds will be doing in any given year.
So far the first two weeks of this season have been full of surprising and unusual trends, both with the numbers of certain species nesting and the behavior of those species. The changes we are seeing now in the early part of the season show how important it is to collect long-term data in vital locations like the Arctic. Even in a short few years we are gaining new insights into the lives and ecology of these species that would be impossible to ascertain in a single field season.
There are five species that we call our ‘focal species’ and they are the birds we concentrate our efforts on. These birds are: Semipalmated Sandpiper, Pectoral Sandpiper, Dunlin, Red-necked Phalarope, and Red Phalarope. The number of nests that we find for each of these species varies from year to year, but we usually recover around 60-80 Semipalmated Sandpiper, 8-15 Dunlin, 30-60 Red-necked Phalarope, and 30-60 Red Phalarope nests.
The Pectoral Sandpiper, the one species not listed above, is the most unpredictable of them all. Pectorals show less site faithfulness compared to the other four focal species, so we haven’t seen the same birds returning year after year. Their wandering tendencies mean that some years we have recovered few and in other years we have recovered many.
Our lowest nest recovery in a season was less than 20 Pectoral Sandpipers nests, but the high record before this year was around 80 nests. As it stands on June 17, we have found 93 Pectoral nests, and we could easily exceed 130 nests this season for this one species alone.
Aside from our focal species, the other winged residents of the study area vary in abundance between years. This year we have noticed an unusually large number of aerial predators in the area. The most common predatory birds in Canning River are the three species of jaegers (Pomarine, Parasitic, and Long-tailed), Short-eared Owls, and Snowy Owls. There are also some Rough-legged Hawks, Northern Harriers, and Peregrine Falcons that travel 30+ miles from the mountains to hunt the coastal plain.
Normally we will see small numbers of Pomarine and Parasitic Jaegers daily, with Long-tailed Jaegers showing every couple days in singles or small flocks, and Short-eared and Snowy Owls every couple of days. This year we have seen all of these species almost every day, and we saw 60+ Pomarine Jaegers and seven Short-eared Owls in one day! We have also found single nests of Pomarine and Parasitic Jaegers and Snowy and Short-eared Owls already, and it is likely that there will be more on the way.
So what does the presence of all these predators mean for the shorebirds? The predators are mostly here to feed on lemmings, but they will take a bird every now and then if a chance presents itself. The most striking response to this new threat is that we have noticed the shorebirds completely changing their behavior around the nest. Compared to the behaviors we have observed over the past four years, it’s like we’re dealing with different species!
Semipalmated Sandpipers normally fly away when we are within 5-30 meters of the nest, which gives us a good distance to maximize nest-finding success. Pectoral Sandpipers are usually more sensitive to us than the Semipalmated Sandpipers are and often fly away when we are 30-80 meters away, which makes it much more difficult to locate the nests because the possible range is larger.
This year all of the species are sitting much longer on their nests. The Semipalmated Sandpipers are seeming to stay on their eggs until we are 1-8 meters away, and Pectorals are flying away when we are 15-30 meters away.
This means that we are finding many fewer Semipalmated Sandpiper nests than average (34 to date), and lots of Pectorals (up to 93 nests as stated above). Phalaropes nest later than the other species, so it is still early to know how their behavior will be affected, but the changes so far are nothing short of fascinating.
The interesting thing is that many of the birds that are showing different behavior this year are returning individuals from past years. This suggests that they are able to adapt their behavior on a local scale based on the predators that are present each year – pretty amazing! It sounds like a graduate research project just waiting to be done.
Many of the other species here are also susceptible to the presence of predators. The waterfowl that nest here are a prime example of this. The nesting Cackling Geese and Brant often fall victim to marauding Arctic Foxes as do the King Eider and Northern Pintail that make up most of our duck nests.
We also see Common Eider occasionally, and the rare Spectacled Eider has nested here once during the study. So far this year we have seen three pairs of Spectacled Eider, but no sign of nesting yet. Eider show some of the most stunning plumage that you could ever hope for in a duck, and their fluffy down is world famous.
As we start to discover more shorebird nests, we will see the effects of Arctic Foxes and avian predators on the remainder of the nesting period.
It is a tough life on the tundra, for any bird or organism. As I write this from the interior of our cook tent, the wind is howling around 30 mph outside, the temperature is in the mid 30′s, and the summer solstice is less than a week away. But I, like the birds, wouldn’t trade it for the world.