DOI: 10.5061/dryad.cnp5hqc2b
title: How to learn to recognize conspecific brood parasitic offspring

description: Recognition systems evolve to reduce the risk and costs of making
 recognition errors. Two sources of recognition error include perceptual
 error (error arising from inability to discriminate between objects) and
 template error (error arising from using the wrong recognition template).
 We focus on how template error shapes host defense against avian brood
 parasites. Prior experiments in American coots (Fulica americana), a
 conspecific brood parasite, demonstrated how hosts learn to recognize
 brood parasitic chicks by using predictable patterns of hatching order of
 host and parasite eggs. Here, we use these results to quantify
 the benefit of chick rejection as well as the cost of template error, and
 we then use mathematical models to explore fitness payoffs of chick
 recognition from different template acquisition mechanisms. We
 find that fitness differences between mechanisms do not fully explain
 aspects of the learning mechanism, such as why coots reacquire
 their recognition template each year. Other constraints arising
 from mating systems and genetic mechanisms likely influence which learning
 mechanisms for parasitic chick recognition is optimal. Our approach could
 be expanded to explore how mechanisms of template acquisition
 influence other recognition systems, including parasitic chick recognition
 in other brood parasite hosts.
description: <i>Field data
 collection </i> We studied the
 dynamics of brood parasitism in American coots in wetlands near Williams
 Lake, British Columbia in 1987-1990 (417 nests) and again from 2005-2008
 (258 nests). We monitored nests every 1-4 days during egg laying, and new
 eggs were marked individually with indelible pen on each nest check. We
 detected brood parasitism when we found more than one egg laid in a nest
 per day and identified parasitic eggs using egg features like shape and
 color. The accuracy of these methods has been previously validated using
 genetic techniques (Lyon et al. 2002). We monitored nests daily during the
 3-9 day hatching period. For analyses of hatching patterns, we used 63
 nests for which both laying sequence and hatching sequence of parasites
 relative to hosts were known. Calculations of relative survival of hosts
 and parasites at control broods (i.e. naturally parasitized broods that
 were unmanipulated except for chick tagging) were based on 35 nests for
 which detailed censuses were conducted until the end of the parental care
 period. For both control
 and experimental nests, we hatched chicks in captivity to assure complete
 accuracy in matching each chick to the egg it hatched from. We took eggs
 from nests at first sign of pipping, typically one or two days before the
 chicks hatched. We then hatched each egg inside an individual mesh pouch
 in an incubator (Hovabator 1602N, GQF Manufacturing, Savannah, GA). We
 returned the chicks to nests within 24 hours of hatching, after attaching
 color-coded nape tags that were individually unique at each brood (Arnold
 et al. 2011). Because of a high degree of hatching asynchrony, nests were
 never left with less than two eggs or chicks, and parents did not abandon
 the nest during this period. We conducted
 censuses periodically for at least 20 days, and up to 35 days, after the
 last chick was returned to the nest. Brood censuses and behavioral
 observations were conducted at close range (10-40 m) from floating blinds
 equipped with camouflage coverings, where the individually distinct chick
 tags could be observed easily with binoculars. We determined survival by
 counting chicks that were seen in one of the last two censuses.
 <i>Cross-fostering
 experiment design</i> We conducted
 cross-fostering experiments to investigate the learning mechanism used in
 chick recognition (Shizuka & Lyon 2010). In the “Host First”
 experiment, the hosts were provided with their own offspring during the
 learning period, i.e., first day of hatching. Conversely, in the ‘Foreign
 First’ experiment, we provided the experimental hosts with foreign chicks
 (i.e., experimental parasitic chicks) on the first hatching day. In both
 treatments, on all days after the first hatching day we matched each host
 chick that hatched on a given day with a foreign chick of the same age.
 All foreign chicks used in a given experimental nest came from the same
 donor clutch so that all nests had chicks from only two sets of parents.
 Subsequent survival rates of chicks in experimental broods were assessed
 using the same protocol as control broods.
description: Survival Rate_Natural.xls<br> This is a worksheet that
 shows how we calculated the values presented in Table 1, which shows the
 expected and observed survival rates of hosts in natural (control) broods
 with parasitic chicks. The data are broken down into the two sampling
 periods: 1987-90 (collected by BEL) and 2005-08 (collected by DS and BEL).
 The formulas used to calculate summary data are preserved in the cells of
 the spreadsheet. This summary data is presented in lieu of the raw data
 since the data format for the two sampling periods were saved in different
 formats. For each hatch order category, the yellow
 highlighted cells show the number of nests used, observed number of host
 chicks that survived vs. died, and number of all chicks (host + parasite)
 survived vs. died. The green highlighted cells show the observed
 proportion of chicks survived for each hatch order category. These values
 are used in Table 1 to calculate the benefit of rejection in natural
 broods.  #####
 HF-FF_Survival.xlsx<br> This is the raw data that can be
 used to calculate survival rates used in Table 2. The raw data is provided
 from the single year (2008) when all "Host First" and
 "Foreign First" experiments were conducted. <br>