Avian “Staycations” – The Phenomenon of Intratropical Migration

Juicy caterpillars, beachfront real estate, a mild, coastal climate and an accompanying band of paparazzi – all the ingredients of a perfect summer vacation! As birders and photographers rushed to document the largest known non-breeding concentration of Horsfield’s Bronze Cuckoos on vacation in Singapore, questions began to arise – Why are they here? Why would Australian birds, which enjoy comparatively mild winters, even need to migrate thousands of kilometres to spend the austral winter? In this article, we summarise available knowledge on the phenomenon of intratropical migration with reference to Australasian birds and shed some light on this poorly known aspect of avian migration.

An adult male Horsfield's Bronze Cuckoo at Punggol Barat, having a juicy caterpillar

An adult male Horsfield’s Bronze Cuckoo at Punggol Barat, having a juicy caterpillar

Australasia, a region comprising Australia, New Zealand, New Guinea and surrounding islands like New Caledonia, is generally regarded as a self-contained system with regard to avian migration. A study of bird migration in this region noted that only 30 shorebird and 10 landbird species which breed in the Northern Hemisphere regularly winter in the region (Dingle, 2004). However, there is significant avian movement within the region, involving species which birders might be familiar with.

Figure 1: Map showing the movements of Australasian migrants during the southern winter.

Figure 1: Map showing the possible movements of Australasian migrants during the southern winter.

In the south, globally threatened parrot species such as Swift and Orange-bellied Parrots migrate hundreds of kilometres from their breeding grounds in Tasmania to winter along southeast Australia. Further north, forest jewels such as the Buff-breasted Paradise Kingfisher, Noisy and Red-bellied Pittas and Rufous Fantail migrate from Queensland to spend the austral or southern winter (March – October) on the island of New Guinea (Pratt and Beehler, 2014). Similarly, large numbers of waterbirds make the journey north as well, wintering as far west as the Indonesian islands of Timor and Flores. It is believed that the number of migrating birds and distance they travel is related to the onset of winter temperatures in Australia as well as rainfall patterns during this period.

Buff-breasted Paradise Kingfisher from Cairns.  This stunning kingfisher breeds in northern Queensland during the southern summer but spends the winter on the island of New Guinea. Photo by Wang Bin.

Buff-breasted Paradise Kingfisher from Cairns. This stunning kingfisher breeds in northern Queensland during the southern summer but spends the winter on the island of New Guinea. Photo by Wang Bin.

Until recently, it was thought that no Australasian breeding birds enter Asia beyond Wallace’s Line, a boundary separating the faunal regions of Asia and Australia (Dingle, 2009). However, with an increase in observer coverage, we now know that a small number of Australasian birds regularly visit Asia during the austral winter. In recent years, Sacred Kingfisher has been recorded from Borneo with some regularity, while further west Horsfield’s Bronze Cuckoo has now been recorded annually in Singapore, with small numbers reaching as far north as Penang Island in the current irruption.

Horsfield's Bronze-Cuckoo from Penang, Malaysia. Photo courtesy of Choy Wai Mun.

Horsfield’s Bronze-Cuckoo from Penang, Malaysia. Photo courtesy of Choy Wai Mun.

The lengthy migrations undertaken by these two species are particularly surprising given that both are habitat generalists, able to survive in a wide variety of environments ranging from coastal scrub to urban gardens. As such, one would expect there to be sufficient areas of suitable habitat within Australasia for them to spend the winter, so why the Malay Peninsula?

One possibility is the cold snap that was experienced throughout most of eastern Australia in the first week of June. Many areas experienced subzero overnight temperatures and it is possible that the sudden onset of cold weather might have triggered eastern populations of the Horsfield’s Bronze Cuckoo to migrate further north than they usually do. In view of the territoriality demonstrated by birds on wintering grounds, it is plausible that given the potentially large number of birds involved, immatures and older adults might have been forced to winter at the limits of their wintering range along the Malay Peninsula, with suitable areas closer to Australia occupied by territorial adults in their prime.

Interestingly, these cuckoos do not stay for more than a week or two from the time of their first sighting in Singapore. It is recommended that birders continuing to document the cuckoos at Punggol Barat make notes of the dates on which they observed the birds as well as the number observed. On a regional scale, with the advent of geolocator technology (a kind of miniature tag to monitor the movement of animals), long distance austral migrants like the Horsfield’s Bronze Cuckoo could serve as an excellent study species for mapping the migratory routes of Australasian birds during the austral winter, thereby unravelling the mysteries of this poorly understood aspect of avian migration.

Literature Cited
Dingle, H. (2004). The Australo-Papuan bird migration system: another consequence of Wallace’s Line. Emu, 104(2), 95-108.

Dingle, H. (2009). ROWLEY REVIEW. Bird migration in the southern hemisphere: a review comparing continents. Emu, 108(4), 341-359.

Pratt, T. K., & Beehler, B. M. (2014). Birds of New Guinea. Princeton University Press.

Photo Gallery

Author: Albert Low

Advertisements

3 thoughts on “Avian “Staycations” – The Phenomenon of Intratropical Migration

  1. Pingback: Big Year 2015: May-June summary | Dig deep

  2. Neoh Hor Kee

    Great article. Don’t forget the seabirds that nest in Australia that make epic journeys up north starting from the onset of the Austral winter in April. Up here in the waters off Kedah, we have been recording small numbers of Short-Tailed Shearwaters that typically appear between late April to early June. These birds nest off Tasmania and South Australia and make the second-longest journeys of any bird after the Arctic Tern – they go right up to the Bering Sea, down the west coast of North America and then fly diagonally across the pacific Ocean back to Australia by October.

    Like

    Reply
    1. Alan OwYong Post author

      Hor Kee, many thanks for the reminder. Our last pelagic is usually in May to see what seabirds are using the straits at this time of the year. We accepted our first record of the Short-tailed Shearwater based on a photo of one taken during a Pelagic survey on Jan 2013. We had a previous off shore record on June 1998 but confusion with other similar species could not be discounted. Great to exchange info on the movement of these seabirds. Best Alan.

      Like

      Reply

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s