sábado, 14 de agosto de 2021

Gull-billed Tern

Gull-billed Tern (Gelochelidon nilotica)

This is my fourth sighting of Gull-billed Tern (Gelochelidon nilotica) on La Palma, a species whose status on the Canary Islands is open to discussion. The present bird was discovered on July 22 flying over irrigation ponds in Las Martelas (Los Llanos de Aridane), and my three previous records are all from the same area.

The Gull-billed Tern (Gelochelidon nilotica) is not classified as a rarity for the Canaries by the Spanish Rarities Committee, but it is included in the list of 21 Western Palearctic breeding bird species considered by Eduardo García-del-Rey as irregular winter visitors, rare passage migrants, or even true vagrants (see appendix in "Rare Birds of the Canary Islands", Lynx Edicions, 2013)

Below, are the links to my previous records: 

Sept 11 2011

June 21 2013

April 7 2015

Gull-billed Tern (Gelochelidon nilotica) feeding technique.

In the photograph above, the bird's interesting feeding technique can be appreciated. It plucks insects, like dragonflies, from the pond while pattering its feet across the surface at high speed. The legs and feet seem to act as distance-gauges, controlling the low skimming.

Gull-billed Tern Gelochelidon nilotica

This fast-flying individual was difficult to track and photograph in an area like Las Martelas. With a couple of wing-flicks the bird was out of sight, foraging over neighbouring ponds, or scouting further afield. Luckily its erratic movements included a few minutes feeding over one of the larger ponds, where I managed to get the images shown here. 

Gull-billed Tern Gelochelidon nilotica

sábado, 7 de agosto de 2021

Little Ringed Plover second breeding attempt - conclusions

The present post offers a summary of the breeding attempt, evaluates the actions taken, and raises a number of questions.  Click on the following links to follow the whole story:





Chronology of the key events:

May 22: breeding pair first observed in irrigation pond.

May 24-28: courtship and nest preparation.

May 30: nest with 1-2 eggs. Incubation begins.

June 3: nest with at least 3 eggs.

June 4: nest with full clutch of 4 eggs.

June 26: first hatchling observed in the morning.

June 27: first hatchling observed in the morning.

Total of three chicks observed in the afternoon.

July 17: only 2 chicks observed from morning onwards.

July 18: only one chick observed from early morning onwards.

July 23: last remaining chick observed in the late afternoon.

July 24 - 30: unaccompanied adult female observed on July 24, 28 and 29. Thereafter, no birds present.

Conservation measures and threats: 

The Environmental Agency delivered 8 tankerloads of water altogether, on a weekly basis from June 8 onwards. This was undoubtedly a vital contribution to the birds' survival, as no other suitable habitat was available at the time.

An attempt was made to minimise the threat posed by the nearby cat colony. The Environmental Agency negotiated with the relevant animal protection group. The exact number of felines in the colony was unknown, estimates ranging from 6, to as many as 15 individuals. 

Trapping was attempted but encountered legalistic and operational impediments, and only 4 animals were removed from the area. Throughout the chick-rearing period cats were regularly observed in the vicinity, although none actually in the bottom of the reservoir, with the sole exception of the individual photographed on June 3. 

That said, my monitoring was restricted to daylight hours, for periods of up to two hours maximum. The only exception was on July 18 when I stayed at the site until after midnight, without detecting any nocturnal threats to the plovers.

Flight capacity and doubts surrounding dispersal

Wing-exercising, upward propulsion, short glides, and brief low flight within the reservoir are documented in PART 4. At no time did I see any of the chicks try to fly out of the reservoir, or reach the top of the surrounding walls. I was expecting to witness trial flights of some duration/altitude before the birds' final dispersal, but they never materialised in my presence. The last fledgling simply disappeared at an age of 26-27 days.

At no point did I observe friction between the adult female and any of the chicks due to competition for resources. On the contrary, there seemed to be a close bond between parents and offspring throughout the rearing period.

My question is: do Little Ringed Plovers normally disperse in this manner, suddenly abandoning their territory at a given moment, never to return, as soon as they feel strong enough? It strikes me as highly unlikely, but I would appreciate comments from observers with experience of this species.

What happened to the chicks?

Fortunately, I noted down the approximate times of my observation sessions, and digital photographs likewise provide details.

The first chick disappeared sometime between 11:00 July 16 and 09:30 July 17, at an age of 20-21 days.  It could therefore have been taken by either a diurnal, or a nocturnal predator.

The second chick disappeared sometime between 21:40 on July 17 and 07:30 on July 18, at an age of 21-22 days. It almost certainly fell victim to a nocturnal predator.

The third chick disappeared sometime between 20:15 on July 23 and 10:00 on July 24. It could have theoretically been caught by either a diurnal or a nocturnal predator, though the latter seems more likely. Otherwise, it could have voluntarily flown away, never to return, at an age of 26-27 days.

Diurnal predators:

The only realistic candidates are cats and Common Kestrels (Falco tinnunculus). As noted in PART 4, kestrels were frequent around the nesting area. Common Kestrels were formerly held in low regard by henkeepers on the island, as these raptors predated on flightless chicks. 

The adult plovers used a high vantage point on the reservoir rim, or on the roof of an adjacent greenhouse to keep a lookout. Any approaching kestrel was harassed and driven out by one or both of the adult plovers. Despite their efforts, it is possible that the first and third chicks were caught unawares at some point.

Other daytime avian predators such as gulls, corvids, sparrowhawks or Barbary Falcon can almost certainly be discounted for various reasons.

Nocturnal predators:

The most likely candidates are cats, whose presence was more or less constant in the area.

I have never seen Long-eared Owls (Asio otus) in this particular area, but the species is widespread on the island, even in urban surroundings.

Rats are generally believed to shun open areas, such as the exposed beds of irrigation ponds.

Thus, all three chicks could theoretically have been taken by nocturnal predators. As regards the disappearance of the second chick, nocturnal predation is almost certain, while for the third chick, it is more likely than diurnal. The first chick could have been taken either by day or night.

Several key questions unfortunately remain unanswered:

Did any of the chicks, especially the third one, survive and successfully disperse of their own accord?

Is the Common Kestrel (Falco tinnunculus) capable of preying on 20-27 day-old chicks which are already able to run fast and almost fly? 

Do Long-eared Owls (Asio otus) hunt in this area?

viernes, 6 de agosto de 2021

Little Ringed Plover second breeding attempt PART 4

 This is the final part of my account of the second breeding attempt of Little Ringed Plover (Charadrius dubius) on La Palma. In a forthcoming post I will attempt to draw conclusions from this prolonged period of monitoring.

Territorial behaviour by the male plover, July 11. Here, a pair of European Turtle Doves (Streptopelia turtur) are expelled from the feeding area. 

Both male and female plovers defended their territory against avian intruders, which included Berthelot's Pipit (Anthus berthelotti) and Grey Wagtail (Motacilla cinerea), in addition to the European Turtle Dove (Streptopelia turtur) shown above. 

The three chicks plus parent foraging in the wet sand, July 11

The weekly water delivery evaporated after about 5 days, with damp sand remaining until the next tankerload arrived.

Flight feathers and the characteristic yellow eye-ring developed rapidly in the young birds

All three chicks together, with the larger, first-born on the right. At this point in time (July 11) they are 14-15 days old.

Flight development

I was particularly interested in monitoring flight development, as it seemed inevitable that the brood of three chicks would eventually disperse. Backtracking a little, the chick shown raising its wings in the following image was just over one week old:

Wing-raising and flight-muscle stretching, July 5

Early wing exercises, July 11

After wing raising, the next stage was jumping upwards, July 11.

The learning process continues, July 16.

Briefly airborne on July 16.

More wing-beating, July 16. Here, the chicks are 19-20 days old.

More flight practice from July 16

Just when everything seemed to be going smoothly, an unexpected turn of events occurred. On the morning of July 17 I found only two chicks, plus the two adult plovers. Predation could have taken place either during the night, or early the same morning, prior to my arrival at the site at about 09:30. The two adult birds were both present, and the male seemed to be distressed, suggesting that the attack was recent.

I returned in the evening and stayed until 21:40, partly to confirm that one of the chicks was indeed missing, partly to rule out daytime predation by kestrels.

At 07:30 on the following morning, July 18, only a single chick remained. Predation by cats or some other nocturnal predator seems the only explanation for this second disappearance. The matter will be dealt with in an upcoming epilogue.

The last time I saw all three chicks together was July 16. I did not photograph them on that date, but below is a picture from July 15:

All three chicks together in their rest area on July 15.

From roughly mid-July I observed Common Kestrels (Falco tinnunculus) in the vicinity with increasing frequency. The raptors would perch on the upper rim of the reservoir, or in the branches of tall Agave plants overlooking the plovers' feeding area. The kestrels' low, swooping flights usually ended with the adult plovers driving out the unwanted visitors. But how successful the raptors' hunting was during my absence is not known.

Common Kestrel (Falco tinnunculus) perched on the upper rim of the irrigation pond, July 16.

The adult plovers kept a close lookout for Kestrels (Falco tinnunculus), sounding the alarm from their vantage point on the highest part of the reservoir rim whenever danger threatened.

One of the two remaining chicks getting slightly higher above the ground on July 17.

Finally, I witnessed true flight on July 21. In the images above and below, the single surviving chick is captured flying about half a metre above ground-level over a distance of not more than 10 metres.

Low flight of the surviving chick on July 21. Here, the bird was 25-26 days old.

I last observed this immature bird at about 20:15 on July 23, by which time it was 26-27 days old. The following morning, July 24, it had gone. The adult female plover was still present and was seen intermittently for another few days, but by July 30 she had also left.

Thus, the second breeding attempt of Little Ringed Plover (Charadrius dubius) on La Palma came to an inconclusive end.
None of the newborn plovers have been seen at the breeding site or elsewhere in the vicinity since July 23. It is not clear whether the last-surviving chick became fully independent and successfully dispersed, or whether it unfortunately fell victim to daytime or nocturnal predators. 

lunes, 2 de agosto de 2021

Little Ringed Plover second breeding attempt PART 3

One of the conservation measures implemented by the Environment Agency of La Palma was regular delivery of untreated water. Altogether, 8 tankerloads were pumped into the reservoir on a weekly basis. Below are three shots of the operation on June 16:

Hosepipe in place...

Pumping begins...

The two plovers at the edge of the newly-created pool.

Incubation continued throughout the rest of June, until finally, on June 26, the first chick hatched:

Little Ringed Plover (Charadius dubius) with recently-hatched chick, Jun 26

With the first chick nearby, the female plover continues to incubate the remaining eggs.

Female plover incubating the rest of the clutch, June 26.

Two more chicks hatched on the following day, June 27. Of the original four eggs, only one failed.

The hatchlings made steady progress, initially foraging around the muddy edges of the water, then later exploring the drier parts of the reservoir bottom.

The full brood of three Little Ringed Plover (Charadrius dubius) chicks, June 28.

June 28

Parent with one of the chicks, June 28.

With every day that passed, there was increased hope that this second breeding attempt would succeed. The hatchlings from the first ill-fated attempt had survived only a couple of days, whereas the second brood of 3 chicks was still going strong after two weeks. The following photos were taken between June 29 and July 7:

One of the chicks half-swimming, half-wading across the pool, June 29.

All three chicks in one of the drier areas, June 29.

Parents and offspring together on July 4.

Exploring another part of the dry reservoir bed, July 5.

The three chicks in their daytime resting area, July 9.

domingo, 1 de agosto de 2021

Little Ringed Plover second breeding attempt PART 2

Site of nest, at far end of pond

The pair of Little Ringed Plover (Charadrius dubius) chose a nesting site very close to the access steps. The following image shows one of the birds incubating:

Little Ringed Plover nesting site

Egg-laying started at the end of May, with both male and female taking part in incubation. Here, the male settles down for a spell:

Little Ringed Plover (Charadrius dubius) at nest

Little Ringed Plover (Charadrius dubius) incubating

Everything seemed to be going according to plan, until one day I photographed a ginger cat hunting a mouse very close to the plovers' nest. The male plover surprisingly held his ground, only getting up when the cat lunged towards him. Once the cat moved away again, the bird calmly returned to the nest, which is visible in the lower right hand corner of the following images:

Feral cats were obviously going to cause problems, so I contacted the Environmental Agency who promptly made some enquiries. It turned out that there was a cat colony in the area, an unknown number of stray cats which had initially been trapped, neutered and released by volunteers from a local animal protection group. The feeding station was just outside the irrigation pond in which the plovers were nesting. 

Over the next few days I spotted various other felines in the vicinity, though none in the bottom of the empty reservoir. Nevertheless, something had to be done if the plovers' second breeding attempt was to prosper.

Negotiations between the environmental agents and the animal group led to about four cats being trapped or captured by volunteers, and relocated to other colonies. Several other animals were left still roaming the area, however.

Other potential threats facing the breeding plovers included harassment or predation by stray or free-roaming dogs; inadvertent disturbance or damage to the eggs caused by people transiting through the nesting area; resident avian predators, of which more later.

As a protection measure against dogs and people, the environmental agency eventually placed a barrier across the steps inside the reservoir, impeding access to the bottom. Signage warning of nesting birds was considered unwise, given that it might attract unwanted attention to the location. 

sábado, 31 de julio de 2021

Little Ringed Plover second breeding attempt, PART 1

Shortly after their first, unsuccessful breeding attempt, the pair of Little Ringed Plover (Charadrius dubius) moved to another dried-out irrigation pond in Las Martelas (Los Llanos de Aridane).

Here is the post describing their first attempt, and below is a photograph of the new breeding site:

This second location is very similar to the first one. In both cases these are abandoned irrigation ponds in which small amounts of rainwater accumulate. A tiny puddle is just visible at the far end, and a layer of sand in the central area.

These ponds are privately owned but are freely accessible. Some have been converted into lorry parks, workshops, or even skateboard parks. Most, like the pond chosen by the pair of Little Ringed Plover (Charadrius dubius) have simply fallen into disuse, with no wildlife conservation laws to protect them.

Pair of Little Ringed Plover (Charadrius dubius)

The female is slightly larger, generally paler in colour, with less white above the eye.

I first observed the breeding pair in their new location on May 22. The images above date from May 27. By the end of May there were already 1-2 eggs in the nest, and on June 4, I photographed the full clutch of 4, visible in the centre of the following image:

I have deliberately left this image uncropped, to give a better idea of how well camouflaged the eggs are.

Both birds took turns incubating and defending the nest. Below is a picture of the female, taken on June 4:

Female Little Ringed Plover (Charadrius dubius)  sitting on the nest