Sunday, 27 January 2013

Tawny Frogmouth Breeding Success

Former Grampian ringer Stuart Rae now lives in Canberra, Australia. Here he shares one of his studies on the local birdlife.

A brood of two Tawny Frogmouth chicks

I have been monitoring the breeding success of Tawny Frogmouths Podargus strigoides in Canberra, Australia, for several years and have found that the pattern is fairly constant. About half the breeding pairs rear two young to fledging; a few rear three in any year and about a quarter rear one chick. The proportion of pairs which fail to rear any chicks is about 24% on average over the years, ranging from 17 – 34% (Figure 1). I do not disturb the birds to record clutch size, but it is known to range from 1-3.

Figure 1: The number of young reared per breeding pair of Tawny Frogmouths in 2006- 2012, Canberra, Australia.

In recent years I had thought that more birds were failing to rear young, but this is just the impression gained as I have added more pairs to the study in the past few years. Although I have been recording more failures, this has been in proportion with larger sample sizes, there is no statistical difference (χ2 = 3.8, df = 6, P = 0.43). The main causes of failure, which is usually of whole clutches or broods, are predation by unknown species, but likely Brush-tailed Possum or Brown Goshawk. One male was taken off the nest by a feral cat. A few nests have been blown out of their trees by strong winds.

Figure 2: the number of Tawny Frogmouth pairs which fail to rear any young in any year is proportional (c 24%) to the number of pairs studied (r = 0.899, P = 0.003).

Further study will aim to determine whether there are any differences between the breeding success of frogmouths in grassy woodland, dry sclerophyll forest or suburban remnant woodland; or if there is any difference between years of drought and high rainfall. Fortunately the study has already covered these criteria.

Stuart Rae

A male Tawny Frogmouth protects his chick

Thursday, 17 January 2013

A Great Great Black-Backed Gull

The last post about colour ringed gulls on this blog was about a rare movement, a Common Gull chick seen in North West Spain. We have now had another unusual movement to Spain from one of our gull chicks. Not only was it ringed on the same day, but it has been sighted only 7 miles away from our Common Gull! This time however it is a Great Black-backed Gull.

On the 30th June 2012, after a morning’s ringing of 180 Common Gull chicks at Tillypronie, we headed to the coast, to Whinnyfold seabird colony. There we ringed 90 gull chicks on a tidal stack (above). Most of the chicks were Herring Gulls, but we also colour ringed 3 Great Black-backed Gulls (below), the first and only chicks of this species to be ringed in our project.

We heard no reports from these birds until 13th January 2013, when T:013 was sighted at Ares Beach, A Coruña, Spain, 1005 miles away from where it was born. A photograph by the observer Antonio Gutierrez is below. The bird was seen at the beach again two days later. What makes this sighting interesting is that very few British ringed Great Black-backed Gulls have been reported in Southern Europe. According to BTO online reports only 3 individuals have previously been recorded in Spain, and 1 in Portugal, although this may not take into account all colour ring sightings. The majority of birds found abroad are in Scandinavian countries.

Thank you very much to Antonio for reporting this sighting. You can see more photographs of T:013 and other colour ringed gulls in North West Spain on his blog -

We have only ringed 16 Great Black-backed Gulls so far in this project. Despite this small number we have had 3 other birds, all from the same catch, seen abroad; 1 in Germany and 2 in Denmark. Such a high return rate from so few birds really demonstrates the value of colour rings on this species.

The majority of gulls we ring in this project are Herring and Lesser Black-backed Gulls. So far this winter we have had lots of interesting sightings from across Europe and beyond, which will be the subject of the next gull post.


Wednesday, 2 January 2013

Tales From Lord Pitsligo’s Cave

The colour ringing of Rock Pipits on the north Aberdeenshire coast has been mainly to study their winter movements, and to discover where they breed. Birds have been trapped on the seaweedy beaches of Pennan, Aberdour, Rosehearty and Cairnbulg. Some birds have been found breeding near to the beaches at Pennan and Aberdour, but no nests have been located at these sites, as yet. The other sites appear to be unsuitable for breeding, but can hold good numbers in the winter.

The high cliffs along the north coast make ideal nesting habitat, but it is far more difficult to locate and reach nests here, than around Girdleness. The presence of breeding seabirds, particularly Herring Gulls, with their incessant alarm calls, further hinders nest-finding attempts. I have annually monitored a stretch of coastline between Aberdour Beach and Rosehearty. There is a rough coastal path, although it is not well used. Occasional colour ringed birds have been found breeding along this stretch, but again, nests remained elusive.

In 2012 monitoring of the stretch began on 14th May. Much of the vegetation along the coast had been grazed hard by sheep, and I wondered if the birds would be able to find enough cover to nest. However, Allan and I managed to find two colour-ringed birds, and both were carrying food: a sure sign they had chicks. The first, Metal/Green Green/Orange, on the territory marked “4” on the map below, was ringed as a first-year, at Rosehearty, in Nov 2011. The other, Metal/Yellow Red/Yellow, with a nest at Lord Pitsligo’s cave, marked “2” on the map, was also ringed at Rosehearty, but was a six-year-old male. Originally metal-ringed in Jan 2007, he was retrapped, again at Rosehearty, in Dec 2009, and his bling added. He has been seen every winter since, at Rosehearty, but had not been recorded during the breeding season, until this year. Had he been missed breeding there during the last two summers, or had he moved territories?

Map showing territories and nests found along the coastline between Aberdour and Rosehearty.

With a huge amount of patience and luck, Allan managed to locate the nest of “Lord Pitsligo”, plus another nest of chicks, marked “1” on the map. Both broods had only recently hatched, so we returned six days later to ring the chicks. Allan then managed to find a third nest with chicks, “3” on the map, that we also ringed. These three nests were very different in their situations: nest 1, a hole near the top of a steeper-than-it-looked-from-the-bottom cliff-face; nest 2, a hole along an almost flat stretch of short grass; nest 3, in a fairly open rock crevice.

 Locations of Nest 1 (May) and Nest 4 (July), possibly 1st & 2nd broods of the same unringed pair. © Allan Perkins

Removing chicks from Nest 2 to ring (May) © Allan Perkins

Nest 3, in an open rock crevice (May) © Allan Perkins

Another interesting feature of these nests was their contents: all contained five healthy chicks, and all are believed to have fledged, though only the brood from nest 3 were all seen (the others remained hidden). Although the nest of the other ringed bird was not found, on territory 4, the pair was seen feeding fledged young (number unknown). Whilst the birds at Girdleness may lay clutches of five eggs, often not all hatch, and very rarely do five survive to fledging there. Nesting success at Girdleness has consistently been 50% over the last three years. Far more nests have been monitored there (31), so it is maybe too early to compare breeding success at the two sites, but it does warrant further study.

The differences in topography and human disturbance at the sites are perhaps responsible for differences in nest survival. The birds on the north coast are noticeably more wary: one bird was observed swallowing a beakful of insects, as soon as it saw us. Only one nest at Girdleness was known to have failed as a direct result of human disturbance, but an abundance of people may encourage predators and scavengers to the area.

Since Lord Pitsligo’s female (at nest 2) was unringed, I decided to try and trap her, as I was interested to see if the pair wintered together. A few days after ringing the chicks, I returned and set some spring traps on the territory. Although I managed to catch two birds, neither was the target female. Firstly, the male of an unringed pair: I had recorded them a few times, hanging around the edge of the territory. I was uncertain whether they had a nest nearby, but they certainly were not feeding chicks. The second bird caught was Lord Pitsligo himself (Metal/Yellow Red/Yellow), trapped for the third time (a record in my study). Like the six-year-old male at Girdleness, he had unmoulted central tail feathers and tertials.

We returned to the area in July, to look for second broods, and saw two pairs feeding young. However, it soon became clear that both pairs were different from those holding the territories earlier in the season. There was no sign of either of the two original colour-ringed birds, or any of the fledged young. An unringed pair now resided on territory 4, previously occupied by Metal/Green Green/Orange. This may have been the pair from nest 1, near the top of the cliff, further along the same beach. At Lord Pitsligo’s Cave (territory 2), the male was colour-ringed, but was the other male caught on the territory, Metal/Red Yellow/Black. Although this nest was not found, it was clear that it was close to the original nest (I did check the original nest and it had not been reused).

Despite the five chicks on territory 4 being quite large when we ringed them, we found that they had been predated by the end of the month: there were chick feathers pulled out underneath the nest. Although partial predation does occur, with some chicks fledging, no chicks from this brood have so far been seen fledged.

Fingers crossed that we’ll manage to find more nests and colour ringed birds there next year. The next Rock Pipit blog will feature the movements of individuals, both local and further afield, including the adventures of Lord Pitsligo’s offspring.