|
adult: August
adults in the colony
In the Maasvlakte colony many adults try to raise two juveniles. As soon as the fledglings can move, the family tries to find a more comfortable place outside the colony, often at the beach or the near fresh water lakes. By the end of August, 99% of the adult LBBG from the Maasvlakte and their juveniles (approximately 70.000 birds) have left the Maasvlakte and start migrating south (at least leave the immediate feeding grounds around the colony). For a while, they gather at the beach, in mixed groups of different age-classes.
Several 1.000s of LBBG can be present up to mid September. In these groups the races graellsii and intermedius are both present, but hard evidence to categorize adults to certain races is very difficult, and classification is often only possible when birds are banded / ringed. From mid-October numbers of LBBG decrease rapidly.
moult in the primaries
August is normally a month when primary moult is easy to detect, even on adult birds with folded wings. A small survey of adults in the Maasvlakte colony did not point to a significant primary moult delay in adults with begging youngs in the colony. Individual variation in adult LBBG within a certain colony seems to be at least as large as primary moult variation between colonies of Dutch intergrades and presumed intermedius from Scandinavia. In the table below, remaining old primaries are plotted for mixed groups graellsii, Dutch intergrades and intermedius at the Maasvlakte in the second half of August. Probably, most birds originate from the nearby colony and are Dutch intergrades, but large groups of Scandinavian birds arrive from mid-August onwards.
Intermedius LBBG from Denmark and southern Norway (intermedius) probably arrive later on the breeding grounds in spring, compared to Dutch intergrades. Subsequently, it may be expected that egg-laying date is later in these populations. It remains to be seen whether or not they show delay in primary moult stage. Such surveys should only involve ringed (certain origin) adults. At this moment, such surveys are impossible; comparable analyses are unreliable by lack of sufficient ring observations.
So far, the hypothesis that intermedius have delay in primary moult could not be verified, but if it's true, the average remaining old primary figure in the table is overestimated (if read as applying to Dutch intergrades) by the input of intermedius arriving in August and later on. On the other hand, it is expected that Dutch intergrades with low moult score (arrested or suspended moult) are keen to leave the Netherlands as soon as possible, leaving a group of adults with relatively high moult score. At this moment, the figures in the table can be used as indication for "what average moult stage can be expected in the second half of August in LBBGs of various origins, present in the Netherlands".
Tables & Graph
| starting date:
|
30 Jul |
06 Aug |
13 Aug |
20 Aug |
27 Aug |
03 Sep |
| week no:
|
31
|
32
|
33
|
34
|
35
|
36
|
| REM 0
|
0
|
0
|
0
|
0
|
0
|
0
|
| REM 1
|
0
|
0
|
0
|
0
|
0
|
0
|
| REM 2
|
0
|
0
|
0
|
1
|
3
|
4
|
| REM 3
|
0
|
0
|
2
|
6
|
66
|
25
|
| REM 4
|
4
|
0
|
24
|
121
|
187
|
24
|
| REM 5
|
7
|
1
|
46
|
203
|
182
|
4
|
| REM 6
|
13
|
12
|
38
|
89
|
105
|
0
|
| REM 7
|
16
|
6
|
23
|
65
|
33
|
0
|
| REM 8
|
13
|
3
|
23
|
31
|
25
|
0
|
| REM 9
|
1
|
3
|
9
|
15
|
15
|
0
|
| REM 10
|
10
|
1
|
6
|
15
|
14
|
0
|
|
|
0
|
|
|
0
|
0
|
0
|
| n =
|
64
|
26
|
171
|
546
|
630
|
57
|
| average P =
|
7.1
|
6.9
|
6.1
|
5.6
|
5.1
|
3.5
|
| 95% CID =
|
0.43
|
0.51
|
0.25
|
0.13
|
0.12
|
0.19
|
| inverse =
|
2.00
|
2.06
|
1.97
|
1.96
|
1.96
|
2.00
|
| Variantie (s2) =
|
2.91
|
1.59
|
2.65
|
2.24
|
2.43
|
0.54
|
| SD (s) =
|
1.71
|
1.26
|
1.63
|
1.50
|
1.56
|
0.73
|
| SE (sx) =
|
0.21
|
0.25
|
0.12
|
0.06
|
0.06
|
0.10
|
|
|
|
|
|
|
|
|
| % class:
|
|
|
|
|
|
|
| 0
|
0
|
0
|
0
|
0
|
0
|
0
|
| 1
|
0
|
0
|
0
|
0
|
0
|
0
|
| 2
|
0
|
0
|
0
|
0
|
0
|
7
|
| 3
|
0
|
0
|
1
|
1
|
10
|
44
|
| 4
|
6
|
0
|
14
|
22
|
30
|
42
|
| 5
|
11
|
4
|
27
|
37
|
29
|
7
|
| 6
|
20
|
46
|
22
|
16
|
17
|
0
|
| 7
|
25
|
23
|
13
|
12
|
5
|
0
|
| 8
|
20
|
12
|
13
|
6
|
4
|
0
|
| 9
|
2
|
12
|
5
|
3
|
2
|
0
|
| 10
|
16
|
4
|
4
|
3
|
2
|
0
|
|
|
|
|
|
|
|
|
|
% control: |
100
|
100
|
100
|
100
|
100
|
100
|
Table above, data for the Netherlands (2000-2010), results for August (aggregated week): number of remaining old primaries in adults.
REM10 = 10 primaries still old (hence, complete moult not started yet).
Above: Scatter Plot for PMS in adult Lesser Black-backed Gulls. Number of remaining old primaries throughout the year (arrested moult excluded). Sample size is 6.171 birds.
Above: Scatter Plot for PMS in adult Lesser Black-backed Gulls. Number of remaining old primaries for August (arrested moult excluded). Sample size for this graph is 357 ringed birds + 1137 unringed birds.
|
starting date:
|
09 Jul
|
13 Aug
|
20-Aug
|
27-Aug
|
10 Sep
|
|
week no:
|
28
|
33
|
34
|
35
|
37
|
|
NEW 0
|
115
|
3
|
2
|
1
|
0
|
|
NEW P1
|
6
|
2
|
4
|
0
|
0
|
|
NEW P2
|
0
|
6
|
7
|
2
|
0
|
|
NEW P3
|
0
|
7
|
10
|
12
|
0
|
|
NEW P4
|
0
|
8
|
1
|
25
|
6
|
|
NEW P5
|
0
|
1
|
1
|
5
|
13
|
|
NEW P6
|
0
|
0
|
1
|
0
|
11
|
|
NEW P7
|
0
|
0
|
0
|
0
|
3
|
|
NEW P8
|
0
|
0
|
0
|
0
|
0
|
|
NEW P9
|
0
|
0
|
0
|
0
|
0
|
|
NEW P10
|
|
|
|
|
|
|
|
|
|
|
|
|
|
n =
|
121
|
27
|
26
|
45
|
33
|
|
average NEW P =
|
0.0
|
2.7
|
2.4
|
3.7
|
5.3
|
|
95% CID =
|
0.04
|
0.55
|
0.55
|
0.27
|
0.32
|
|
inverse =
|
1.98
|
2.06
|
2.06
|
2.02
|
2.04
|
|
Variantie (s2) =
|
0.05
|
1.92
|
1.85
|
0.82
|
0.79
|
|
SD (s) =
|
0.22
|
1.39
|
1.36
|
0.90
|
0.89
|
|
SE (sx) =
|
0.02
|
0.27
|
0.27
|
0.13
|
0.15
|
|
|
|
|
|
|
|
|
% class
|
|
|
|
|
|
|
0
|
95
|
11
|
8
|
2
|
0
|
|
1
|
5
|
7
|
15
|
0
|
0
|
|
2
|
0
|
22
|
27
|
4
|
0
|
|
3
|
0
|
26
|
38
|
27
|
0
|
|
4
|
0
|
30
|
4
|
56
|
18
|
|
5
|
0
|
4
|
4
|
11
|
39
|
|
6
|
0
|
0
|
4
|
0
|
33
|
|
7
|
0
|
0
|
0
|
0
|
9
|
|
8
|
0
|
0
|
0
|
0
|
0
|
|
9
|
0
|
0
|
0
|
0
|
0
|
|
10
|
0
|
0
|
0
|
0
|
0
|
|
|
|
|
|
|
|
|
% control:
|
100
|
100
|
100
|
100
|
100
|
Table above, data for the Netherlands (2000-2010), results for August (aggregated week): number of new, fully grown primaries in adults.
NEW0 = no new primaries visible (arrested moult excluded in this analysis). So either P1 still old, or P1 dropped, but the very tip still not visible.
NEW1 = P1 longest new primary. Range between "at least the tip of P1 is visible" until "tip of P2 still shorter than P1".
NEW2 = P2 longest new primary. NEW3 = etc.
Above: Scatter Plot for PMS in adult Lesser Black-backed Gulls throughout the year. Longest new primary is classified "fully grown". Sample size is 2.969 birds. Birds scored on NEW primaries (arrested moult excluded).
Above: Scatter Plot for PMS in adult Lesser Black-backed Gulls. Scoring on longest new primary, which is classified "fully grown" for August (arrested moult excluded). Sample size for this graph is 98 ringed birds.
The earliest date for birds with missing primaries is 30 April 2006, which is not the earliest day in our complete sample. We scored 98 Lesser Black-backed Gulls prior to that date, some already in February. As can be expected, none of these was in primary moult, and this group was excluded in our further analysis as it will only result in a misfit for the onset of moult, using linear regression statistics.
The last scoring days were in November, with a larger sample (133 adults) on 04 November 2010. From that date we have the last birds with retaining old primaries (13 birds with 1, 2 or even 3 old primaries; 120 birds with no old primaries left). From other days in November, only 10 birds were scored (all ringed adults). They all had no old primaries left.
The first tine a new primary (P1) was visible, was on 08 May 2006. Prior to this date, birds were scored missing inner primaries, but the very tip was still not visible (and therefore not scored). As soon as the tip of P1 was visible, this was automatically scored "fully grown" For the other primaries to be scored fully grown, they had to exceed the previous primary in length (so P2 fully grown, only from when it is longer than P1).
Peter Stewart presents onset of primary
moult by scores for caught adult Lesser Black-backed Gulls in the Severn Estuary,
U.K., repeated in the table below.
To read his results, see this PDF file.
|
Table: the number of old remaining primaries present. Compare PMS of adult graellsii at half monthly intervals. Data from the Severn Estuary Gull Group by Peter Stewart: The primary moult of the Lesser Black-backed Gull (special publication No 1). Scores in the Netherlands can be influenced by unringed nominate fuscus, in autumn in particular.
|
|
|
Netherlands
|
Severn
Estuary
U.K.
|
|
|
PMS range
|
N:
|
Average PMS
|
PMS range
|
N:
|
Average PMS
|
|
1-15 apr
|
10
|
49
|
10
|
8-10
|
216
|
9,9
|
|
16-30 apr
|
10
|
47
|
10
|
10
|
197
|
10,0
|
|
1-15 may
|
8-10
|
849
|
9,8
|
8-10
|
167
|
9,9
|
|
16-31 may
|
7-10
|
380
|
9,7
|
7-10
|
76
|
9,5
|
|
1-15 jun
|
8-10
|
104
|
9,6
|
7-10
|
33
|
8,6
|
|
16-30 jun
|
7-10
|
253
|
9,7
|
6-10
|
65
|
8,2
|
|
1-15 jul
|
6-10
|
605
|
9,2
|
5-10
|
176
|
7,4
|
|
16-31 jul
|
-
|
-
|
-
|
4-8
|
44
|
6,4
|
|
1-15 aug
|
3-10
|
143
|
6,6
|
3-10
|
165
|
5,2
|
|
16-31 aug
|
2-10
|
1284
|
5,4
|
3-8
|
127
|
4,6
|
|
1-15 sep
|
1-10
|
300
|
3,6
|
0-7
|
234
|
3,3
|
|
16-30 sep
|
0-7
|
645
|
2,9
|
0-7
|
173
|
2,1
|
|
1-15 oct
|
0-9
|
733
|
2,2
|
0-4
|
328
|
0,9
|
|
16-31 oct
|
0-10
|
750
|
1,3
|
0-3
|
244
|
0,3
|
|
1-15 nov
|
0-3
|
138
|
0,2
|
0-3
|
604
|
0,1
|
|
16-30 nov
|
0
|
5
|
0
|
0-1
|
341
|
0,0
|
LINEAR REGRESSION
Onset of primary moult can best be illustrated by a sinusoid for the first few weeks and last weeks, but there appears to be linear dependency over much of the central moult period.
LINEAR REGRESSION FOR OLD REMAINING PRIMARIES
Complete sample: Linear regression (n = 6171, R2= 0.820, sign: P<0,000)
PMS = -0,381* WEEK + 17,967
Ringed adults: Linear regression (n = 2069, R2= 0.800, sign: P<0,000)
PMS = -0,325* WEEK + 16,270
Unringed adult: Linear regression (n = 4102, R2= 0.779, sign: P<0,000)
PMS = -0,513* WEEK + 23,031
LINEAR REGRESSION FOR NEW FULLY GROWN PRIMARIES
Complete sample: Linear regression (n = 2969, R2= 0.930, sign: P<0,000)
PMS = 0,302* WEEK - 5,933
Ringed adults: Linear regression (n = 1209, R2= 0.888, sign: P<0,000)
PMS = 0,252* WEEK - 4,747
Unringed adult: Linear regression (n = 1760, R2= 0.833, sign: P<0,000)
PMS = 0,442* WEEK - 11,906
| Remaining old primaries in adult LBBGs, August 2001. |
| |
10 |
9 |
8 |
7 |
6 |
5 |
4 |
3 |
2 |
n: |
m: |
V: |
SD: |
SE: |
| 15/08: |
6 |
7 |
19 |
21 |
22 |
39 |
18 |
1 |
- |
133 |
6,20 |
2,81 |
1,68 |
0,15 |
| 21/08: |
13 |
10 |
22 |
32 |
43 |
102 |
49 |
2 |
- |
273 |
5,82 |
2,67 |
1,63 |
0,10 |
| 28/08: |
14 |
14 |
25 |
28 |
93 |
158 |
139 |
47 |
1 |
519 |
5,22 |
2,54 |
1,59 |
0,07 |
First cell (10, 15/08 = 6) should be read: on August 15 2001, 6 adults had all 10 primaries old, hence showed no primary moult yet (this is about 4% on 133 observed adults that day).
n: observations.
m: average.
V (= s2): variance.
SD (= s): standard deviation.
SE (s / sqr n): standard error. |
| Survey August 16 2001 Maasvlakte, the Netherlands. Adult primary score in the colony; adults with begging youngs. |
| p3 old |
p4 old |
p5 old |
p6 old |
p7 old |
p8 old |
n: |
average: |
| 1 |
3 |
3 |
2 |
1 |
1 |
11 |
5,82 |
| Survey of old primaries in adult LBBG on August 22 2002 at Maasvlakte, the Netherlands (51.57N,04.03E). |
| |
Dintelhaven |
Missouriweg |
Papegaaienbek |
| p1 old |
2 |
- |
1 |
| p2 old |
4 |
1 |
5 |
| p3 old |
8 |
- |
8 |
| p4 old |
32 |
1 |
10 |
| p5 old |
44 |
7 |
14 |
| p6 old |
96 |
26 |
12 |
| p7 old |
65 |
12 |
9 |
| p8 old |
3 |
- |
- |
| p9 old |
1 |
- |
- |
| p10 old |
- |
- |
- |
old prims n
old prim m
old prims SD
old prims SE |
255
5.7
1.28
0.08 |
47
6.0
0.92
0.13 |
59
4.7
1.59
0.21 |
|
Notes:
- For exact location, view the map of Maasvlakte.
- n = observations; m = average; SD = standard deviation; SE (s / sqr n) = standard error.
- In the Dintelhaven sample, another 7 birds were scored with "at least P5 old" in the folded wing, hence P5 or inner primaries still present. In the extreme case these birds had the complete primary set old, this would influence the average m by 0.1.
- old prim m must be read as "primary moult arrived at this stage for remaining old primaries in average adult LBBG".
- Regarding Dintelhaven: Adult primary score in the colony. Scored adults at a small pool which is used to bath and preen by adults from the Dintelhaven colony.
- Regarding Missouriweg: Adult birds feeding begging fledglings in the colony.
- Regarding Papegaaienbek: A mixed flock of adults preening at the sandy shores before returning to the Papegaaienbek colony together with Scandinavian adults using the beaches as stop-over resting point.
|
|
.
adult LBBG Belgium: graellsii "Dutch intergrade"
.
|
 LBBG 6cy AFAF, August 15 2003, Westkapelle, the Netherlands. |
 LBBG 7cy BNAH, August 01 2003, Zeebrugge, Belgium. |
 LBBG 7+cy BUAM, August 01 2003, Zeebrugge, Belgium. |
.
adult LBBG the Netherlands:
graellsii "Dutch intergrade"
.
|
 LBBG 9cy E246, August 24 2003, Texel, the Netherlands. P1 missing. |
 LBBG 7cy E914, August 18 2001, Missouriweg Maasvlakte, the Netherlands. P6 shed, P7-P10 are still old. |
 LBBG 9cy EM21, August 15 2004, Missouriweg Maasvlakte, the Netherlands. Ringed as pullus on July 10 1996. |
 LBBG 11cy KR7 August 12 2004, Westkapelle, the Netherlands. Dark individual. Ringed July 07 1993. |
 LBBG 9cy EV24 August 12 2004, Westkapelle, the Netherlands. dark individual. Ringed July 12 1996. |
 LBBG 11cy ME9 August 12 2004, Westkapelle, the Netherlands. dark individual. Ringed July 01 1993. |
 LBBG adult N527 August 04 2010, Heemskerk, the Netherlands. Ringed in Spain in winter. |
 LBBG hybrid =3, August 22 2003, IJmuiden, the Netherlands. Ringed in the Netherlands in 1999. |
 LBBG adult NLA 5.333.53x, August 28 2003, IJmuiden, the Netherlands. Ringed in the Netherlands. P8-P10 are still old, P5 slightly shorter than P4. |
.
adult LBBG Denmark: intermedius
.
|
 LBBG adult DKC 4271507 August 12 2004, Westkapelle, the Netherlands. Ringed in Denmark. |
.
adult LBBG Norway: intermedius
.
|
 LBBG adult NOS 4209478 August 12 2004, Westkapelle, the Netherlands. Ringed in Norway. |
 LBBG adult NOS 4111326, August 29 2003, IJmuiden, the Netherlands. Ringed in Norway. P5-P10 are still old, P3 fully grown. |
 LBBG adult NOS 4163669, August 29 2003, IJmuiden, the Netherlands. P7-P10 are still old, P3 fully grown. |
 LBBG adult NOS 4191125, August 28 2003, IJmuiden, the Netherlands. P6-P10 are still old, P3 fully grown. |
 LBBG adult NOS 492081, August 11 2003, Boulogne/Mer, France. P5-P10 are still old. All rectrices old. |
.
adult LBBG Sweden: intermedius
.
|
 LBBG adult SVS 8081001, August 28 2003, IJmuiden, the Netherlands. Ringed in Sweden. P5-P10 are still old, P2 is fully grown. |
.
adult LBBG unringed
.
|
 LBBG adult, August 16 2001, Vuurtorenvlakte Maasvlakte, the Netherlands. Still no primary moulted: p1-p10 old. |
 LBBG adult, August 18 2001, Missouriweg Maasvlakte, the Netherlands. Adult from the colony; p5 missing, p6 old. |
 LBBG adult, August 18 2001, Missouriweg Maasvlakte, the Netherlands. Adult from the colony; p5 missing, p6 old. |
 LBBG adult, August 18 2001, Missouriweg Maasvlakte, the Netherlands. P7-p10 old, p6 shed. |
 Photo 10: LBBG adult, August 24 2003, Texel, the Netherlands. P1-10 old. |
 Photo 11: LBBG adult, August 24 2003, Texel, the Netherlands. P1-10 old. |
|
|
Lesser Black-backed Gull- Kleine Mantelmeeuw (graellsii & intermedius)