Latvian WtE nest webcamera Juras-erglis: Discussions

White-tailed eagles in Latvia

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Re: Latvian WtE nest webcamera Juras-erglis: Discussions

Post by ame »

The events in the spring 2021


Introduction

Raimis went missing after March 27, and Milda was left alone with three eggs to incubate. She wasn't alone long though: a series of male eagles turned up and visited her in a row. Their purpose seemed to be to take over the territory and the nest although it was still clearly occupied by Milda. It was surprising how quickly the news about a vacancy in the territory seemed to spread in the forest. It was as if the disappearance of Raimis had been announced in the first issue of Eagle Times of Kurzeme after he was gone. The first visitor came already in the next evening, only about 24 hours after Raimis had left for the last time.

It seems now that Milda has established a relationship with a new partner who still has not received a 'proper' name from the DDF. He has been called Mr L in the Looduskalender forum (LKF in short) and in Dabasdati forum (DDF) K Kungs (meaning Mr K; I don't know what the letter K stands for.) The letter L refers to Mr L's Left Leg which was injured first when he arrived. The chain of events which led to Mr L staying was messy and hectic, involving a series of males trying to win the Kingdom and the Queen's hand. During the process we also saw things which were quite unprecedented and surprising even to ornithologists.

I have reviewed the data in order to find out as much as possible of what really happened during the spring. I also wanted to find out who were involved, i.e. the identification of the eagle visitors was my goal, too. My motivation has been my interest in how the white-tailed sea eagles choose their partners (I might also say it's simply my curiosity). The choice of the spouse is one of the most significant choices the eagles make in their lives because they form life-long couples. Their breeding success must depend to some extent on the "goodness" of the partner. We saw this spring that the death of a spouse can be quickly followed by finding a new mate. On previous times we have seen that this doesn't always happen. Robert wasn't interested in any young females after Durbe disappeared. He gave up his territory and left. Vents made the same choice after Šilutė disappeared in the end of 2016.

In the following I shall first give summaries of the daily events with links to the corresponding pages in the Observation thread. I have also made some new pictures to clarify the events. Some of the new pictures i have added in my posts in the Observation thread (if there was enough space). I shall also give some pictures of the eagles' tails and profiles.

Next I shall summarize the events and make a list of both the identified eagles and the questions which remained unanswered. In the end I shall discuss the findings and try to draw some conclusions. The list of events is long. If someone thinks that it is boring or useless or non-interesting then one can skip reading it.
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Post by ame »

Making observations with the nest camera

We can see only a small fraction of the space around the nest tree. Urmas Sellis has said that watching a nest camera is like looking through a keyhole. I think that our view with the Durbe camera is slightly larger: it's rather like looking through a mail slot.
https://ak.picdn.net/shutterstock/video ... umb/11.jpg

The width of our viewing angle is 107 degrees (slightly wider than a straight angle). The camera looks a few degrees west of south-west so that we see the sunrise in the left upper corner of the picture in the spring and autumn. The Sun shines at noon near the top right corner in the horizontal direction, either in or out of the picture, depending on the time of the year. In springs and autumns the path of the Sun is low near the horizon and blinds our view badly in the mornings if it's not cloudy.

The nest covers almost half in the front of the picture. However the scenery behind the nest is much wider with a lot more free airspace than in most other nest cameras because the camera is not very much tilted downwards and there is a lot of open space around the nest tree, at least in the direction where the camera is pointed to. Behind the nest we see forest in the background and some more open lowland with smaller trees and bushes. At times this area is clearly partially covered with water. We call this area 'the meadow', although it could be called 'the swamp' as well.

The horizon is curved, probably mostly due to the distortion caused by the camera optics. There may also be some some real curvature in the horizon in the lateral direction. The forest in the back is probably on a hillside rising in the longitudinal orientation (along the line of sight). Above the skyline formed by the treetops we see a narrow slice of the sky, wider in the edges than in the centre. Above the meadow we can see a lot more open airspace than in any other camera. This allows us to see a lot of birds' traffic in the air, too. Nevertheless our view is very limited. Most of the eagles' lives take place outside our view and we can only guess what is happening. Some more information can be gained by listening to the sounds and the voices of the eagles.

Often eagles may give a somewhat phlegmatic impression in their nest life if there is nothing or no-one disturbing them. They just stand on the nest or sit on branches for minutes, sometimes even for hours. They do, however, always keep a keen eye on their surroundings (unless they simply sleep), and they are capable of instantaneous and incredibly swift action if that is required. Most of the claw-to-claw fights which we have seen in the camera view have happened very quickly, usually within a second or two, sometimes even faster. Chases take naturally longer times but they happen mostly outside our view. Only the voices of eagles can tell us that a chase or a fight was on. One of the fights this spring led to the fighters dropping down from the tree together and we could hear that a fight with physical engagement went on under the nest for some time.

The camera takes 25 frames in a second (one picture per 0.04 seconds, in other units per 40 milliseconds). That is sometimes not nearly enough to see what happened. Some eagle attacks which we have seen at this nest have recorded only one or two frames. The swiftness of events makes it very difficult to make accurate observations when viewing live action. Even more difficult is to write down what you saw (or of what you think that you saw) at the same time. The data has to be reviewed later with good time to see everything that can be found. The videos of the events are indispensable in finding out what happened. Often videos need to be analysed frame by frame. Sometimes even that is not enough for example due to bad lighting conditions and a lot remains unsolved.

- - - - - - - - - - - - - - -
If your wish skip over the daily observations go here:
https://www.looduskalender.ee/forum/vie ... 59#p836059
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Post by ame »

Observations of the daily events after Raimis disappeared.

March 27
19:42 Raimis left the nest for the last time.
https://www.looduskalender.ee/forum/vie ... 53#p784553

March 28
20:08 a stranger with Latvian ring visited. the eagle said nothing and stayed on the top branch.
https://www.looduskalender.ee/forum/vie ... 15#p784715

March 29

7:05 two eagle voices from the forest, first a male, joined a few seconds later by another voice, probably a female.
7:06 again two voices, 7:06:48 a female voice, too.
https://www.looduskalender.ee/forum/vie ... 58#p784758
8:21 a male visited.
8:33 a Latvian male visited.
8:42 two eagles fly away very close to each other (together or chasing each other).
after this the Latvian male was not seen again.

9:01 a strange unringed male began to make visits. Mr X.
the tail was quite white like the tail of Raimis and the spots were much smaller, like Milda's spots, but this eagle has the same dark "rays" as Raimis in the border between the white tail and the dark back.
Image
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Post by ame »

March 30
6:38 the strange male Mr X comes for the first visit.
(as usual i don't want to postulate any more eagles than are necessary to explain the events. according to this principle i assume that the stranger was the same as in the previous day unless something else is proven later).
https://www.looduskalender.ee/forum/vie ... 93#p784993

16:51 the stranger Mr X made a blitz attack on the nest.
small spots like in Milda's tail but the borderline between the back and tail is broken, not smooth like Milda's. no ring.
the tail pattern seems to be similar enough with the tail on the previous day.
Image
https://www.looduskalender.ee/forum/vie ... 54#p785154

19:53 - 20:00 the last visit of the stranger (invisible on the top).
https://www.looduskalender.ee/forum/vie ... 10#p785210
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Post by ame »

March 31

6:13 the strange male calls nearby in almost dark.
https://www.looduskalender.ee/forum/vie ... 57#p785257
6:34 flies by.
7:01 flies to top to make the first visit of the day.

13:33 the strange male flies to the nest, followed by Milda to the top branch.
https://www.looduskalender.ee/forum/vie ... 75#p785375

the right wing profile of Mr X.
Image

the left wing profile of Mr X.
Image

two small spots on the tail like in Milda's tail. short rays on the borderline between the dark back and the white tail, but also some long and thin rays.
the tail pattern is consistent with the patters of the tail on previous visits when they were visible.
Image
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Post by ame »

March 31
continued

13:51 another visit to the nest.
https://www.looduskalender.ee/forum/vie ... 82#p785382

17:15 Mr X made another visit to the nest. the tail spots weren't so small after all. about the same size as Milda's.
Image

left wing of Mr X.
Image

right wing (and the mouth) of Mr X.
Image

after that visits to the top and to the top branch.
20:10 leaves for the day.
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Post by ame »

April1

6:39 the stranger Mr X visits top.
https://www.looduskalender.ee/forum/vie ... 20#p785620

after that many visits.
11:24 to the right branch but mostly out of sight.
https://www.looduskalender.ee/forum/vie ... 00#p785700

12:36 an event involving possibly two eagles and Milda.
https://www.looduskalender.ee/forum/vie ... 29#p785729
two eagles were not visible at the same time (not counting Milda), but
12:41:31 male called on the top and another eagle was visible in the top left corner flying away. a few seconds later the male flew from the top to approximately the same direction as the first eagle.
https://www.looduskalender.ee/forum/vie ... 34#p785734

14:03 Mr X made a visit on the nest.
https://www.looduskalender.ee/forum/vie ... 58#p785758

the left wing of Mr X.
Image

the tail of Mr X.
Image

18:22 again a nest visit by Mr X.
https://www.looduskalender.ee/forum/vie ... 65#p785865
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Post by ame »

April 2

6:21 Mr X arrived to the top branch for the first time.
https://www.looduskalender.ee/forum/vie ... 12#p785912

the left wing of Mr X.
Image

the right wing of Mr X.
Image

the tail of Mr X.
Image
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Post by ame »

Apr 2
continued.

14:51 - 14:54 a young eagle (3rd CY male?) visited.
https://www.looduskalender.ee/forum/vie ... 99#p786099

the name Mr X for the first time.
ame wrote: April 2nd, 2021, 3:26 pm 15:25 both back. first i thought that Milda was first but no. this is the tail of Mr X.
Image
...
https://www.looduskalender.ee/forum/vie ... 22#p786122
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Post by ame »

Apr 3

6:09 a male flew to the top branch. Mr X probably. it was still too dark to see anything.
6:43 he flew away.
https://www.looduskalender.ee/forum/vie ... 60#p786360

15:41 Milda flew out.
https://www.looduskalender.ee/forum/vie ... 64#p786464
16:15 she returned.
she also made some other short outings during the day. (she was probably looking for Raimis.)

no other visits by strangers, only the morning visit.
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Post by ame »

Apr 4

10:45 Milda flew out.
https://www.looduskalender.ee/forum/vie ... 22#p786622

11:38 human voices under/near the nest.
https://www.looduskalender.ee/forum/vie ... 39#p786639

16:24 Milda returned after being away for 5 h 39 min. she had eaten well. she had eaten on March 27 the previous time so this was the 8th day after Raimis disappeared.

a male followed Milda. the tail of the male (or him altogether) was not well seen but it reminded the tail of Mr X.
https://www.looduskalender.ee/forum/vie ... 32#p786732
the male tried to land on the nest twice after this, but he or his tail was not seen properly.
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Post by ame »

Apr 5

6:15 - 6:18 a male with normal voice visited the nest. it was still too dark to see much anything, only that the tail was mostly white.
https://www.looduskalender.ee/forum/vie ... 70#p786870

9:54 a new male came for a visit: Mr Z.
https://www.looduskalender.ee/forum/vie ... 10#p786910

the tails are different like day and night. Mr X has a Milda-type tail with small spots and no rays. Mr Z has Raimis-type tail with big spots and big rays.
i also think that the male who came home in the previous afternoon was Mr X, and not this new male Mr Z, although it is of course possible.
Image

12:57:57 a third eagle besides Mr Z and Milda flew over the nest, then by over the meadow and turned to the right.
Image

then the eagle who flew by called in the forest with a male's voice (maybe started with a chip-chip).
after this the third eagle was heard calling in the forest several times.
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Post by ame »

Apr 5
continued

15:32 a strange male (Mr X?) flew around the nest tree and stayed on the spruce on the right. Mr Z came to the nest twice.
https://www.looduskalender.ee/forum/vie ... 38#p787038

16:22 - 16:27 another event involving two strange males and Milda. one of the strangers was Mr Z. the males were competing for the ownership of the nest, and Milda on the nest with eggs was not important for them. she was only an irrelevant bystander in the process. from Milda's point of view both males were intruders who were disturbing her life.
https://www.looduskalender.ee/forum/vie ... 66#p787066

16:50 a male (with normal voice) visited the top. soon an eagle landed there and
16:51 Mr Z jumped on the nest from the top. big spots and long wide "rays" on the border between the back and the tail.
Image
https://www.looduskalender.ee/forum/vie ... 86#p787086

17:18 Mr Z on the nest again and another male outside.
https://www.looduskalender.ee/forum/vie ... 04#p787104
17:21 two strangers flew away over the meadow. Milda was on the top branch.
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Post by ame »

Apr 5
continued

18:35 an attack on Mr Z on the top branch. Milda waved her wings on the nest.
Image

then the eagle in flight knocked Mr Z off the branch and both dropped down. then the two strange males fought down under the tree making scary voices for a long time.
18:54 the fight sounds ended. - it never became clear who the other fighter was.
https://www.looduskalender.ee/forum/vie ... 31#p787131

19:25 a male flew to the top branch.
https://www.looduskalender.ee/forum/vie ... 52#p787152
the male stayed on the branch and didn't give a good picture of his tail (or much anything else either).
21:06 the male flew away. it was almost dark. it's unclear who this male was.
https://www.looduskalender.ee/forum/vie ... 81#p787181

Mr Z was wet all day because the weather was so bad so. it was not possible to get decent pictures of his wings. only his tail was well visible.
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Post by ame »

Apr 6

5:40 a stranger flew to the top branch already at the crack of dawn.
https://www.looduskalender.ee/forum/vie ... 19#p787219

7:46 the stranger flew away over the meadow. the tail spots looked smaller than the spots of Mr Z.
during his visit the male called a few with normal voice.
Image

10:54 a stranger flew to the nest. first he called with funny chip-chip-chip- voice like Mr C alias Chips did later. after Milda had chased him away he called with a normal voice in the forest.
the best frames of the tail. the tail looks "cleaner" than the tail in the above picture which shows Mr Z.
Image
https://www.looduskalender.ee/forum/vie ... 78#p787278

11:12 a male with normal voice called in the forest.
https://www.looduskalender.ee/forum/vie ... 87#p787287

11:21 -11:29 a male with normal voice visited.

12:08 Milda flew out.
https://www.looduskalender.ee/forum/vie ... 03#p787303
13:11 she returned. she didn't have a big crop but she perhaps had eaten something though.
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Post by ame »

Apr 6
continued.

15:49 a male with normal voice called nearby.
https://www.looduskalender.ee/forum/vie ... 67#p787367

16:22 a male with normal voice called nearby.

17:22 Milda flew out.
17:23 - 17:26 a strange male visited.
https://www.looduskalender.ee/forum/vie ... 06#p787406
this eagle was first mistaken as Milda but the tail was different. the spots in the centre of the tail seem to be small (although difficult to see properly). the tail has "rays" on the side. Milda does not have these.
this eagle didn't say anything. he rolled the eggs.
Image
balistar wrote: April 6th, 2021, 8:15 pm another two pics for comparison, almost in same position, but not in the same distance to the cam
...
17.22.10 Milda
Image

17.23.41 the other eagle ...
Image
the outer feathers on the wings are clearly different so the visitor was not Milda.
also i thought first that this stranger was a female because the beak was not very small and the ankles were not very thin compared to Milda.

17:51 Milda returned.

18:59 a male with normal voice flew to the top branch.
https://www.looduskalender.ee/forum/vie ... 49#p787449
20:27 the male flew away.
https://www.looduskalender.ee/forum/vie ... 76#p787476

it is possible (perhaps even likely) that the eagle in the morning was Mr Z. he behaved in the same way as Mr Z on the previous day: called wildly every time when he flew to the nest tree and tried to land right away on the nest and got kicked out by Milda.

the eagle in the afternoon was perhaps the eagle who was fighting with Mr Z on the previous day. on the egg-rolling visit in the late afternoon the eagle didn't show his tail, but he seemed to have a normal beak. the stranger who was here all day sometimes called with a chip-chip-voice, but he seemed to have a normal beak (the 10:54 visit, which was probably Mr Z anyway).
the last visit in the evening was probably by the same eagle who visited at 17:23-26. he stayed on the top branch and didn't make much noise.

on the whole the eagle/eagles who were seen at the nest on Apr 6 remain unidentified.
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Post by ame »

Apr 7

5.52 a strange male with normal voice called in the forest.
https://www.looduskalender.ee/forum/vie ... 21#p787521

6:24 again a strange male with normal voice called in the forest.

6:47 a strange male flew to the top and began his call with a chip-chip-chip. then the voice changed to normal.
https://www.looduskalender.ee/forum/vie ... 25#p787525

10:18 a stranger flew to the spruce nearby.
https://www.looduskalender.ee/forum/vie ... 77#p787577
11:22 the stranger called in a normal voice.
11:23 he flew to the top branch and began his call with a chip-chip-chip. then the voice changed to normal.
https://www.looduskalender.ee/forum/vie ... 99#p787599
Milda flew out and the stranger came down to the nest. the tail looked amazingly similar to Milda's tail: small centre spots and big round feather tips on the borderline of dark and white, but also dark rays.
Image

Image

this eagle was most probably not Mr Z because he used to be much more intrusive and fly straight to the nest. Mr Z also didn't ever call in the chip-chip-chip-voice either. maybe i may call this strange eagle Mr W. (the letter Y was used for the hypothetical girlfriend Miss Y who never materialized.)

this eagle could not be Mr C yet although at times he called chip-chip-chip, too. Mr W also had a normal beak.
Image
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Post by ame »

this is the tail of Mr X. two little spots in the centre like Milda's, the broken / uneven border between the dark and white unlike Milda's tail. short rays and thin along the whole borderline.
Image

the tail of the eagle who visited on Apr 6 at 17:23 and quietly rolled the eggs. two little spots as well but the rays are different. here fewer but thicker and longer rays than in the tail of Mr X.

the tail of Mr W.
Image

the tail of Mr Z had much more black in the centre spots and much broader and longer rays.
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Post by ame »

not only the tail but also the right wings are clearly different.
Mr X
Image

the eagle who visited on Apr 6 at 17:23 and quietly rolled the eggs. this eagle was probably Mr W on his first visit.
Image

unfortunately it was not possible to get pictures of the profiles of Mr Z.
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Post by ame »

Apr 7
continued

it was very difficult to get comparable pictures of the eagle on Apr 7 and Mr W on Apr 8.
the tails. both showed similar interest in the eggs.
Image

the profiles. i think that it is (very?) probable that this was the same eagle.
Image

19:50 onward Mr W began to visit the nest tree more frequently and seemed to be alarmed.
https://www.looduskalender.ee/forum/vie ... 18#p787818

20:47:10 a third eagle flew by.
https://www.looduskalender.ee/forum/vie ... 42#p787842

21:19 Mr W stayed on the top branch till dark. another eagle was heard calling outside with a strange chip-chip-voice.
https://www.looduskalender.ee/forum/vie ... 64#p787864
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