NIENHUIS J (2022) Do Northern Lapwings Vanellus vanellus adjust the start of egg laying to the activity of earthworms?. LIMOSA 95 (1): 28-40.
Most species adjust the timing of breeding to optimal
conditions. This is often a combination of the best conditions
for females to produce eggs and the best moment to start
laying eggs in order to have chicks when their food is
abundant. These conditions may differ between years. In
warmer springs Northern Lapwings breed earlier, and due
to climate warming they consequently advanced the start
of egg laying.
Before laying eggs, females have to accumulate sufficient
nutrients to produce eggs and energy reserves for incubation.
Like most waders, Northern Lapwings collect these energy
reserves on the breeding grounds. The predominant food
source of Northern Lapwings are earthworms. The more
earthworms are present, the fewer time it takes to produce
eggs. Earthworm presence is not the same as availability.
Lapwings use their vision to hunt and earthworms mainly
Detritivore earthworms like the common Lumbricus terrestris
surface to feed, mostly at night. At low temperatures during
winter this species is inactive. Early in spring they become
active and feed aboveground. After having collected
sufficient food they surface less frequently in summer. As a
consequence there is a period in spring when earthworms
are more available for eyesight hunters like plovers. Does
this affect the timing of the initiation of egg laying in
Data on the onset of egg laying of Northern Lapwings were
collected by volunteers protecting meadow bird nests from
farming activities. Only observations from the first peak in
egg laying were used as the second peak mainly consists of
replacement clutches after failed first breeding attempts.
Surfacing earthworms were counted at night in a firebreak
of a 30 year old residential area, where they live under
sidewalk tiles. Daily counts were conducted between 9
October 2015 and 28 October 2016 and during four springs
(2017-20). Numbers were related to environmental variables
using a regression analysis. Based on literature, the Northern
Lapwing breeding season was defined as 18 March-1
July. To determine the period with increased numbers of
surfacing earthworms, observed numbers were compared
to predicted earthworm numbers based on the outcome of
the abovementioned initial regression analysis, solely based
on the relationships for the non-breeding season.
Earthworm numbers were higher in conditions preventing
dehydration, such as for example moisty conditions.
During the Northern Lapwing breeding season more
foraging earthworms were counted than expected from the
predictions based on the non-breeding season.
The start of the period of elevated numbers of surfacing
earthworms was 2-31 days before the start of egg laying by
the Northern Lapwings. Both the onset of higher numbers
of surfacing earthworms and the onset of incubation were
affected by temperature, but this relationship was much
steeper for earthworms. Consequently, in an early (warm)
spring, there was a larger gap between the onset of surfacing
earthworms and the onset in egg laying. In very late (cold)
springs this difference almost disappears, probably as the
Northern Lapwings are time stressed to initiate breeding.
We conclude, that temperature driven variation in the
timing of the onset of (mass) surfacing of earthworms could
form an additive ultimate factor affecting the onset of egg
laying in Northern Lapwing.
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